Quantum Sensing, Imaging, and Precision Metrology III

Atom chip based interferometry holds signicant promise for embedded precise measurements of time, accelerations, rotations, and magnetic fields. It can enable compact sensors for various carriers like planes, boats, and drones, making it advantageous for navigation applications. When measuring acceleration with a cold atom interferometer, it is necessary to separate the two states during the interferometry sequence. Microwave dressed potentials generated from CPWs within a magnetic trap are one approach to achieve such on-chip manipulation. Two specic challenges arise in this process. First, the microwave field emitted by a waveguide introduces an AC Zeeman shifts, leading to a bias phase in the interferometer output. Precise determination of this bias is necessary for accurate parameter readout. Second, positioning the atom trap accurately between the two waveguides is crucial to obtain the necessary symmetry during separation; otherwise, the contrast of the interferometer is signicantly reduced. To address these challenges, we present a method for measuring AC Zeeman shifts using Ramsey interferometry.

Cold atom technology holds great promises to realize clocks, accelerometers or gyrometers with excellent stability and sensitivity. Atom chips are a compact choice for inertial navigation applications by using DC currents and microwave fields to trap and manipulate atoms close to the surface. Such a design decouples the size of the sensor from its sensitivity, enabling it to be used on different carriers like aircraft, submarine, or drone. We study the noise budget of an on-chip cold atom Ramsey interferometer with a state selective spatial splitting, which corresponds to an accelerometer configuration. We give a preliminary review of the different noise sources and their respective magnitudes.

An inertial navigation system (INS) demonstrator utilising atom interferometry is presented. Laser cooled rubidium-87 atoms in a grating magneto-optical trap (gMOT) are used to measure acceleration along a single axis. The system demonstrates a novel technique in quantum-enabled navigation which could offer significant improvement in precision and reduction in the drift present in classical INSs. Ruggedised lasers and control electronics allow potential deployment in maritime navigation in global navigation satellite system (GNSS) denied environments. Considerations are made towards a pathway for modular expansion and development of the system to 6-axis operation.

Light pulse atomic interferometry is a promising tool for fundamental scientific studies such as measurement of gravitational constant, fine structure constant and for inertial sensing. Introduction of simultaneous internal-state transitions on each branch of an atom interferometer has the capability of being sensitive to the test of weak equivalence principle as well as measurement of gravitational red shift due to the rejection of common mode noise sources. Strontium, with the 1S0→3P0 clock transition, is one possible candidate to implement atomic clock interferometry. In this talk, I will describe a dual atomic interferometry scheme where the same interferometric sequence is simultaneously performed on the ground and clock states of strontium atoms.

Point source atom interferometry (PSI) offers a low-complexity path for realizing multi-axis rotation measurements in a compact setup. This technique presents a strong immunity to acceleration direction and amplitude noise, making it a good candidate for developing fieldable devices. We present sensitivity improvements in our PSI gyroscope [1], leading to a fractional rotation rate uncertainty at the μrad/s level in a cubic centimeter volume and progress toward accuracy at the same level. We discuss systematic effects including spatially inhomogeneous light shifts, wavefront aberrations, and magnetic shifts which contribute to our accuracy error budget and present on our efforts to minimize these effects. We conclude with an outlook for future performance limits of PSI in compact systems. [1] Y.-J. Chen, A. Hansen, G. W. Hoth, E. Ivanov, B. Pelle, J. Kitching, and E. A. Donley, Single-Source Multi-axis Cold-Atom Interferometer in a Centimeter-Scale Cell, Phys. Rev. Applied 12, 014019 (2019).

Very Long Baseline Atom Interferometry (VLBAI) enables ground-based atomic matter-wave interferometry on large scales in space and time. With shot noise-limited instabilities better than 10−9 m/s2 at 1 s at the horizon, the Hannover VLBAI facility may compete with state-of-the-art superconducting gravimeters, while providing absolute instead of relative gravity measurements. Operated with rubidium and ytterbium simultaneously, tests of the universality of free fall at a level of parts in 10^13 and beyond are in reach. Finally, the large spatial extent of the interferometer allows one to probe the limits of coherence at macroscopic scales as well as the interplay of quantum mechanics and gravity. We report on the status of and first results obtained in the VLBAI facility which commenced operation in 2024.

Dark energy constitutes ~70% of the universe, which explains the observed accelerated expansion of the universe. It is conjectured that it is a new scalar field that interacts normal matter at the cosmological scale. Recently, cold atom experiments in laboratory have contributed significantly on the constraints of scalar-field models such as chameleon and symmetron. These experiments are currently limited by the knowledge of the Newtonian gravity of the test masses. In this talk, we will present a joint project of D3E3/DESIRE between JPL and Leibniz University Hannover, in which atom interferometers will be implemented in the four-second microgravity environment in the drop tower of the Einstein-Elevator facility at the Hannover Institute of Technology, Germany. We will illustrate the measurement concept for constraining dark energy models, and report the progress of the joint effort. This research was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the NASA. The DESIRE project is supported by the German Space Agency DLR with funds provided by the Federal Ministry of Economic Affairs and Climate Action (BMWK).

Atom interferometers make use of the interference of matter waves for precise measurement of motion. Employing 3D-laser-cooled atoms provides improved fringe contrast, while measuring in a continuous beam architectures provides high-bandwidth measurement, error suppression of time-varying signals, and the elimination of measurement dead time. In this presentation, we will discuss the initial observation of interference signals in a dual-beam, 3D-cooled atomic beam interferometer architecture. Additionally, we will demonstrate improvements in the measurement bandwidth of the interferometer through novel readout and phase estimation methods.

Atom interferometry promises a major leap in improving the precision and accuracy of matter-wave sensors. With their ever-increasing sensitivity, atom interferometers are expected to become an integral part of a new generation of quantum sensors, enabling high-precision measurements of inertial and electromagnetic forces, accurate determination of fundamental constants, tests of fundamental laws of modern physics, or detection of gravitational waves. At levels of precision beyond the state of the art, high fidelity modelling of the sensor becomes crucial. On the one hand, novel analytical approaches to matter-wave interferometers need to be developed and on the other, efficient numerical time-dependent solvers capable of dealing with real-life perturbations, noise and aberrations are also necessary. This contribution gives an overview of the tools of both categories illustrated with concrete examples from recent experiments where quantum gas sensors are pushed beyond the state of the art.

Nitrogen vacancy centers (NV) in diamond are promising quantum systems for magnetic field sensing. The sensitivity of such a quantum sensor can be greatly increased by using stimulated emission of the NV centers in laser threshold magnetometry (LTM), which is projected to reach the fT/sqrt(Hz) regime. Previous implementations relied on external seed lasers, pulsed operation, or sensing via NV-absorption. In our work, we combine the NV centers with a second gain medium within the same cavity, achieving self-sustainable cw lasing. The laser system shows a magnetic field-dependent laser threshold, which is the basis of high-sensitivity NV magnetometry via LTM.

Nitrogen vacancy (NV) centers in diamond are robust quantum sensors with long spin coherence times that can be used for high-sensitivity local magnetometry with nanoscale resolution. Recently, covariance magnetometry has been developed in which two or more NV centers are simultaneously measured to detect the presence of correlations in fluctuating magnetic fields across space or time. So far, covariance magnetometry has been limited to the detection of NV centers that are spatially resolved, with separations beyond the optical diffraction limit. I will describe methods to detect the presence of correlated noise using two NV centers that are unresolved, enabling covariance magnetometry at nanometer length scales. These methods include a new phase cycling protocol for low magnetic fields, the use of local 13C nuclei as spin handles for phase cycling at high magnetic fields, and entangled Bell-pair states as a sensing resource for closely-spaced NV centers.

As the ability to control electromagnetic fields through engineered photonic structures grows, so does our need for field mapping techniques with subwavelength resolution. Here, we use a scanning diamond nanocrystal to investigate the interplay between the emission of room-temperature nitrogen-vacancy (NV) centers and a proximal topological waveguide. The NV photoluminescence serves as a local, spectrally broad light source to characterize the waveguide response, both in terms of its wavelength bandwidth as well as the correspondence between light injection site and directionality of wave propagation. Further, we find that near-field coupling between the emitters and the waveguide chiral modes influences the ellipticity of the NV photoluminescence, hence allowing us to reveal nanostructured light fields with a spatial resolution defined by the nanoparticle size. Our results pave the route to exploiting color centers as photonic sensors, an approach that also promises opportunities in the development of on-chip devices integrating single-photon emitters and quantum optics.

The nitrogen-vacancy (NV) centre in diamond has emerged in the past two decades as a unique multi-modal sensor, combining the good sensitivity, stability and accuracy of quantum sensors in a solid diamond, small and easy-to-integrate while allowing for high spatial resolution. NV centres in diamond are especially good magnetometers, providing an intrinsic vectorial measurement of the magnetic field. Founded in 2020, Kwan-tek is a start-up company aiming to develop NV-based sensors for industrial applications. By leveraging the stability of NV sensors, Kwan-tek is currently developing a metrology product for stabilizing magnetic fields in the 1-30 mT range, with 1 nT per day stability. NV centers have also drawn attention for navigation applications where their intrinsic vectorial capability, coupled to long term stability are good benefits for magnetic compassing. In accordance, Kwan-tek has recently started the conception and development of a three axes magnetometer, aiming to provide the aforementioned properties, coupled with a good SWaP-C in order to address broad embedded applications.

Quantum sensors provide sensitivity that is unattainable by classical sensors, allowing detection of the weak magnetic fields associated with the presence of rare earth elements (REEs). A specific electronic spin state in nitrogen vacancies in nanodiamonds has energies and a spin lifetime that are highly dependent on local electromagnetic fields, temperature, and pressure, and thus can be used to engineer very sensitive sensors for the detection of these physical quantities. We perform optically detected magnetic resonance (ODMR) and spin relaxometry measurements to quantify the ODMR spectra and spin relaxation time as a function of REE concentration.

The nitrogen-vacancy (NV) center in a nanodiamond (ND) crystal is a promising material for quantum information processing, sensing, and computing applications. Owing to the tunability of the qubits defined within the NV centers, NV centers are potential candidates for the sensing chemical analytes, electric and magnetic field, pressure and temperature sensing applications. Using the effective Hamiltonian, energy shift and split per unit stress application it is possible to calculate and quantify the stress sensitivity using spin coherence time at the triplet ground state. By combining the DFT and Hamiltonian modelling results, we discuss the superiority of the quantum sensing for pressure and field monitoring over traditional optical sensing based on the band gap and band edges tuning.

In this presentation, we will introduce our proposed compact chip-scale nano-NMR (Nuclear Magnetic Resonance) sensors designed to measure the D/H ratio in water. This ratio is critical for tracing the origins of water, allowing us to distinguish between sources such as comets, asteroids, solar wind implantation, or outgassing from a moon's interior. This research aims to uncover new insights into the early history of the moons and inner planets. Our sensor's core technology relies on color defects in diamonds, specifically NV (Nitrogen-Vacancy) centers. These sensors are inherently robust, lightweight, and have a small footprint, making them ideal for in-situ measurements during space missions. This work is supported by NASA under contract 80NSSC24CA146.

Collective atom-photon interaction has been actively explored in recent years. Control and manipulation on the collective states of atomic system could bring new opportunities for quantum many-body physics and quantum networks. In this talk, we discuss about our investigation on the signatures of collective emission from a dense atomic ensemble coupled to a nanophotonic resonator. With our recent experimental realization of trapping a dense atomic ensemble on an integrated nanophotonic microring resonator, we can study how the ensemble collectively couples to a photonic channel in the resonator and other free pace modes. Specifically, we will show the decay dynamics of an atomic ensemble following long and short excitation pulses, with the former driving the system into a steady-state and the latter into a so-called timed-Dicke state. Our study could shed light on the realization of selective radiance and enable new explorations of collective quantum optics with trapped atoms coupled to nanophotonic circuits.

High-finesse optical microcavities are at the core of a wide range of scientific advances and technical applications from quantum technologies to optical sensors. Among them, fiber Fabry-Perot cavities (FFPCs) are of particular interest because of their unique properties. However, integrating FFPCs into photonic devices remains difficult because it is complex to individually tune their resonance frequencies. Moreover, integrating them in a miniaturized device is an experimental challenge prone to errors. To tackle this problem, we combined FFPCs with femtosecond laser manufacturing to create the very first integrated FFPC on a glass substrate. Post-assembly fine tuning is performed to maximize the finesse by actuating an integrated flexible mechanism. These integrated FFPCs devices pave the way to new scalable and miniaturized photonic sensors with extremely high resolution particularly interesting for quantum applications.

Gravity holds great potential as a sensing channel: all matter gravitates, and this effect cannot be shielded. Gravity is so weak however, that extraordinary sensitivity is required to actualize this potential. In this talk, I will discuss a novel atomic gravimeter configuration that (a) has sufficient sensitivity to be a useful gravitational sensor, (b) is small, light and robust enough to operate as a mobile payload, and (c) has excellent spatial resolution for laboratory-scale fundamental physics research.

We present a novel atom interferometer geometry in which the differential signal of two co-located interferometers singles out a phase shift proportional to the curvature of the gravitational potential. The scale factor depends only on well controlled quantities, namely the photon wave number, the interferometer time and the atomic recoil, which allows the curvature to be accurately inferred from a measured phase. As a case study, we numerically simulate such a co-located gradiometric interferometer in the context of the Hannover very long baseline atom interferometer facility and prove the robustness of the phase shift in gravitational fields with complex spatial dependence. We define an estimator of the gravitational curvature for non-trivial gravitational fields and calculate the trade-off between signal strength and estimation accuracy with regard to spatial resolution.

We experimentally demonstrate precise Raman matterwave control at an intermediate single-photon detuning where a balance between the optical power efficiency with the requirements on the control speed and the suppression of excited-state dynamics can be adjusted. The method is based on composite biased rotation that exploits the proportionality between the traditionally “unwanted” light shift with the Raman coupling. The nanosecond control is fast enough to be immune to low-frequency noises, so our system can be accurately modeled. The ℱ> 99.2% fidelity is estimated with standard single-qubit quantum process tomography and randomized benchmarking methods. Our work suggests highly precise spinor matterwave controls are achievable for large atomic samples with moderate laser power, even in noisy environment.

In cold-atom quantum optical interfaces, optical control is commonly achieved by weakly dressing atoms within their ground or metastable states. However, precise control over strong atomic transitions can dramatically enhance single-atom manipulation and enable efficient control of collective emission dynamics, opening a pathway to novel regimes in atomic and quantum optics. We use shaped sub-nanosecond pulses to achieve precise optical control of strong transitions. By driving an auxiliary transition, we induce a strong optical force that accelerates atoms in their ground state while leaving the excited-state component intact. This creates a strong phase mismatch, coherently halting optical propagation within the atomic ensemble. Upon restarting superradiance, the interaction effects accumulated 'in the dark' are transmitted to the far field. We observe a density-dependent decay of spin-wave coherence due to near-field pairwise interactions, which is analogous to dipolar relaxation in the microwave domain. Finally, we discuss ongoing efforts to implement this technique in a nanofiber interface for subradiance-assisted optical storage

Trapped ions are a promising approach to low-SWaP, high-performance atomic clocks. Here, we discuss different approaches of trapped ion atomic clocks under development at JPL aimed at reducing the size and power while maintaining performances. We will focus on the micro-mercury trapped ion microwave clock and a single trapped ytterbium ion optical clock. We will also mention some of the efforts in investigating the feasibility of realizing integrated-photonic chip optical clock with multiple trapped ions.

We are studying a new spectroscopic method using laser-cooled rubidium atoms that allows us to lock the carrier frequency of modulated laser in the coherent population trapping (CPT) clock experiment. This method uses counter-propagation of the bichromatic laser field produced by the modulated laser. The counter-propagation cancels the CPT effect near the optical resonance and gives rise to enhanced Doppler-free absorptive resonances with high-contrast away from the transition. We demonstrate the CPT clock operation by locking the modulated laser using this resonance. We also describe a theoretical model that we have developed based on density-matrix formalism to simulate this spectroscopic scheme for accurately predicting the lineshape and amplitude of resonances under different excitation conditions. Our study suggests that this spectroscopic method is also quite suiatble for developing cold-atom based optical frequency standard.

We report on our progress in developing chip-scale atomic beam clocks for timing holdover applications. Our approach is based on a chip-scale, Rb atomic beam platform using etched collimator structures [1] integrated into a compact, passively pumped device [2]. The clock signal is realized using Ramsey coherent population trapping (CPT) spectroscopy over a 1 cm distance with fractional frequency instability below 1 × 10-9 at 1 s of integration. We present a detailed characterization of systematics in this system arising from the finite Doppler width inherent in a compact beam geometry, the associated impact on resonant and off-resonant light shifts, and other key systematics which we control at the 10-12 level for integration times exceeding 104 s. Miniaturization efforts for the full clock system will be presented as well as an outlook for week-scale stability which could be achieved in this system [1] Li et al., "Cascaded collimator for atomic beams traveling in planar silicon devices," Nat Commun 10, 1831 (2019). [2] Martinez et al. “A chip-scale atomic beam clock,” Nat Commun 14, 3501 (2023).

The convergence of atomic spectroscopy, MEMS cell technologies and integrated photonics has led to the development and deployment of high-precision chip-scale atomic devices. In this talk, I will present studies performed at FEMTO-ST Institute, France, about the development of microcell-based microwave and optical atomic clocks. In the first part, I will talk about the demonstration of CPT-based microwave cell clocks with stability at 1 day in the low 10-12 range, made possible thanks to the combination of advanced Ramsey-based interrogation sequences and cells built with low gas permeation windows. In the second part, I will discuss the in-progress development of a microcell-based optical frequency reference based on the two-photon transition of Rb atom at 778 nm. An encouraging short-term stability of 3x10-13 at 1 s and 3x10-14 at 100 s has been recently achieved. Stability limitations are well-identified and paths for improvement will be discussed. I will also present some preliminary studies of lasers frequency-stabilized onto the Cs atom 6S1/2 - 7P1/2 transition at 459 nm in a microfabricated cell, in a simple-architecture setup.

We present compact laser distribution modules for the realization of low-SWaP (size, weight, and power) strontium-based optical clocks. These modules are designed for wavelengths between 461 nm to 707 nm and incorporate functionalities to stabilize laser intensity and fiber path lengths, as well as to enable modulation spectroscopy. This is achieved by integrating miniaturized free-space acousto- and electro-optic modulators into the modules. One such module also features two distributed Bragg reflector (DBR) laser chips emitting at 679 nm and 707 nm. We present the module designs and show results of the characterization of the first assembled module.

In 1976 Kroger and Reich established the existence of a low-lying nuclear excited state in 229Th through the spectroscopy of γ rays emitted following the α decay of 233U. The prospects of a laser-accessible nuclear transition touched off a flurry of proposals to utilize this apparently unique nuclear transition as a sensitive probe of both nuclear structure and chemical environment, to constrain physics beyond the Standard Model, and to construct a clock with unprecedented performance. Unfortunately, Kroger and Reich could only tell us that the transition energy was less than about 100 eV and therefore scientists have spent the intervening 48 years searching for the thorium nuclear transition. I’ll describe our efforts over the last 16 years to construct the first thorium-doped crystals and their use to perform nuclear laser spectroscopy, resulting in a measurement of the nuclear transition energy as 8.355733(2)stat(10)sys eV in 229Th:LiSrAlF6. I will also discuss recent work observing the nuclear transition in thin films of 229ThF4; ongoing work to understand and harness the effect of the crystalline host on the isomeric transition; and the next steps for using this transition to probe new physics and build better clocks. This work was funded by the NSF and ARO.

The development of optical quantum technologies often involves high-resolution spectroscopy at wavelengths in the visible and short near-infrared regimes, depending on the specific physical platforms being studied (e.g., neutral atoms, trapped ions, solid-state color centers, etc). Here, we show a versatile approach to this problem through the spectral translation of electro-optic frequency combs using nonlinear integrated photonics. This approach enables a single pump laser and modulator technology to perform spectroscopy across a broad range of wavelengths. In the current implementation, an electro-optic comb centered at 780 nm and containing as many as one million comb teeth with a 1 kHz spacing is spectrally translated to wavelengths between 589 nm and 1150 nm using a chip-based nonlinear microresonator, and sub-Doppler spectroscopy of hyperfine transitions in Cs vapor is demonstrated.

We use semi-supervised and unsupervised machine learning to optimize the placement of optical frequency combs for identifying gas molecules in the atmosphere. These combs excite molecules, altering the light in characteristic ways, which helps identify the molecules present. We present several inexpensive, efficient machine learning methods to determine optimal placement of comb(s) to maximize our ability to distinguish which molecule is present in a sample from the resulting post-sample comb(s). Using synthetic datasets with several sources of realistic noise, our methods achieve high clustering accuracy with very small comb numbers and sizes. Our techniques can extend the practical usage of frequency combs to detect pollutants such as ammonia, methane, and organic hydroperoxides, aiding in pollution mitigation and climate change efforts.

In addition to standard projective measurements, quantum mechanics offers alternative methods for extracting information from a quantum system. Some of these methods lead to quasi-probability distributions for measured observables, which are not always positively defined. Analogous to the Wigner quasi-probability distribution, the presence of negative regions in these distributions can reveal purely quantum behaviors in the system or its dynamics. In this work, I will present a specific scheme, known as quantum non-demolition, in which quasi-probability distributions naturally arise. This scheme employs an additional quantum detector coupled to the system, enabling the extraction of crucial information about the system's wave function. Furthermore, I will show that this method provides a necessary and sufficient condition for identifying quantum features, offering a stronger criterion than the commonly used Leggett-Garg inequalities. I will explore the connection between this scheme and the violation of the Leggett-Garg inequalities, demonstrating how this approach unveils purely quantum effects and the quantum-to-classical transition caused by interactions with the environment.

Achieving transient-transmission measurements on a single epitaxial quantum dot, we observe the picosecond-scale dynamics of the exciton state. Through temporal beating of the absorption signal, the quantum coherence of an exciton is directly observed in the time domain. We find that the excess energy produced by a single-photon absorption is crucial to the generation of a coherent excitation.

Vector magnetic field measurement is required in several applications including magnetic surveys, navigation and anomalies detection. We have designed and developed a vector magnetometer prototype that can be deployed in the field to survey earth’s magnetic field. Vector operation is enabled in this prototype by using the phenomenon of synchronous coherent population trapping (SCPT), and combining it with a feedback compensation mechanism. The prototype utilizes a small rubidium cell which is placed inside a three-axis field coil. Magnetic field along each axis is measured by performing a peak-lock on one of the strongest resonances produced by SCPT and compensating the external magnetic field via servo control of the three-axis field coil. Under this locked condition, the feedback current applied to each coil in the three-axis system gives a real-time, single-shot measurement of the magnetic field components. Extensive testing of the prototype is being done by performing magnetic field measurements in the magnetically noisy environment inside the laboratory and in-comparison with that of a fluxgate sensor.

Hiromu Nakashima is a master course student at Department of Chemistry at Okayama University. He is developing a microwave excitation device particularly useful for quantum nanodiamond thermometry exploiting diamond nitrogen vacancy centers. The present work is now prepared for submission and has been recently awarded the Best Poster Award at the New Diamond & Nano Carbons 2024 international conference held in Sydney in 2024 May.

Here, we will introduce our recent work on integrating hollow whispering gallery resonators with nanoparticles, with an emphasis on NV centred diamond. The focus of the work is for quantum sensing and QKD studies; however, the talk will introduce some of the characterisation techniques we have developed to engineer the resonators to optimise the experimental configurations.

This work explores the design, fabrication and characterisation of gallium nitride (GaN) lasers for use in optical atomic clocks. Software allows the laser material and grating structures to be modelled and devices have been fabricated in the cleanroom based on this. Development of the etching process and metal contacts are being optimised to ensure the best quality lasers are produced. These devices can then be used for the cooling of atoms in optical atomic clocks taking what is currently a lab scale technology to something which is much more compact. Single mode GaN lasers with high output power and narrow linewidth have been realised for this purpose.

VECSELs have rapidly gained a position as an attractive laser solution for optical atomic clocks and quantum computers utilizing trapped ions and cold atoms. We report development of commercial VECSEL-systems and present recent developments for optical clocks including wavelength coverage for several clock transitions (eg. Yb 578nm, Sr 698 nm, Ca+ 729nm, Yb+ 436nm and 467nm, and Ba+ 1762 nm), long-term stability, noise suppression, and linewidth narrowing (sub-Hz with intracavity EOM).

Quantum structured light offers a roadmap to high-dimensional and multi-dimensional quantum states by exploiting all of light’s many degrees of freedom at the quantum level. In this talk, I will review the recent progress in quantum entanglement of photons in their spatial degree of freedom: quantum structured light. I will explain how to create high-dimensional quantum states in the laboratory, how to measure them, and review the present state of the art in the field. I will show how the patterns can be abstracted, mixing degrees of freedom to produce quantum topologies in light, introducing new paradigms for quantum state observables and classification. Finally, I will outline the advantages and disadvantages of using such single photon and entangled states in real-world applications, offering a perspective on the present challenges and exciting opportunities in the field.

Atomic clocks first developed in the 1950’s have become a mainstay of modern synchronization, navigation and communication. With an unprecedented accuracy, now surpassing 1 part in 10^18, optical atomic clocks would lose only 1 s per 15 billion years, could measure a meter stick with a length resolution at quark level, and are currently being used as tabletop experiments to search for physics beyond the standard model. This talk will take a forward-facing perspective on the evolution of atomic clocks, their enabling technologies, and developing applications. More specifically, I will explore the optical technology at the heart of atomic clocks and how these enabling technologies will help serve to advance the field of precision metrology.

When the largest telescopes can’t see all the way back to the Big Bang, and when the highest-energy accelerators cannot produce more massive particles, what is one to do? Laboratory-based precision measurements offer glimpses into the distant past and into the ultra-high-energy present. I will discuss how some of the most precise laboratory measurements are performed, with particular focus on measurements of the dipole moments of two relatively light particles, electrons and muons. I will ty to put the results in the context of the broader search for physics beyond the Standard Model.

The isolation of levitated optomechanical systems from their environment makes then attractive for measurement of weak forces, but also makes them challenging to precisely measure relative to the outside world. We will discuss optical techniques for precision measurement of the displacement of a particle levitated in a magneto-gravitational trap, for calibrating the magnification of realistic optomechanical systems, and for accurately locating a levitated particle relative to objects outside of the vacuum chamber containing the system.

We shall describe how opto-electro-mechanical devices can be designed and optimized for transducing optical and rf signals, either in reciprocal and nonreciprocal way. Under proper impedance matching conditions, detection of parameters changes of a system (e.g, pollutant or virus detection) can be enhanced compared to standard detectors. The role of nonreciprocity and controllable topological phases in the detection will be investigated.

We utilize a method using frequency combs to construct waves that feature superoscillations - local regions of the wave that exhibit a change in phase that the bandlimits of the wave should not otherwise allow. This method has been shown to create superoscillating regions that mimic any analytic function - even ones well outside the bandlimits - to an arbitrary degree of accuracy. We experimentally demonstrate that these waves are extremely robust against noise, allowing for accurate reconstruction of a superoscillating target function thoroughly buried in noise. We additionally show that such a construction can be easily used to range-resolve a signal well below the commonly accepted fundamental limit.

The resolution of optical systems, formulated as the smallest possible distance between two point sources for which they still can be dissolved, was for a long time believed to be limited by diffraction, formulated by the Rayleigh criterion. Recent advancements in quantum metrology have shown, by evaluation of the Quantum Cramér Rao bound (QCRB), that the Rayleigh criterion is not a fundamental limit. In our experiment, spatial-mode demultiplexing (SPADE) is used to estimate the separation of the sources below the Rayleigh limit. The experiment is extended to incorporate the measurement of additional parameters, such as power imbalance and centroid position of the two sources, bringing it closer to real-world applicability.

We previously demonstrated Quantum Microscopy by Coincidence (QMC) experimentally, showcasing balanced optics between the signal and idler arms to achieve super-resolution imaging with Heisenberg scaling. QMC utilizes quantum-entangled photon pairs traveling through symmetric paths, effectively acting as photons with half the wavelength, which double the spatial resolution. Here, we update our theoretical framework for this quantum imaging method, which surpasses the classical diffraction limit using the same optics. In QMC, only the signal photon interacts with the object, while the signal and idler photons do not intersect after departing from the source. Nevertheless, quantum correlation through coincidence counting provides the resolution doubling. We theoretically derive the quantum second-order correlation function, which leads to the determination of both the point-spread function and the convolution for an extended object. Although both detectors are sensitive solely to intensity, the phases of both arms still contribute to achieving super-resolution. We then compare these results with their classical counterparts to demonstrate the quantum advantage.

GaN laser diodes have the potential to be a key enabler for many quantum technologies, including quantum sensing, precision metrology, quantum communications and quantum computing, since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from ultra-violet to visible. Furthermore, GaN allows the development of very high specification laser diode sources that are portable, robust and provide practical solutions that are otherwise unobtainable using more conventional laser sources. Novel applications for quantum technologies include GaN laser sources for cold-atom interferometry, such as next generation optical atomic clocks, quantum sensors and quantum metrology. Several approaches are taken to achieve the required linewidth, wavelength and power for cold-atom interferometry, including an extended cavity GaN laser diode (ECLD) system, and a distributed feedback (DFB) GaN laser diode with side-wall etched nano-gratings. We report the development of a generic passive waveguide photonic integrated circuit (PICs) platform for quantum applications that covers all the key cold-atom wavelengths for quantum sensing,

As a complement to an existing Metrology graduate class, we have prepared three main practicals on single-photon detection, for illustrating the concepts of i) PDP, Poisson statistics and photoresponse non-uniformity, ii) DCR and afterpulsing, and iii) timing jitter. The students are provided with the basic installation using an off-the-shelf array of CMOS SPADs (SPAD23). In turn, they are asked to complete some missing code sections, plot and explain the resulting data. All functions are integrated in the sensor board and only a 5 V external power supply and a USB3 connection are needed, plus a pulsed light source for the TCSPC experiments (LED or laser).

Quantum structured light offers a roadmap to high-dimensional and multi-dimensional quantum states by exploiting all of light’s many degrees of freedom at the quantum level. In this talk, I will review the recent progress in quantum entanglement of photons in their spatial degree of freedom: quantum structured light. I will explain how to create high-dimensional quantum states in the laboratory, how to measure them, and review the present state of the art in the field. I will show how the patterns can be abstracted, mixing degrees of freedom to produce quantum topologies in light, introducing new paradigms for quantum state observables and classification. Finally, I will outline the advantages and disadvantages of using such single photon and entangled states in real-world applications, offering a perspective on the present challenges and exciting opportunities in the field.

Atomic clocks first developed in the 1950’s have become a mainstay of modern synchronization, navigation and communication. With an unprecedented accuracy, now surpassing 1 part in 10^18, optical atomic clocks would lose only 1 s per 15 billion years, could measure a meter stick with a length resolution at quark level, and are currently being used as tabletop experiments to search for physics beyond the standard model. This talk will take a forward-facing perspective on the evolution of atomic clocks, their enabling technologies, and developing applications. More specifically, I will explore the optical technology at the heart of atomic clocks and how these enabling technologies will help serve to advance the field of precision metrology.

When the largest telescopes can’t see all the way back to the Big Bang, and when the highest-energy accelerators cannot produce more massive particles, what is one to do? Laboratory-based precision measurements offer glimpses into the distant past and into the ultra-high-energy present. I will discuss how some of the most precise laboratory measurements are performed, with particular focus on measurements of the dipole moments of two relatively light particles, electrons and muons. I will ty to put the results in the context of the broader search for physics beyond the Standard Model.

Widely tunable optical parametric oscillator (OPO) lasers have recently shown great potential in quantum applications. Their ability to generate low noise, Watt-level optical power and access arbitrary wavelengths in the near-IR and mid-IR makes them ideal for nonlinear frequency conversion of non-telecom photons from atomic or solid-state systems into telecom photons, enabling photonic interconnects in quantum computing, sensing, and communication. Additionally, OPOs have been used for inducing high-Rabi-frequency optical excitations, such as in Rydberg sensing, by providing low-noise, high-power coherent light at hard-to-reach wavelengths. This presentation highlights the design of two OPO systems by TOPTICA Photonics, focusing on their quantum applications, including photon frequency conversion and atomic transitions at exotic wavelengths in the near-IR and mid-IR.

III-V semiconductors, composed of elements from groups III and V play a significant role in quantum information technology. Their unique properties make them highly suitable for applications in quantum computing, communication, and sensing. III-V semiconductors provide significant advantages for quantum information processing due to their superior High Electron Mobility and Bandgap Engineering and Tunability, III-V semiconductors are excellent materials with optical and spintronic properties for quantum dot qubits. This talk will breakdown why III-V semiconductors are so powerful for future of Quantum technology and will revolutionize Quantum Information .

Transduction of weak signals between the microwave and the optical frequency ranges stands to unlock powerful hybrid quantum information systems and sensors. While transducers have been realized on a variety of platforms, electro-optic transducers stand out due to their large bandwidths in the MHz to GHz range. Most microwave-to-optical quantum transducers suffer from thermal noise due to the absorption of strong pumps. In electro-optic transducers, pump-induced heating has caused a long-standing tradeoff between thermal noise and efficiency. We analyze the coupled thermal and wave dynamics in a two-step scheme based on an intermediate frequency state in the sub-THz range. Our analysis, supported by numerical simulations, shows that the two-step scheme operating with a continuous pump offers near-unity external efficiency with a multi-order noise suppression compared to the direct, “single-step” transduction. As a result, two-step electro-optic transducers may enable quantum noise-limited interfacing of superconducting quantum processors with optical channels at MHz-scale bitrates, and sensing across insufficiently accessible frequency ranges.

Programmable arrays of alkaline-earth atoms have emerged as a versatile experimental platform for quantum science. Together with Rydberg interactions, control at the single-particle level makes such atom arrays ideal systems for studying how quantum entanglement can be harnessed to improve the performance of optical atomic clocks. In this talk, I will discuss recent work from JILA, where we have achieved this goal by engineering Rydberg interactions to prepare entangled states with metrological gain.

Optical frequency combs, specialized mode-locked that serve as optical rulers for light, play an essential role across various quantum applications. At TOPTICA Photonics Inc., a leading authority in laser technology for quantum applications, we integrate various laser sources into difference frequency combs (DFCs), enabling applications that span from high-end systems such as optical atomic clocks to quantum networking and computing. In this presentation, I will dive into our innovative work and demonstrate how DFC system integration has opened new possibilities in metrology and sensing with a focus on high-precision distance measurement.

We present experiments aimed at the creation and study of non-Gaussian states of a mesoscopic mechanical oscillator. On the mechanical front, we have developped, fabricated and operated phononic-crystal SiN membranes, with mechanical quality factors in the 10^8 to 10^9 range. To allow resonant coupling of the membrane (typically in the MHz band) to a two-level system, we have developped a heavy fluxonium superconducting qubit architecture, with a transition frequeny as low as 1.8 MHz.. Design, fabrication and operation of the qubit in a 10 mK environment are discussed, together with a charge sensing experiment The long-term goal of these experiments is to create and explore non-Gaussian states of an electromechanical membrane.

Nonlinearities are a key resource throughout many facets of quantum science and they are central to quantum technology development and tests of the foundations of physics. In cavity quantum optomechanics, the radiation-pressure interaction is inherently nonlinear, coupling the optical intensity to the mechanical position and, less widely discussed, the response of the optical cavity itself is nonlinear. As a growing number of experiments are now confronting this nonlinear regime, a theoretical framework for describing these cavity optomechanical nonlinearities is needed. In this talk, a framework of cavity quantum optomechanics, which captures the nonlinearities of both the radiation-pressure interaction and the cavity-response will be introduced [1]. As applications of this framework, we show how to perform position measurement well beyond the applicability of the linearized regime [1], and, looking ahead, with only these nonlinearities, we show how mechanical Wigner negativity can be prepared deterministically in the unresolved sideband regime [2]. [1] J. Clarke, P. Neveu, K. E. Khosla, E. Verhagen, and M. R. Vanner, Phys. Rev. Lett. 131, 053601 (2023). [2] In preparation

LIDA is an ultimately squeezed-light-enhanced laser-interferometric detector for axions from the galactic halo, where the axion field induces a rotation of the polarization axis of a strong linearly polarized laser beam in a high-finesse cavity. The first observing run already established LIDA as one of the most sensitive direct axion detectors around axion masses of 2 neV, reaching a competitive sensitivity to the axion-photon coupling of 1.51*10^(-10) GeV^(-1). We provide an update of our second observing run that aims for a broadband probing of axion masses below neV and is designed to advance quantum-enhanced optical metrology by setting new direct detection constraints on the axion-photon coupling.

Optomechanical accelerometers have been proposed as detectors for vector ultralight dark matter. In this talk we present a cryogenic dark matter search using a resonant detector based on cm-scale nanomechanical membranes. Operating in a closed-cycle cryostat, we implement a custom vibration isolation system to suppress acoustic vibrations and enable thermalization to 4 K, and use photothermal frequency tuning to improve resonant detection bandwidth. We perform an analysis of the detector’s measured acceleration spectrum to search for dark matter signals around 40 kHz, corresponding to particle mass near 0.1 neV/c^2.

Non-gravitational detection of dark matter (DM) poses one of the most urgent questions in fundamental physics. Ultralight bosonic DM (UBDM) is a promising candidate whose coupling to the standard model (SM) of particle physics is expected to cause variations in the fundamental constants like the fine-structure constant and electron mass and consequently the Bohr radius. The latter causes an oscillation in the size of atoms and atomic bonds and hence the size of macroscopic crystalline materials at the UBDM’s Compton frequency. We employ one of the most precise position sensors–laser interferometry–to detect a differential length change of two optical cavities to set new bounds on the coupling constant of UBDM to the SM. In this talk, I will discuss our latest results from this two-cavity apparatus.

A new window to the universe has opened with the detection of Gravitational Waves (GW) by the Laser Interferometer GW Observatory (LIGO). GW interact weakly with matter carrying information about their origins across the universe without modification. LIGO senses GW frequencies only between 5 and 1000Hz, restricting it to observe a small sampling of events. We show the feasibility of a ground-based GW detector to fill the critical frequency gap from 10−3 Hz to 1 Hz, rich in important GW sources (intermediate mass ratio inspirals; high-mass galactic black hole binaries) which no current facility can see. The planned tabletop GW sensor is enabled by breakthroughs in frequency combs. While the LIGO measures the amplitude of interfering beams, we measure directly the signal phase, having demonstrated 10-10 radian sensitivity in a mode-locked cavity in which two pulses circulate. Sensitivity enhancement to be applied include miniaturization (100x), dispersion and squeezing.

At the Chapel Hill conference in 1957, Richard Feynman posed the question of whether the gravitational field generated by a mass in spatial superposition is the superposition of the gravitational fields produced by the mass at two separate locations, or if it behaves differently. He leaned towards the first option, while acknowledging the possibility that quantum mechanics might fail under certain conditions. Despite over 60 years of intensive theoretical and experimental research, this question remains unanswered. We examine the current state of theoretical and experimental studies and propose new ideas for testing the quantum nature of gravity.

Although theoretically, quantum gravity is much studied, it has no empirical evidence yet. This makes ``is gravity quantum?" one of the most important open questions of our time. I have pioneered an ambitious idea ``spin entanglement witness for quantum gravity," to test the quantum nature of gravity in a lab with my collaborators. It exploits quantum information ideas and combines a quantum spin with cooling/trapping quantum technologies. It is based on entangling two neutral quantum masses solely by their gravitational interaction while all other interactions are mitigated, e.g. electromagnetic (EM) interactions between the masses. It proves the quantum nature of gravity, as classical gravity cannot mediate quantum correlations (entanglement). The potentially realizable protocol requires meeting a rich set of challenges: mitigating the EM interactions and background, creating spatial quantum superpositions for massive objects, and measuring spin correlations to witness the entanglement. We must also protect the quantum superpositions from heating, blackbody radiation, acceleration, seismic and gravity gradient noises.

We present our development of a table-top quantum sensor with femtometer sensitivity within the acoustic frequency band. Our sensor utilises the expertise developed within the gravitational-wave community, particularly in the control of high-finesse, suspended interferometers, and the mitigation of seismic and thermal noise. We construct a system consisting of a cryostat-mounted four-stage suspension supporting two cavities with optical finesse in excess of 350,000. We use active isolation of the entire cryostat system to achieve an order-of-magnitude of reduction of the seismic noise prior to the passive isolation of the internal suspension. We achieve the femtometer sensitivity using a custom-made phase lock loop. With further enhancements to the readout electronics and suspension characteristics, we aim to reach the quantum radiation pressure noise. This sensor holds the potential for future applications in demonstrating macroscopic entanglement and testing semi-classical and quantum gravity theories.

We investigate the sensitivity limits of a near-surface quantum sensor that utilizes a two-level atom as a probe at distances in the range of 10-100 nm from a surface through the fluctuation-induced Casimir-Polder interaction. We demonstrate that surface-mediated coherence can be preserved for a longer duration under specific conditions compared to a free-space scenario. As a result, the quantum Fisher information (QFI) is enhanced in the presence of the surface, leading to increased measurement precision. We show that these conditions depend on the geometry, material properties of the surface, and the atom-surface distance. Additionally, we examine the QFI for different surface materials as a function of distance and extend our model to a multi-atom system, demonstrating how surface-mediated correlations further enhance QFI and enable high-precision quantum sensing. Our findings have significant implications for understanding sensing in confined geometries and offer a practical protocol for nanotechnology applications.

Numerous real-world applications, such as in civil engineering1, inertial navigation2, and Earth Observation3, have demonstrated the utility of quantum sensing with atom interferometers. Today, the biggest challenge to broader market adoption of these sensors is the indepth knowledge of quantum mechanics required by both the manufacturers and users of these devices. We aim to make the design, construction, and operation of atom interferometers more intuitive using software that incorporates our years of experience in atom interferometry simulation. Here, we provide an overview over our simulation capabilities. Our versatile numerical toolbox enables efficient simulation of atomic test masses interacting with realistic electromagnetic, gravitational and optical forces, as well as prediction of sensor performance in realistic deployment scenarios, e.g., on air, land, and water vehicles.

We investigate the interplay between modes and particles in determining quantum precision limits, focusing on parameter estimation with single photons distributed over continuous degrees of freedom, such as the frequency of light. We demonstrate that frequency can be treated similarly to quantum optical continuous variables, like field quadratures, and that frequency-entangled states achieve the same precision scaling with photon number as single-mode states. We emphasize the importance of collective variable measurements, such as average frequency, and analyze recent experiments in light of our findings. Our results reveal that the maximum achievable precision is determined by the interplay between particle and modal properties (light and color). Additionally, we propose a two-photon interference experiment that illustrates our conclusions, achieving the best observed ratio between experimental precision and the theoretical ultimate quantum precision limit.

Photon statistics offer valuable insights into the quantum properties of light. This information can be utilized for advanced imaging, communications and computing applications. However, as most single-photon detectors contain only one or a few pixels, the scale of these measurements had been restricted. Advances in nano-electronics have recently led to the fabrication of the SwissSPAD3 (SS3), a large-scale single-photon avalanche detector (SPAD) array. The SS3 features a 500x500 pixels SPAD array with low dark-counts rate and global temporal gating options. In this study, we use the SS3 to perform wide-field sensing of photon statistics within a fluorescence microscopy setup. The system design, calibration process and experimental results will be presented, and potential applications will be discussed.

We present a modulation-transfer method to in- crease the detection bandwidth of the Rydberg RF receivers based on three-level Electromagnetically Induced Transparency (EIT) in Rubidium vapor. In this scheme, we phase-modulate the coupling laser to generate sidebands. The nonlinear wave- mixing in the atomic ensemble transfers the modulation from the coupling to the probe laser. The beat note detected in the probe laser intensity provides a new detection response to the RF field. The recorded results show a higher detection sensitivity to the detuned RF field, thus extending the bandwidth of the detector.

MXene is an emerging category of two-dimensional (2D) material with remarkable physicochemical properties, including outstanding photothermal conversion capabilities and fluorescence emission. Understanding fundamental mechanisms underlying these optical properties is critical for the development of innovative optical devices for diverse applications in photonics and quantum technologies. Here, we present a unique approach to investigating the fundamental quantum optical phenomena in MXene using fiber Bragg grating (FBG) technology. The FBG coated with MXene displays distinctive Bragg wavelength shifts when subjected to different excitation photon energies across a wide range of wavelengths from 365 nm to 600 nm. The results indicate energy-dependent excitonic transitions resulting from light-matter interactions. Furthermore, our findings demonstrate the detection of these quantum transitions at 100 microwatts of incident photons on the FBG. This innovative method of probing the quantum optical phenomena of 2D materials using FBG has the potential to offer next-generation quantum applications.

Quantum imaging with undetected light (QIUL) is a technique with great potential for imaging applications where extreme wavelengths are required to illuminate the object and, in particular, when low light intensities are crucial to not damage or modify the sample under study. This technique is based on the concept of induced coherence and makes use of spatial correlations. Therefore, either momentum or position correlations can be exploited by constructing a suitable system to access them. Depending on the selected configuration, image resolution is differently governed by the parameters of the quantum imaging source, e.g. crystal length, pump waist, and the down-converted wavelengths. Here, we present a tool to optimize the resolution limit of the imaging system given a specific application.

Quantum imaging is a research area that seeks to produce “better” images using quantum methods. The image can be better in one of several different ways. It might possess better spatial resolution, it might display better signal-to-noise ratio, or it might be able to be formed using a very small number of photons. From an operational standpoint, we can consider quantum imaging to be an imaging modality that seeks to exploit the quantum properties of the transverse structure of light fields. In this presentation, we describe several different recent examples of advances in the field of quantum imaging.

Adaptive optics has revolutionized imaging in fields ranging from astronomy to microscopy by correcting optical aberrations. However, disturbances often become too strong and fall into the scattering regime. Despite the proven resilience of high-dimensional entangled quantum states against noise, these states still encounter challenges when attempting to freely traverse scattering media, necessitating correction for their utilization in quantum protocols. We report the first experimental realization of focusing a high-dimension two-photon entangled state through a scattering medium using wavefront shaping algorithms using a photon coincidence feedback. Compared to other studies, the presented method doesn't require any classical light to work. To achieve that, we studied theoretically the modulation of the spatial coincidence rate with respect to the modulated phase and provided a full description of it. An interesting behavior appears as the coherent classical light remains scattered and uncorrected, underscoring the remarkable potential of these techniques in quantum communication and imaging.

We successfully miniaturized a quantum interferometer module to a footprint of 80 x 60 mm². The module included a 660 nm pump laser, a ppKTP crystal for spontaneous parametric down conversion, a 3.8 µm MIR free space emission port to the device under test and a NIR fiber port to connect to a NIR spectrometer with a wavelength span near 800 nm. A quantum interference signal with a visibility of more than 55% could be obtained from a mirror surface. We aim to integrate the module in a full MIR quantum OCT scanner system in the near future.

We introduce a quantum imaging microscopy technique using radial polarization imaging with entangled idler/signal photons to measure birefringent micropatterns. Using a radial wave plate that converts linear polarizations to radial, the signal photons in radial polarization states are imaged at an intensified single-photon camera triggered by the idler photons that have interacted with the birefringent material of the pattern. From the single-frame coincidence images, the local birefringence properties are extracted, enabling phase mapping over the pattern. Our imaging technique may open new avenues for real-time remote measurements of dynamic birefringence.

High dimensional cluster states are required for error correction in quantum computing. We generate 4-dimensional optical frequency-mode cluster states using a simple 4-wave mixing system in Rb atomic vapor. In our experiment, the operational quantum bits, or qumodes, are created with an electro-optic modulator, which functions as a beam splitter in the frequency domain. We demonstrate how qumodes are connected through different modulation dynamics.

Entanglement is a powerful resource for improving the precision of quantum measurements. All-to-all entanglement that is naturally generated by long-range interactions in optical cavities is optimally suited to single parameter estimation tasks, such as timekeeping or sensing global fields. In our system, we combine global cavity-mediated interactions with local rotations to create multimode entangled states that are useful for a wider variety of quantum sensing tasks. As a specific example, we produce a two-mode squeezed state (EPR state). By treating one subsystem as a sensing region and the other as an ancilla or quantum memory, we achieve simultaneous sensitivity to displacements of two conjugate quadratures in the sensing region. Using an echo-based protocol, we simultaneously read out both quadratures with a sensitivity surpassing the local Heisenberg limit. This simultaneous sensitivity to conjugate displacements promises a provable speedup for sensing tasks such as characterizing bosonic random displacement channel. Our general method is scalable to larger and more complex graphs, laying groundwork for advanced quantum metrology protocols such as quantum compressed sensing.

Quantum enhanced multiparameter sensing is receiving great attention for its applications to vector sensing, imaging, sensor arrays, and clock networks. While for single parameter sensing, a clear theoretical framework has been developed, multiparameter sensing is surprisingly complex from a conceptual point of view. In this talk I will present our proof-of-principle experiment in multiparameter quantum enhanced sensing with a spatially separated array of entangled 87Rb atomic sensors. The production of these entangled sensors and flexible manipulation of the entanglement to optimize the sensor’s sensitivity will be described. Some of the conceptual questions regarding multiparameter sensing will also be addressed.

We generate quantum correlations between two bright beams of light using four-wave mixing, resulting in intensity squeezing. This intensity-squeezed light is applied to enhance sensing and imaging of electronic devices. Our current focus also includes the development of low-frequency squeezing for advanced sensing and communication technologies. In this presentation, I will share recent experimental results from our lab on the generation and application of intensity-squeezed light in these contexts.

Quantum enhanced measurements depend on generation of squeezed light with quantum fluctuations below standard quantum limit. Precise spatial information about squeezed modes is crucial to reach maximum quantum advantage in sensing applications. Yet the mixed mode squeezed vacuum (the extreme case of squeezed light) is particularly elusive for such characterization. We will present our method, based on the structured light homodyning, to extract squeezing levels and mode shapes from a multimode quantum squeezed vacuum beam.

Squeezed light has been instrumental in the sensitivity of gravitational-wave interferometers since 2018. We present an experiment that aims to translates this technique in the micromechanical domain, with a broadband displacement measurement of an optomechanical sensor, with a sensitivity beyond the Standard Quantum Limit. The optomechanical sensor is a 100-nm thick phononic-crystal SiN membrane, embedded in a high-finesse fiber optomechanical cavity in a dilution fridge. Displacement sensitivity beyond the SQL will be achieved with a frequecy-dependent squeezed light source, based upon a sub-threshold Optical Parametric Oscillator, combined with a single-ended filter cavity. Current progress of the experiment on the optical, squeezing and mechanical fronts will be discussed.

Quantum states of light called "squeezed light" are an essential resource in cutting edge experiments, such as the LIGO gravitational wave detectors, and in continuous variable quantum computing and quantum communications. While the use of squeezed light has been clearly demonstrated through its enhancement of the LIGO detectors, to date, most squeezed light sources capable of generating large degrees of squeezing consist of free-space optics spanning one or more optics tables. We present a compact, modular, and movable source of squeezed light which will allow future experiments to take advantage of squeezed light as a quantum resource while minimizing the space and cost required to deploy high levels of squeezing. This device produces more than 6 dB of measured squeezing and is easily transportable and occupies only a small fraction of an optics table – its footprint is about 45 cm by 45 cm. This device promises to extend the types of measurements that can benefit from squeezed light in practice, just as the advent of commercial lasers greatly expanded the use of those devices in the past century.

We explore the use of a spatial mode sorter to image a nanomechanical resonator, with the goal of studying the quantum limits of active imaging and extending the toolbox for optomechanical force sensing. In our experiment, we reflect a Gaussian laser beam from a vibrating nanoribbon and pass the reflected beam through a commercial spatial mode demultiplexer (Cailabs Proteus-S). The intensity in each demultiplexed channel depends on the mechanical mode shapes and encodes information about their displacement amplitudes. As a concrete demonstration, we monitor the angular displacement of the ribbon’s fundamental torsion mode by illuminating in the fundamental Hermite-Gauss mode (HG00) and reading out in the HG01 mode. We show that this technique permits readout of the ribbon’s torsional vibration with a precision near the quantum limit.

Quantum illumination theoretically promises exponentially higher resolution of object images. This research characterizes the effects of turbulence on the ability to successfully resolve an object image using entangled photons within the optical regime. Ultimately, this research better quantifies the fundamental scientific challenges that must be overcome prior to the development of an operational quantum illumination system and makes recommendations regarding potential solutions.

Photon-pair correlations in spontaneous parametric down conversion (SPDC) processes are ubiquitous in quantum photonics. In this work, we engineer these correlations by imaging arbitrarily chosen objects in the second order correlations of spatially-entangled photon pairs produced by type-I SPDC in a non-linear crystal. Our approach is effective with both amplitude and phase objects, even when the beam intensity is spatially shaped. Additionally, we show that it is resistant to scattering by applying wavefront shaping techniques. We also find that certain phase patterns can refocus through the scattering medium exclusively with photon pairs, and not with classical coherent light. Consequently, the transmission of an image through the scattering medium is only possible if it is correlation encoded; coherent light alone cannot reconstruct the image. Our approach enables the transmission of complex, high-dimensional information using quantum correlations of photons, offering significant potential for advancing quantum communication and imaging protocols.

We recently demonstrated a nonlocal form of Mueller polarimetry using the polarization correlations of polarization-entangled photons. Classical Mueller polarimetry consists of determining the optical properties of a sample by sending light in a certain number of polarization states and doing polarimetry of the light emerging from the sample for each case. From the input and output Stokes parameters, one determines the Mueller matrix, which contains the polarization properties of the sample. The nonlocal method relies on the correlations of photons in an entangled state, such that polarization projections on one photon not interacting with the sample serve, via correlations, to specify the state of the partner photon incident on the sample. The correlation is completed by projecting the state of the light after the sample and recording coincidence detections. In this study, we investigate the effects of imperfections in the entangled state and quantum statistics on the Mueller matrix that is obtained.

We present a 3D quantum enhanced microscope which utilizes the principles of quantum ghost imaging (QGI) to produce volumetric images. This tool is developed to address current challenges in 3D microscopy which include the volumetric capture and tracking of photosensitive samples. Much of the active research on QGI are focused on exploiting the correlative behaviors of the quantum light sources, to obtain higher dimensional data than can be achieved with traditional imaging; in this vein, our study is similar. Where we believe our approach deviates, even from current research in QGI, is that we demonstrate that perpendicularly scattered light from the sample can still be correlated to generate a ghost image from a different perspective plane. Using two state-of-the-art single photon avalanche diode (SPAD) array detectors, this achievement allows us to generate, for each count, positional coordinates from two perpendicular planes. We present this novel 3D QGI approach along with initial 3D images of silver nanoclusters, followed with a discussion on how the results can impact biological imaging applications. Prepared by LLNL under Contract DE-AC52-07NA27344

By taking advantage of quantum phase estimation measurement, we demonstrate optical phase stabilization and phase tracking of metropolitan scale quantum network links with the faintest states of coherent light reported to date and at the photon flux comparable with quantum payload. In comparing Fisher Information, our phase estimation protocol yields higher precision, than homodyne and heterodyne phase measurements. This method successfully stabilizes a 120 km deployed network link. In addition, we show that in these practical settings and with non-ideal components, on average, our stabilization/tracking protocol beats the ideal classical measurement-based stabilization. Obtaining stable optical phase stabilization between quantum network nodes is crucial for protocols like entanglement swapping and quantum repeaters.

Optically interfaced solid-state spins enable quantum technologies with unprecedented capabilities for sensing, communication, quantum-coherent memories, and exploration of fundamental physics. Hexagonal boron nitride (h-BN), a wide-bandgap semiconductor that hosts numerous species of optical defects, is especially promising for its low-dimensional morphology that facilitates efficient photon collection and device engineering advantages compared to three-dimensional crystals. In this work, we investigate an emitter in h-BN that exhibits single-photon emission and optically detected magnetic resonance (ODMR) at room temperature and simulate its ODMR spectrum using Lindblad master equations and density matrices. We compare our simulation with recent experimental data, determining the rates and coherence times that govern its optical and spin dynamics. This work was supported by NSF DMR-1921877.

We analyze the capability of a deterministic photon subtraction in generation of non-classical pulses of light with application to sensing and metrology. The device comprises a Λ-type emitter coupled to a bimodal cavity system with waveguide coupling. First, a photon transport analysis is conducted to analyze the frequency response of the system and study the impact of various physical parameters on it. Subsequent analysis combines the Monte-Carlo method with the SLH framework of input-output formalism to numerically verify the analytical findings as well as to calculate the state of the output pulses of light. Our findings highlight the potential of utilizing insights from single-photon transport analysis to guide the design of efficient photon subtractors capable of extracting photons from input pulses with varying photon counts and generation of non-classical light pulses with a high success probability.

The Nitrogen-Vacancy (NV) centers in diamonds are one of the most interesting systems with widespread potentialities for applications to quantum sensing. In this talk, I will report a few recent results concerning technical improvements in ODMR measurements at micro/nanoscale level and applications to cell metabolism studies.

We propose a weak measurement scheme using nonlinear interferometry to amplify phase shifts in optical waves. Parametric amplifiers serve as nonlinear beam splitters, enhancing phase signals by the amplification gain while maintaining low quantum noise. This method promises improved signal-to-noise ratios beyond standard limits, despite some sensitivity to internal losses.

The nitrogen-vacancy (NV) center in diamond is a promising candidate for advanced quantum sensing technologies due to its unique properties. The fabrication of high-performance NV center based sensing devices requires not only precise control over the NV concentration but also the use of isotopically purified diamond material. This study focuses on the fabrication of isotopically purified NV diamonds using a combination of Chemical Vapor Deposition (CVD) and post-growth processing of the diamond material. In this unique approach, spin control techniques utilizing the NV centers themselves are used to provide insight into the atomic composition of the created diamond material. Reliability and reproducibility of the created NV centers and the underlying diamond material are of high importance to enable the use of such materials in real-world products.

LIDA, the Laser Interferometric Detector for Axions, is a resonant cavity experiment searching the neV mass scale of axion-like dark matter in the galactic halo. We present the development of the free-space squeezed vacuum source for quantum enhancement of LIDA beyond the shot noise limit. Similar to gravitational wave detectors, we utilise a linear cavity for second harmonic generation of 1064nm and a bowtie cavity for squeezed vacuum generation via optical parametric oscillation. Both cavities include ppKTP crystals and a coherent control field to control the squeezing angle. We demonstrated squeezing at 0.5MHz and now build a compact squeezer for injection into LIDA with the aim of 10dB of squeezing. The mode mismatch between squeezed field and resonant field in the interferometer is one of the sources of optical loss that affect the squeezing; our research is also aimed at developing low-loss deformable mirrors to maximise the injection efficiency.

We are developing an entanglement-enhanced approach to improve the sensitivity and robustness of atomic force microscope (AFM) measurements. Traditional AFM methods rely on classical sensors such as classical optical interferometers or position-sensitive detectors to measure movements of the AFM cantilever. Interferometric sensors, in particular, can be susceptible to optical loss and background light interference and may require high illumination power to compensate. Our method instead employs two-photon quantum interference with highly non-degenerate frequency-entangled photon pairs at 810 nm and 1550 nm, achieving nanometer-scale sensitivity with robustness against background and loss. Our quantum sensor may be used to enhance the monitoring of nanometer-scale cantilever displacements.

We demonstrate a method for timing light pulses with an accuracy surpassing that of superconducting nanowire single-photon detectors (SNSPDs) or conventional avalanche photodetector (APD) timing jitter. Our technique involves using a nonlinear crystal to perform frequency conversion between the signal (quantum or classical) to be detected (e.g., a 1-ps long pulse at 1560 nm) and a chirped escort pulse (e.g., at 780 nm). Because the energy of the escort photons depend on the precise position along the chirped pulse, we can determine the timing of the signal relative to the original escort by measuring the frequency of the upconverted light; this spectral measurement can be made with detectors that are much slower or have much higher timing jitter than the original signal pulse duration.

Optical coherence tomography (OCT) has gained widespread use due to its non-invasive nature in numerous applications. However, its axial resolution is degraded due to dispersion in the sample and optical system. Quantum optical coherence tomography (QOCT), which utilizes two-photon interference with frequency-entangled photon pairs, has garnered attention as a potential solution to this problem. In this work, we realize QOCT imaging with both axial and lateral resolutions less than 2 µm, corresponding to the highest volume resolution to best of our knowledge. Furthermore, we also demonstrate that high-volume resolution QOCT imaging is possible even under high group velocity dispersion. We believe that this work represents a significant step forward in QOCT imaging of fine three-dimensional structures.

As the High Voltage Direct Current cables constitute the backbone of the newly developed power transmission systems based on renewable energies, it is becoming increasingly important to monitor the integrity of these cables. Here, we propose to monitor the degradation of the cable insulation performance by measuring the current passing through the cable insulation layer, commonly called leakage current. Given the need for a sensitive and galvanically isolated sensor, the current measurement prototype is using a magneto-optical technique, the Zeeman Effect. Due to the many integration challenges, such as limited power consumption, high ambient magnetic noise, or the large range of operating temperature, innovative solutions were needed to develop the sensor. The design of the prototype and the latest laboratory results will be presented.

Efficiently creating dependable triphotons with nonclassical correlations distributed across all three particles has long been a goal in quantum optics. Generating these triphotons directly through one-step high-order nonlinear optical process is crucial in nonlinear and quantum optics, with potential applications in quantum information science and technologies. Here, we conducted the first experiment demonstrating a new method to produce genuine time-energy-entangled W-class triphotons through spontaneous six-wave mixing. By inputting three classical continuous-wave lasers, we observed three spatially separated newborn photons with different colors. These triphotons exhibit strong spectral quantum correlations and can be manipulated to achieve versatile multi-frequency entangled states. Reliable triphoton sources are essential for various quantum information processing applications, providing a quantum advantage.

Here we introduce and experimentally test a novel technique [1] for the reconstruction of multimode optical fields, based on the simultaneously exploiting both the generalized Glauber’s K^th-order correlation function g^((K)) and a recently-proposed anti-correlation function dubbed θ^((K)) [2], proven to be resilient to Poissonian noise. Our experimental results show how this method, although requiring less “a priori” information than other mode reconstruction techniques based only on g^((K))’s [3], steadily outperforms them. Given its versatility and robustness, this new mode reconstruction technique is suited for a widespread use in rereal applications of optical quantum measurement, from quantum information to quantum metrology, especially for characterizing ensembles of single-photon emitters in the presence of background noise (caused by, e.g., residual excitation laser light, stray light or unwanted fluorescence). [1] L. T. Knoll et al., Adv. Quantum Technol. 6, 2300062 (2023). [2] L. Lachman, L. Slodička, R. Filip, Sci. Rep. 6, 19760 (2016). [3] E. Goldschmidt et al., Phys. Rev. A 88, 013822 (2013).

Rydberg-based quantum sensors have recently emerged as a versatile tool for tunable detection of microwave fields. In this work, we present our advancements in sensing millimeter waves (mmWaves) by measuring the increased fluorescence of the intermediate 5P3/2 state in a four-level ladder system of rubidium-85. Capturing the emitted fluorescence allows us to effectively image the mmWave field incident on a plane of atoms in the vapor. We chose 37.073 GHz mmWave which is on resonance with the transition from 40D_(5/2) → 39F_(7/2) transition. We compare the dynamic range of our sensor to simulations, showing good agreement, and utilize this range to detect modulation on the signal, and image one-dimensional mmWave intensity distribution produced by a horn antenna along the length of the cell. Additionally, we demonstrate two-dimensional imaging of the mmWave field as it propagates through an aperture.

In this presentation, we determine the radio frequency (RF) performance characteristics of a Rydberg heterodyne electrometer, a novel atomic-based detection system that leverages the extreme sensitivity of Rydberg atoms to electromagnetic fields. Our study focuses on key figures of merit critical to evaluating RF receivers: the noise temperature, the 1-dB compression point, and the second and third order intercept points. These metrics are crucial for assessing the viability of Rydberg heterodyne electrometers for applications in communication systems and spectral monitoring, providing insights into their operational advantages and limitations relative to traditional electronic receivers. Through experiments and analytical modeling, we quantify the effects of noise and nonlinearity that impact the electrometer’s ability to accurately reproduce input signals at various power levels.

The last ten years have seen increasing interests in Rydberg atoms for applications as electric field sensors, RF spectrometers, and microwave receivers. In this paper, we present our experimental studies of a Cs Rydberg atomic microwave receiver and its temporal response characteristics to amplitude, frequency, and phase shift keying modulations. The receiver is associated with the Cs Rydberg transitions at various frequencies, which are generated by double-resonance laser excitations in a vapor cell. In our work, we use the Electromagnetically Induced Transparency (EIT) and Autler-Townes (AT) effects to directly receive modulated microwave signals and recover the data encoded in the carriers. Modulation depths up to 90% are experimentally observed and studied as a function of the modulation clock frequency. Our modeling shows that Cs atoms have accessible Rydberg transitions at frequencies from below GHz all the way to THz for wideband microwave receiver applications in various RF systems.

Alkali vapor spin systems hold significant potential for quantum sensing applications. We report on the critical behavior of strongly interacting, warm cesium vapor driven by linearly polarized light, where the collective nature stems from local spin-exchange interactions. We experimentally observe the power-law dependence of the macroscopic spin magnetization on both the intensity of the driving light and the gas density, as well as the divergence of the susceptibility to an imbalance in the drive. We identify this phenomenon as a second-order, mean-field, magnetic phase transition and measure the phase diagram of the system. The spin response out of equilibrium – when crossing the phase transition – critically slows down to a level of a few seconds, more than two orders of magnitude longer than the bare 20-millisecond spin lifetime. We thus establish an accessible, well-controlled platform for investigating spatial and out-of-equilibrium properties of Ising-like systems and potentially for advancing the development of quantum sensors based on critical dynamics.

This paper describes the progress made in developing wafer-scale fabrication process of alkali vapor cells for chip-scale atomic devices such as Coherent Population Trapping (CPT) clocks, optical frequency standards and Rydberg-atom-based sensors. The wafer level fabrication process uses anodic bonding and introduces alkali atoms by chemical reactions of Alkali Chloride with Barium Azide. This method is compatible to make cells with a wide range of buffer gas species and pressures, including evacuated cells. We improve the yield of the cells to above 50%. We will show the residual gas pressures for evacuated cells are mostly consistent with zero within the resolution of the saturation absorption spectroscopy measurement. The temperature coefficients for the CPT spectroscopy are improved with Ar-N2 mixture buffer gas compared with only N2 buffer gas.

Here we report on the progress of an iodine-filled Photonic Microcell (PMC). By trapping both I2 and light inside a hollow-core photonic crystal fiber (HCPCF) within small cross-sectional areas over length scales larger than meters, we can have not only high atom-molecule interactions but friendly compactness, room temperature operation, remarkable stability from environmental noise (especially thermal and acoustic). We will present our work on filling and hermetically sealing the PMC for use as a frequency reference. We will also present our results on spectroscopy using this PMC as well as laser stability: 1) sub-doppler (few MHz) features featuring > 1000 signal-to-noise ratios realized with less than mWs of laser power, 2) compact, lightweight, all-fibered design, 3) long lifetimes (years), and 4) the possibilities for an all-fibered optical, compact optical clock perfectly adaptable to extreme conditions - space missions, marine applications, noise environments, etc. Preliminary results show achievable Allan Deviation at 1s well below 10^(-11)!

Atomic vapour cells are an indispensable technique for quantum technologies (QT), but potential improvements are limited by the capacities of conventional manufacturing techniques. Exploiting a 3D-printing technique - digital light processing - we demonstrate an additively manufactured glass vapour cell AM capacities, we demonstrate intricate internal architectures, overprint 2D optoelectronical materials to create integrated sensors and surface functionalisation, while also showing the ability to tailor the optical properties of the AM glass by in-situ growth of gold nanoparticles. The produced cells achieve ultra-high vacuum of 2×10−9 mbar and enable Doppler-free spectroscopy; we demonstrate laser frequency stabilisation as a QT application. These results highlight the transformative role that AM can play for QT in enabling compact, optimised and integrated multi-material components and devices.

To control the motion of a trapped particle and prevent quantum state decoherence, cooling is required. In order to trap particles that do not offer cooling transitions, sympathetic cooling can be used. We are going to investigate the effects that arise from changing the trapping waveform applied to a Paul trap. We are especially interested in the comparison of the sympathetic cooling performance of the sinusoidal wave with its alternatives. We investigate different waveforms such as normal sine driven traps, but also traps driven with a saw-tooth, triangle, or square waveforms. From the simulation results, cooling rates as well as stability parameters are extracted. Ours findings indicate potential benefits of further in-depth studies on the key properties that trap driving waveforms should possess to enhance the sympathetic cooling efficiency in Paul traps.

Gravity gradient map matching has emerged as a promising alternative method for navigation, particularly in environments where traditional systems face limitations. The technique leverages variations in the Earth's gravitational field to measure gravity gradients, providing unique signatures for different locations. By employing sophisticated algorithms for map matching, the measured gravity gradient can be compared with a pre-existing reference map, enabling precise localization, which can provide direct information or alternatively can exploit the high measurement stability of quantum sensors as drift correction for inertial navigation systems. Unlike conventional methods such as GNSS, gravity gradient map matching is less susceptible to signal disruptions in challenging environments like urban metropolises, dense foliage, or underwater, offering enhanced accuracy and reliability. This presentation will describe recent progress towards platform operation of gravity gradient quantum sensors for navigation applications.

The transition from classical physics to quantum mechanics remains mysterious. In classical electrodynamics, the electron's magnetic dipole moment is described by the Bloch equation. Notably, Majorana formulated this equation 14 years before Bloch's 1946 publication, applying it to an atom, while Bloch considered it valid for only macroscopic magnetization. The author suggests renaming the Bloch equation to the Majorana-Bloch equation. Since neither Majorana nor Bloch, nor existing literature, provide a derivation, we offer our own using two models. We then mathematically convert the classical Bloch equation for electron spin to the space-independent von Neumann equation for a pure two-level spin system. Additionally, we derive the space-independent Schrödinger–Pauli equation within quantum mechanics and co-quantum dynamics frameworks. Thus, we establish the inverse conversion and the two-way transitions for a pure state of electron spin between the classical Bloch equation and the space-independent Schrödinger–Pauli equation.

We present a quantum optical pattern recognition method for binary classification tasks. Without direct image reconstruction, it classifies an object in terms of the rate of two-photon coincidences at the output of a Hong-Ou-Mandel interferometer, where both the input and the classifier parameters are encoded into single-photon states. Our method exhibits the same behaviour of a computational neuron of unit depth. Once trained, it shows a constant O(1) complexity in the number of computational operations and photons required by a single classification. This is a superexponential advantage over a classical neuron, that is at least linear in the image resolution. We provide simulations and analytical comparisons with analogous neural network architectures.

Quantum control is a fundamental tool for quantum technologies, and quantum Zeno (QZE) and anti-Zeno (AZE) effects, respectively denoting the slowdown and speedup of quantum system evolution by frequent interruptions/operations, represent quantum control paradigms. Indeed, they allow either protecting (QZE) or steering (AZE) the state of a quantum system via the interplay between frequent operations (system control) and the coupling of the system to its environment. Here we present two experiments demonstrating the possibility to exploit QZE and AZE to extract information on noise processes occurring in a quantum channel. In the first experiment, we realize the first noise diagnostics scheme based on repeated quantum measurements, showing how a single photon undergoing a noise process (in our case, random polarization fluctuations) can quantify non-Markovian temporal correlations within such a noise. In the second experiment, we show how a QZE-protection mechanism applied to a quantum state can become a noise sensing technique, allowing to estimate the statistical distribution of decoherence effects occurring on a photonic qubit during its propagation in a noisy quantum channel.

Here, we present a route to achieve near ground state cooling of all motional modes using the same lasers and transitions to eventually bring the ions very close to their motional ground states by sideband cooling. Based on a past study of Doppler cooling of Ca^+ ions on a dipolar forbidden transition, we have recently theoretically looked more careful into strategies for more optimizing such cooling schemes for Ba^+ ions in the near future, applying muliti-watt lasers to drive the 2^S_1/2 – 2^D_3/2,5/2 transitions. Besides for many quantum technology applications of trapped ions leading to a much-reduced laser infrastructure, the presented cooling scheme enables complete background-free optical qubit readout in the blue-green through two-photon excitation in the orange and infrared.

Phase estimation is crucial to quantum-information processing. Several quantum algorithms use phase estimation as a subroutine for finding unitary operators’ eigenvalues. Furthermore, phase estimation is used in quantum metrology, the field of using quantum systems to probe, measure, and estimate unknown physical parameters. I will tackle the problem of how to measure the strength of a totally unknown unitary. Imagine a unitary rotation generated by a magnetic field. If the direction of the magnetic field is unknown, no strategy with classically separable probes enables optimal measurements of the rotation angle. However, a quantum strategy, relying on entanglement, does. Our strategy leverages quantum simulations of hypothetical closed timelike curves (CTCs) to overcome limitations in phase estimation. Colleagues and I demonstrate this on a superconducting processor. I will describe how our technique can be used in tasks ranging from sensing to quantum-computer calibration. Further, I will discuss extensions and applications of our agnostic phase-estimation protocol. [1] PhysRevLett.132.260801 [2] PhysRevLett.131.150202

We present the design and initial results of a stellar intensity interferometer using small 0.25 m Newtonian-style telescopes in an urban backyard setting. Using Sirius as a target star, which yields 2.0 Mcps per detector with matched 1 nm wide filters at 589.6 nm, we obtained a strong second-order correlation spike with an SNR > 10 (FWHM width of 310 ps) after 13.5 hours of integration over a three-night period. The maximum baseline of the telescopes was 3.3 m. Our optical system allows for on-axis guiding and tracking of the star, keeping it centered on a 100 µm diameter fiber optic cable, which ensures a steady detector count rate throughout the evening. Future work includes collecting data with other baselines and bright stars while using a lower jitter setting on our time-tagger (26 ps vs. 140 ps FWHM).

The use of spontaneous parametric down-conversion and quantum interference allows for the measurement of mid-infrared radiation, relying on near-infrared emitting laser sources and near-infrared detection equipment only. To utilize this advantageous "sensing with undetected photons" technique in practical mid-infrared spectroscopy, miniaturization is of paramount importance, particularly for applications outside of laboratory settings. In this study, we present a quantum light source with a footprint of less than a cell phone and give insights to its optical concept and its micro-manufacturing. We demonstrate photon-pair rates of ≈ 10⁹ s⁻¹ and present application concepts for sensing of micro-plastics in aqueous solutions.