We describe a technique whereby a coherent amplitude can be imprinted nonlocally on to a beam of light with thermal statistics that has no phase information on average. We have successfully performed the first experimental realisation. The technique could have applications in the sharing of quantum information and in covert quantum imaging scenarios.

We demonstrate the possibility of generating non-Gaussian states of light by exploiting a setup fully based on plug-and-play guided-wave components from classical telecom and non-linear optical technologies. Our scheme relies on heralded single photon subtraction from single mode squeezed states generated in a single-pass configuration in nonlinear optical waveguides and allows generating Schrodinger kitten quantum optical states. We discuss the different parameters affecting the shape of obtained states by comparing the theory and the numerical simulations.

Lithium-niobate-on-insulator (LNOI) is emerging as a promising platform for integrated quantum photonic technologies because of its high second-order optical nonlinearity, compact footprint, and low propagation loss in a broad wavelength range. Importantly, LNOI allows for creating electro-optically tunable circuits that can be efficiently operated at cryogenic temperature. Their integration with superconducting nanowire single-photon detectors (SNSPDS) paves the way for realizing scalable photonic devices for fast manipulation and detection of quantum states of light. Here we report the monolithic integration of these two key components in a low loss (0.2 dB/cm) LNOI waveguide network. As an experimental showcase of our technology, we demonstrate the combined operation of an electrically tunable Mach Zehnder interferometer–an essential building block for the realization of reconfigurable optical networks-and two waveguide-integrated SNSPDs at its outputs. We show static reconfigurability of our system with a bias-drift free operation over a time of 12 hours, as well as high-speed modulation at frequencies up to 1 GHz.

Long optical storage times are an essential requirement to establish high-rate entanglement distribution over large distances using memory-based quantum repeaters. Rare earth ion-doped crystals are arguably well-suited candidates for building such quantum memories. Toward this end, we investigate the 795.32 nm ³H₆ ↔ ³H₄ transition of 1% thulium-doped yttrium gallium garnet crystal (Tm³⁺:Y₃Ga₅O₁₂ : Tm³+:YGG). Most essentially, we find that the optical coherence time can reach 1.1 ms, and, using laser pulses, we demonstrate optical storage based on the atomic frequency comb (AFC) protocol up to 100 µs. In addition, we demonstrate multiplexed storage, including feed-forward selection, shifting, and filtering of spectral modes, as well as quantum state storage using members of non-classical photon pairs. Our results show that Tm:YGG can be a potential candidate for creating multiplexed quantum memories with long optical storage times.

We study a class of receiver-device-independent quantum key distribution protocols based on a prepare-and-measure setup which aims to simplify their implementation. The security of the presented protocols relies on the assumption that the sender, Alice, prepares states that have limited inner-products. Hence, Alice’s device is partially characterized. There is no explicit bound on the Hilbert space dimension required. The receiver’s, Bob’s, device demands no characterization and can be represented as a black-box. The protocols are therefore immune to attacks on Bob’s device, such as blinding attacks. The users can generate a secret key while monitoring the correct functioning of their devices through observed statistics. We report a proof-of-principle demonstration, involving mostly off-the-shelf equipment, as well as a high-efficiency superconducting nanowire detector. A positive key rate is demonstrated over a 4.8 km low-loss optical fiber with finite-key analysis.

We present an experimental implementation of a joint classical/quantum transmission architecture over 10km of SMF with shared hardware at the emission and using a 64-QAM probability shaping modulation format on the quantum channel. We report a mean excess noise measurement of 0.0212 shot-noise units (SNU) on the quantum channel, leading to a secret key rate of 19.5 Mbps when taking into account finite-size effects, while no errors are accounted for on the classical channel. Thus we show that the classical data can provide solid estimates for the phase and frequency recovery of the quantum channel without adding excess-noise above the null key rate threshold. This enables us to perform CV-QKD protocols without dedicated reference signals and paves the way towards hybrid classical and quantum communication protocols.

The present paper shows possible ways to design monolithic Quantum Random Number Generators (QRNGs) in a standard CMOS technology. While all commercial QRNGs based on SPAD technology use an external light as main source of entropy, in the present implementation silicon-based photon sources are used. This approach allows the integration of monolithic QRNGs paving the way towards miniaturized and low-cost devices. Moreover, being the QRNG realized in a standard CMOS technology, in perspective, it can potentially be embedded in secure microprocessor. In the paper we show that the proposed approach is compact, produces a minimum event rate of about 1kHz, possibly extended in case of the implementation of multi-QRNGs working in parallel.

In this work, we study the generation of non-Gaussian quantum states of light using multimode quantum resources. We first propose a theoretical framework to describe photon subtraction operation - a well known non-Gaussian operation - applied to a multimode Gaussian state. We apply this framework to the case of Schrödinger kitten state generation using a multimode squeezed vacuum as input state. We show that a monomode non-Gaussian state with high purity can be generated by a better choice of the different experimental parameters. Then, we propose a new protocol to generate high amplitude non-Gaussian states using spectral multiplexing of input states and Gaussian operations. We show that this protocol can implement the cat breeding operation with less complexity. We show also that this protocol can be used for the generation of approximated GKP state.

We demonstrate a new approach for creating deterministic photon-photon interactions for optical quantum engineering, based on a single-ended medium-finesse optical cavity containing a mesoscopic atomic ensemble. This ensemble is made transparent by a laser beam mapping intracavity photons into Rydberg polaritons. The transparency vanishes when the cloud, acting as a single collective two-level "superatom" with an enhanced coupling to light, is driven from the ground to a Rydberg state. We observe collectively-enhanced Rabi oscillations between these states, optically discriminate them in a single shot with a 95% effciency, and show that a change between the two internal states of the superatom induces a π phase rotation on the light reflected off of the cavity. These ingredients form a complete set of tools for implementing deterministic photonic entangling gates and for generating highly non-classical light without the need for a low-volume high-finesse cavity.

A high imaging resolution or a tight focus of a laser beam imposes a certain minimal numerical aperture (NA) of the optical system. Macroscopic high NA lenses constraint strongly the spatial organization of experiments, in particular when imaging or trapping cold atoms inside a vacuum chamber. Multimode fibers, in conjunction with spatial light modulators, offer an interesting alternative to high NA lenses. Indeed, they are flexible optical waveguides with very small transverse dimensions (∼ 100 μm), and reasonably high NA (up to 0.5). For those reasons, the use of multimode fibers for imaging or laser manipulation purposes has been widely studied in the past years. Here, we transfer these techniques to the field of cold atoms with a multimode fiber forming a compact optical bridge between the inside and the outside of an ultra-high vacuum chamber. We manipulate atoms with laser beams produced through the fiber by digital optical phase conjugation with a spatial light modulator. We are able to transport a small cloud of cold rubidium atoms with a moving optical lattice at about 200 μm from the fiber tip. We can then load them in small optical tweezers with a waist of 1.2 μm. By characterizing the propagation of light modes inside the fiber, we numerically invert its transformation and we reconstruct absorption images of the trapped atoms with a resolution of approximately 1 μm. These results pave the way towards the efficient use of multimode fibers in spatially constrained quantum technology platforms relying on cold atoms.

Quantum photonic integrated circuits (PICs) exploit the virtually null photon-photon interaction to realize systems that are robust to external disturbance. While this resilience is particularly interesting for a development towards room-temperature systems, many experiments rely on superconducting nanowires that need cryogenic temperatures to operate. For photons in the near infrared spectral region, single photon avalanche diodes (SPADs) could be used as a room temperature alternative.

We show a novel method of PIC-detector coupling that allows for the monolithic fabrication of substrate-integrated photodiodes and a silicon nitride PIC on the same chip. With the use of an engineered wet-etching process, we shape the bottom cladding of the photonic layer into a basin with shallow wedge borders on top of the region of the detectors. In this way, the waveguides are gently laid on top of the detectors, allowing for a strong waveguide-detector optical coupling. We show experimental results of the first PIC-diode coupling with a total efficiency exceeding 40%, and the first promising results concerning the coupling with SPADs paving the way for on-chip, room-temperature, single photon detection.

For the adoption of QKD to grow, much effort has been devoted to making QKD systems more robust and efficient. Much of the complexity of a QKD system stems from its transmitter where quantum states encoded with bit values are prepared. Recently, optical injection locking (OIL) has emerged as a promising method to realize high-speed QKD transmitters with a compact design. This approach enables direct phase encoding without the need for external modulators, while simultaneously improving the laser characteristics. Due to these remarkable advantages, OIL has been widely applied to many QKD protocols, including BB84, MDI-QKD and TF-QKD. However, in practice, tuning the laser system to find optimal operating parameters is a very challenging task. This is because the underlying laser dynamics are rich and involve a complex interplay between multiple control parameters. It is therefore highly desirable to develop an efficient method to optimize the systems. Here, for the first time, we address this issue by demonstrating a self-tuning QKD transmitter by implementing a genetic algorithm to autonomously locate the optimum system parameters. Without any user intervention, our approach manages to optimize the quantum bit error rate down to ~2.5%, matching the state-of-the-art performance.

Miniaturization of laser sources is crucial to the translation of quantum technologies from the laboratory to the real world. Typically, the lasers required for cooling and trapping of atoms and ions make up a significant footprint of the measurement system. Increasing robustness and reliability whilst removing noise sources is a key challenge whilst reducing volume. Direct generation GaN based external cavity diode lasers offer lower SWaP-C compared to traditional frequency doubled alternatives. Butterfly packaged single frequency sources operation in the blue-UV allow numerous atomic transitions including Sr, Sr₊, Yb, Yb₊, Mg and Ca to be targeted.

The extreme sensitivity of quantum magnetometers enables new applications in material testing such as the identification of single defect events in the bulk of small volume specimen (0.1 mm³). Exposing ferromagnetic materials to strain alters their magnetic response. Due to uncompensated spins, defects arising from the fatigue process interact with magnetic domain walls. Optically pumped zero-field magnetometers (OPM) provide the sensitivity required to measure small variations in the magnetic response and potentially to quantify damage in the material. We provide first results of a novel micro fatigue setup with an integrated OPM to correlate variations of the magnetic response in a multimodal approach. The position of the Villari reversals within the magneto-mechanic hysteresis and the amplitude of magnetic field are potential candidates to estimate fatigue damage within the specimen.

For examining QKD systems for sustainability to the “backflash” attack, it is necessary to measure the probability of photon re-emission and calculate the maximum possible probability of backflash for the secret key to remain secure. In this paper, we present research on backflash probabilities dependencies on parameters of fiber-based QKD systems. The SPAD gate width for each QKD system and quantum communication protocol is individual, therefore, it is necessary to consider the dependence of the probability of photon re-emission on the SPAD gate width. Moreover, as a result of Laser Damage Attack, active elements, such as a variable attenuator or a pulsed laser, may not work quite stable, eventually, as far as the mean photon number per pulse (μ) varies within a small range, the maximum backflash probability can fluctuate. We demonstrate an experimental setup of correlation “backflash” measurements by optical reflectometry with very low dark count rate and parasitic noise, furthermore, the contribution of reflected photons is negligible in comparison with the classical optical reflectometry scheme. Therefore, the signal-to-noise ratio was increased by at least two orders of magnitude. The obtained experimental data demonstrate the variation of the backflash probability of the single-photon detector depending on the SPAD gate width and the mean photon number per pulse sent by Alice to Bob. Analysis of the calculated backflash probabilities enables to estimate the maximum possible information leakage, depending on the parameters of equipment. In the future, the obtained experimental results can be used to adjust the optimal parameters of QKD systems to guarantee communication protocol security.

Quantum machine Learning (QML) is an emerging technique that leverages quantum theory and the yet-to-be fully developed quantum computers. QML may help solve classification problems that cannot be resolved by deep neural network (DNN). However, QML suffers from a quantum aliasing problem that is created by the inevitable downsampling and binarization operations. QML takes classical data domain as its input, transforms it into a domain of quantum states (a subset of the Hilbert space) using quantum encoding, generates quantum feature vectors, and builds a quantum circuit on the quantum feature vectors—as a machine learning model—to perform classification tasks. Hence, quantum encoding is an important task in QML. However, in addition to the quantum aliasing problem created by the downsampling and binarization operations in the quantum encoding of the classical data to quantum bits, the data scarcity can intensify this problem into an uncontrollable state. This problem has been rarely studied in the QML research literature. Therefore, it is important to study this problem in depth and develop a robust quantum encoding scheme that improves the performance of QML under the influence of data scarcity. In this work, the performance instability of QML under the severity of quantum aliasing and the influence of data scarcity (a combined effect of data and quantum paucity) has been studied by using the TensorFlow Quantum software framework and the MNIST handwritten digits dataset. A quantum encoding—by leveraging Fast Fourier Transform (FFT) and Blackman-Harris window—that encodes the data into qubits to reduce quantum aliasing has been proposed. An empirical study shows that QML significantly improves its learning behavior and performs better than DNN under data scarcity with the use of the proposed FFT-based quantum encoding.

Quantum computing is computationally more powerful than classical one due to the features of superposition and entanglement of quantum bits (qubits). However, because of the non-cloning property, measuring qubits in superposition forces them to collapse onto classical ones, which makes traditional run-time techniques for debugging and analyzing hardware circuits infeasible. To overcome this issue, previous works proposed the concept of quantum dynamic runtime assertion. Stabilizer is an approach adopted for correcting quantum errors. The quantum state can remain unchanged after several Pauli operations. We call these Pauli operations a stabilizer. In this work, we propose to use the quantum stabilizers for dynamic runtime assertions, which requires less quantum gates and increases the detect accuracy on Noisy intermediate scale quantum(NISQ).

Calculations of nuclear properties and nuclear models are performed using quantum computing algorithms on simulated and real quantum computers. The models are a realistic calculation of deuteron binding based on effective field theory, and a simplified two-level version of the nuclear shell model. A method of reducing the number of qubits needed for practical calculation is presented, the reduction being with respect to that used when the standard Jordan-Wigner encoding is used. Its efficacy is shown in the case of the deuteron binding and shell model. A version of the variational quantum eigensolver in which all eigenstates in a spectrum are targeted on an equal basis is shown. The method involves finding the minima of the variance of the Hamiltonian, and its ability to find the full spectrum of small version of the simplified shell model is presented.