Proceedings Volume 8518

Quantum Communications and Quantum Imaging X

cover
Proceedings Volume 8518

Quantum Communications and Quantum Imaging X

View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 5 November 2012
Contents: 8 Sessions, 25 Papers, 0 Presentations
Conference: SPIE Optical Engineering + Applications 2012
Volume Number: 8518

Table of Contents

icon_mobile_dropdown

Table of Contents

All links to SPIE Proceedings will open in the SPIE Digital Library. external link icon
View Session icon_mobile_dropdown
  • Front Matter: Volume 8518
  • Quantum Imaging
  • Quantum Communications I
  • Quantum Communications II
  • Entangelment and Multiphoton Interference
  • Quantum Technology I
  • Quantum Technology II
  • Poster Session
Front Matter: Volume 8518
icon_mobile_dropdown
Front Matter: Volume 8518
This PDF file contains the front matter associated with SPIE Proceedings Volume 8518, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.
Quantum Imaging
icon_mobile_dropdown
Quantum computing based on optical interference: from analogue to digital novel implementations
In a recent experiment, we have shown how optical interference can be exploited in order to perform computations and in particular factoring large integers. This has lead us to the developing of a novel analogue algorithm which allows the factorization of several large integers in a single run. This work represents a step stone towards the developing of novel physical networks able to implement quantum digital algorithms other than Shor’s algorithm. We describe the main ideas leading to this new line of research referring to future publications for a detailed description.
Subwavelength photolithography and microscopy
The resolutions of the optical microscope and the optical lithography are both limited by the well-known Rayleigh limit. Rabi oscillation is a coherent nonlinear process that can modulate the population distribution between two energy states and also modulate the resonant fluorescence spectrum. If we have a gradient electric field amplitude in the space, the Rabi frequency for different position is also different. The spatial distribution of the population in the excited state can be modulated and the spatial information of the atoms can also be encoded in the resonant fluorescence spectrum. If the gradient of the field is large enough, the pattern generated can be subwavlength and the atoms with subwavelength distances can also be extracted. Here we present a review on both the subwavelength photolithography and microscopy via Rabi oscillations.
Ghost imaging experiment with sunlight compared to laboratory experiment with thermal light
Sanjit Karmakar, Ronald Meyers, Yanhua Shih
A recent article reports on the demonstration of ghost imaging using sunlight which also presents theory for ghost imaging in the atmosphere based on two photon interference. The current paper reviews the experiment from a different context than that presented by Karmakar, Meyers and Shih (KMS). Here we examine data from the KMS sunlight ghost imaging experiment and compare it to ghost imaging produced by true thermal light.
Virtual ghost imaging with Bessel beam illumination
We present results from experiments performed at the Army Research Laboratory (ARL) demonstrating a single sensor virtual ghost imaging (VGI) configuration using Bessel beams. These experiments were performed in conditions of partially obscuring media or turbulent media to generate images of remote objects. Randomly translated Bessel beams provided improved illumination capabilities for resolving small distant targets in difficult imaging environments. When the object was illuminated through obscuring or turbulent media or a small offset aperture VGI recovered the image of the object when using a relatively coarse Bessel beam. Our experimental results show that VGI using Bessel beams can have advantages over Gaussian beams for imaging remote objects in adverse conditions.
Quantum Communications I
icon_mobile_dropdown
Incompleteness and limit of security theory of quantum key distribution
Osamu Hirota, Dan Murakami, Kentaro Kato, et al.
It is claimed in the many papers that a trace distance: d guarantees the universal composition security in quantum key distribution (QKD) like BB84 protocol. In this introduction paper, at first, it is explicitly explained what is the main misconception in the claim of the unconditional security for QKD theory. In general terms, the cause of the misunderstanding on the security claim is the Lemma in the paper of Renner. It suggests that the generation of the perfect random key is assured by the probability (1-d), and its failure probability is d. Thus, it concludes that the generated key provides the perfect random key sequence when the protocol is success. So the QKD provides perfect secrecy to the one time pad. This is the reason for the composition claim. However, the quantity of the trace distance (or variational distance) is not the probability for such an event. If d is not small enough, always the generated key sequence is not uniform. Now one needs the reconstruction of the evaluation of the trace distance if one wants to use it. One should first go back to the indistinguishability theory in the computational complexity based, and to clarify the meaning of the value of the variational distance. In addition, the same analysis for the information theoretic case is necessary. The recent serial papers by H.P.Yuen have given the answer on such questions. In this paper, we show more concise description of Yuen's theory, and clarify that the upper bound theories for the trace distance by Tomamichel et al and Hayashi et al are constructed by the wrong reasoning of Renner and it is unsuitable as the security analysis. Finally, we introduce a new macroscopic quantum communication to replace Q-bit QKD.
Photon information efficient communication through atmospheric turbulence
High photon-efficiency (many bits/photon) optical communication is possible with pulse-position modulation and direct detection, and high spectral efficiency (many bits/sec-Hz) optical communication is possible with quadrature-amplitude modulation and coherent detection. These high efficiencies, however, cannot be achieved simultaneously unless multiple spatial modes are employed. Previous work for the vacuum-propagation channel has shown that achieving 10 bits/photon and 5 bits/sec-Hz is impossible with coherent detection, and it requires 189 low diffraction-loss spatial modes at the ultimate Holevo limit, and 4500 such modes at the Shannon limit for on-off keying with direct detection. For terrestrial propagation paths, however, the effects of atmospheric turbulence must be factored into the photon and spectral efficiency assessments. This paper accomplishes that goal by presenting upper and lower bounds on the turbulent channel’s ergodic Holevo capacity for M-mode systems whose transmitters use either focused-beam, Hermite-Gaussian (HG), or Laguerre-Gaussian (LG) modes, and whose receivers do M-mode detection either with or without adaptive optics. The bounds show that use of adaptive optics will not be necessary for achieving high photon efficiency and high spectral efficiency through atmospheric turbulence, although receivers which do not use adaptive optics will need to cope with considerable crosstalk between the spatial patterns produced in their entrance pupils by the M-mode transmitter. The bounds also show the exact theoretical equivalence of the HG and LG mode sets for this application, generalizing a result previously established for the vacuum-propagation channel. Finally, our results show that the FB modes outperform the HG and LG modes in operation with and without adaptive optics.
Quantum channel capacity for OAM based free-space optical communications
We study the channel capacity for orbital angular momentum (OAM) based quantum free-space optical communications. Inspired by recent demonstrations for OAM-based single-photon communication, we construct the quantum density operator in matrix form, based on OAM eigenkets, and determine the quantum channel model suitable for study of the quantum communication over atmospheric turbulence channels. The quantum channel model is derived from OAM eigenkets transition probabilities. By using this model we determine the OAM quantum channel capacity in the presence of atmospheric turbulence. The proposed quantum channel model is of high importance for future study of quantum error correction coding to extend the transmission distance and data rate of free-space quantum communications.
Qudit communication network
Jaewan Kim, Juhui Lee, Sewan Ji, et al.
Optical coherent states can be interpreted as d-dimensional quantum systems, or qudits of even superposition of pseudo-number states. Cross-Kerr nonlinear interaction can generate the maximal entanglements of pseudo- phase and pseudo-number states from two opticl coherent states. Extended network of these entangled coherent states is a qudit cluster state and can be used as qudit communication network for d-dimensional teleportation or multi-user quantum cryptographic network.
Quantum Communications II
icon_mobile_dropdown
Unveiling optical hidden correlations: the illusionist game
Optical correlations represent a resource for the development of technologies with very promising opportunities for future widespread applications.1–14 Here we will show, both theoretically and experimentally, the optical illusionist game, an innovative protocol that exploit correlations between thermal beams of light.15 In the game, an illusionist demonstrates that if two uncorrelated light beams excited in the same state are mixed in a beam splitter (BS), then no correlations arise between them. On the other hand, the presence of the BS can be identified by the illusionist when the public is asked to insert the BS behind the illusionist’s back. Here we unveil the trick and the physics that explain these counterintuitive correlations. 1
Air to ground quantum key distribution
Sebastian Nauerth, Florian Moll, Markus Rau, et al.
To enable global scale quantum key distribution1-3 (QKD), satellite based systems 4,5 are the most promising approach. So far, free-space QKD has already been demonstrated on communication channels with attenuation comparable to satellite downlinks,6 and classical laser communications with satellites and aircrafts is heavily explored.7-10 Here, combining both these challenges, we demonstrate an aircraft to ground QKD transmission obtaining a sifted key rate of 145 bit/s and a QBER, larglely dominated by background events and stray light, of 4:8 %.
A quantum network with atoms and photons (QNET-AP)
Ronald E. Meyers, Patricia Lee, Keith S. Deacon, et al.
Enabling secure communication, unparalleled computing capabilities, and fundamental nonlocality physics exploration, the development of quantum repeaters is the key quantum information processing technology advance needed for implementing real world quantum networks beyond the laboratory environment. Currently, components exist for intra-laboratory quantum networks but no system exists for connecting distant ( 1 km ) quantum memories in the real world. We present a physics analysis of quantum repeater network designs for intracity optical fiber connections between nodes based on atomic memories and linear optics. Long distances will necessitate the use of (1) two-photon Hong-Ou-Mandel style interference between atomic ensembles for entanglement swapping, and (2) photonic qubit wavelength conversion between atomic emissions and photons at telecommunication wavelengths in fiber. We report on our experimental progress towards implementing A Quantum Network with Atoms and Photons (QNET-AP), a quantum repeater network test-bed, between the US Army Research Laboratory (ARL) and the Joint Quantum Institute (JQI) of the National Institute of Standards and Technology (NIST) and the University of Maryland (UMD).
Entangelment and Multiphoton Interference
icon_mobile_dropdown
Two-particle quantum transmission
Ron Folman
Two-photon interference is a fundamental phenomenon in quantum mechanics and stands at the base of numerous experimental observations. Here another manifestation of this phenomenon is described, taking place at a Y junction. Specifically it is shown how the r2 + t2 term which is behind previous observations of two-photon interference, may give rise to different states at a beam- splitter and different two-particle transmission coefficients at a Y junction. Different from previous descriptions of quantum transmission based on one-particle physics, the enhanced transmission described here is due to two-particle physics.
Generation of spatially pure photon pairs in a multimode nonlinear waveguide using intermodal dispersion
Michal Karpinski, Czeslaw Radzewicz, Konrad Banaszek
We present experimental realization of type-II spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate (KTiOPO4) nonlinear waveguide. We demonstrate that by careful exploitation of intermodal dispersion in the waveguide it is feasible to produce photon pairs in well defined transverse modes without any additional spatial filtering at the output. Spatial characteristics is verified by measurements of the M2 beam quality factors. We also prepared a postselected polarization-entangled two-photon state shown to violate Bell’s inequality. Similar techniques based on intermodal dispersion can be used to generate spatial entanglement and hyperentanglement.
Quantum Technology I
icon_mobile_dropdown
Experimental investigation of the X-shaped spatio-temporal correlation of twin photons via sum frequency generation
Ottavia Jedrkiewicz, Enrico Brambilla, Paolo Di Trapani, et al.
In this paper we report about the experimental investigation of the non factorable spatio-temporal correlation of twin beams generated in parametric down conversion (PDC) at the crystal output. We present the correlation features to be reconstructed by means of the inverse process of PDC, that is sum frequency generation, in a scheme based on achromatic imaging. In particular we show the ultra-narrow temporal localization (6fs) observed thanks to the huge spectral bandwidth detected in the near field of the crystal. We illustrate the deteriorating effects of imperfect imaging conditions or spatial modes selection on the temporal correlation, giving evidence of the interdependence of spatial and temporal degrees of freedom in PDC as claimed by the theory. Throughout the paper we shall discuss about the characteristics of the experimental set-up being used for the investigation of the twin beam correlation in both the temporal and spatial domain, highlighting the important features for the success of the experiment and the demonstration of the X-shaped structure of the space-time correlation, already emerging from preliminary results.
Experimental realization of an approximate partial transpose for photonic two-qubit systems
Hyang-Tag Lim, Yong-Su Kim, Young-Sik Ra, et al.
The partial transpose by which a subsystem's quantum state is solely transposed is of unique importance in quantum information processing from both fundamental and practical point of view. In this work, we present a practical scheme to realize a physical approximation to the partial transpose using local measurements on individual quantum systems and classical communication. We then report its linear optical realization and show that the scheme works with no dependence on local basis of given quantum states. A proof-of-principle demonstration of entanglement detection using the physical approximation of the partial transpose is also reported.
Quantum limits of super-resolution via sparsity constraint
Sparsity constraint is a priori knowledge of the signal, which means that in some properly chosen basis only a small percentage of the signal components is nonzero. Sparsity constraint has been used in signal and image processing for a long time. Recent publications have shown that by taking advantage of the Sparsity constraint of the object, super-resolution beyond the diffraction limit could be realized. In this paper we present the quantum limits of super-resolution for the sparse objects. The key idea of our paper is to use the discrete prolate spheroidal sequences (DPSS) as the sensing basis. We demonstrate both analytically and numerically that this sensing basis gives superior performance over the Fourier basis conventionally used for sensing of sparse signals. The explanation of this phenomenon is in the fact that the DPSS are the eigenfunctions of the optical imaging system while the Fourier basis are not. We investigate the role of the quantum fluctuations of the light illuminating the object, in the performance of reconstruction algorithm. This analysis allows us to formulate the criteria for stable reconstruction of sparse objects with super-resolution.
Quantum Technology II
icon_mobile_dropdown
680-890nm spectral range of nickel-nitrogen and nickel-silicon complex single centres in diamond
Stefania Castelletto, Andrew Edmonds
Fluorescent emitters in nanodiamonds are considered to be a valuable resource for emerging fields such as quantum communication, quantum photonics and biological imaging. In this paper we report a wide range of narrow bandwidth spectral emission lines arising from different color centers at room temperature. We associate the zero phonon lines, observed using confocal microscopy, with previously identified nickel-related centers in high pressure high temperature diamond, with a Si/Ni complex and silicon vacancy defects. In particular we show the first observation of a 850 nm emission in diamond with single photon signature, indicating the potential for diamond to harbor infrared single-photon sources. Index Terms diamond defects, single-photon emission, confocal microscopy.
Bounds on parameter estimation precision for optical ranging systems
Many errors contribute to the accuracy of a ranging system, among them calibration and estimation errors. In this paper we address the estimation error contribution of an optical ranging system. We present achievable RMS errors in estimating the phase, frequency, and intensity of a direct-detected intensity-modulated optical pulse train. For each parameter, the Cramèr-Rao-Bound (CRB) is derived and the performance of the Maximum Likelihood estimator is illustrated. Approximations to the CRBs are provided, enabling an intuitive understanding of estimator behavior as a function of the signaling parameters. The results are compared to achievable RMS errors in estimating the same parameters from a sinusoidal waveform in additive white Gaussian noise. This establishes a framework for a performance comparison of radio frequency (RF) and optical science. Comparisons are made using parameters for state-of-the-art deep-space RF and optical links. Degradations to the achievable errors due to clock phase noise and detector jitter are illustrated.
Dual-channel, single-photon upconversion detector near 1300 nm
Paulina S. Kuo, Jason S. Pelc, Oliver Slattery, et al.
Upconversion of 1.3-micron photons and detection using silicon avalanche photodiodes (Si APDs) can produce high photon detection efficiencies (PDEs) with low dark count rates. We demonstrate a novel two-channel device based on a phase-modulated, periodically poled LiNbO3 waveguide that mixes 1302-nm signal photons with two pump beams at 1556 and 1571 nm. Both channels showed high PDEs with very low dark counts. Using wavelength- to time-division multiplexing in this dual-channel device, we produced clock rates that exceed the timing-jitter-limited rates of a system based on one Si APD. Higher clock rates are of interest for improved quantum communication systems.
Poster Session
icon_mobile_dropdown
Positive-negative turbulence-free ghost imaging experiments
Experiments were performed at the Army Research Laboratory (ARL) that observed turbulence-free positive and negative thermal light ghost images from independently recorded event histories of a “bucket” photo-detector and a charged coupled device (CCD) array. The positive (negative) ghost images were computed from the “bucket” detector counts which were above (below) their means, and the ghost images were not degraded by the turbulence. This paper provides a quantum interference model which effectively explains how the “bucket” photon counts yield positive or negative ghost images with a distant CCD array.
SPDC correlated photon source filtered for narrowed bandwidth using volume Bragg grating
Oliver Slattery, Paulina Kuo, Yong-Su Kim, et al.
A Volume Bragg Grating (VBG) can be used to efficiently extract a narrow bandwidth, highly collimated beam from an otherwise broad spectrum beam. We use a VBG to extract a narrow bandwidth of signal spectrum from a broadband Spontaneous Parametric Down-Conversion source to optimally match the narrow detection bandwidth of our idler upconversion detector. Improved coincidence count rates and visibility can be achieved when limiting signal-spectrum detection to the narrow signal bandwidth whose photons are correlated with a narrow idler-spectrum bandwidth that has been selected by the up-conversion detector. We compare coincidence count rate and visibility for when the entire signal spectrum is detected and when the spectrum has been filtered by the VBG. We further relax the collection techniques and show that following the VBG, the coincidence count rate improves with minimal loss in visibility compared to when the entire spectrum is detected. We introduce our initial efforts at using the VBG to further narrow the signal spectrum by placing it inside a multipass cavity. Additionally, we further adapt the single photon level up-conversion spectrometer, previously developed for idler spectrum measurement, to indirectly measure the single photon level signal spectrum. We verify its capability for several different wavelength and linewidth selections.
Quantum processing through a manifold of dark states
Santosh Kumar, Deepak Kumar
We propose a scalable network, in which all quantum operations can be executed through external controls. Nodes of this network are high-finesse electromagnetic cavities, each coupled to a single three-level atom. The nodes are connected by optical fibers. Each atom is addressed by a control laser, which along with the cavity field drives atomic transitions. The network can be in the form of arrays of N-cavities connected by NB fibers in one to three dimensions. We find that under certain conditions, the system possesses two kinds of degenerate dark states. The first kind are N states corresponding to atomic excitations at each node and these are our logical states for quantum processing. The second kind are NB states on pairs of sites connected by a fibre. By manipulating intensities and phases of control lasers on the cavities, one can pass adiabatically among these dark states due to their degeneracy. This network operates as a N-level quantum system in which one can generate computationally useful states by protocols of external controls. We obtain numerical results for small chains and square lattices to demonstrate some quantum operations like the transport of states across the array, generation of superposed states and phase-flipping in a network. We also discuss effects of dissipation and limitations of the model.
Engineering of spectral properties of two-photon states, preliminary results
Alessio Avella, Giorgio Brida, Maria Chekhova, et al.
We present an experimental implementation of spectral properties engineering on biphoton light, emitted via ultrafast type II spontaneous parametric down conversion (SPDC), based on the shaping of the pump pulse spectrum and propagation of the emitted correlated photons through dispersive media. Spectral properties of a biphoton state are fully characterized by the two-photon spectral amplitude (TPSA). Exploiting the group velocity dispersion (GVD) induced by the passage of optical fields through dispersive media, an energy to time two dimensional Fourier transform of the TPSA is operated: this returns a technique to reconstruct TPSA by means of a temporal measurement among the delay between the laser pulse emission (trigger) and the detection times of the two correlated photons. Exploiting this kind of measurement it is possible to deeply resolve the interference pattern in the shape of TPSA. In this research we report on the conditions under which subtle structure on TPSA spectra can be deliberately engineered via modulation of the pump beam spectrum.
Capacity approaching codes for photon counting receivers
Marina Mondin, Fred Daneshgaran, Inam Bari, et al.
[1] a low-complexity photon-counting receiver has been presented, which may be employed for weak-energy optical communications and which is typically modeled through its equivalent Binary Symmetric Channel (BSC) model. In this paper we consider the scheme described in [1], we model it as a time varying Binary Input-Multiple Output (BIMO) channel and analyze its performance in presence of soft-metric based capacity approaching iteratively decoded error correcting codes, and in particular using soft-metric based Low Density Parity Check (LDPC) codes. To take full advantage of such detector, soft information is generated in the form of Log-Likelihood Ratios (LLRs), achieving reduction in Bit Error Rate (BER) and Frame Error Rate (FER) with respect to classical BSC and Additive White Gaussian Noise (AWGN) channel models. Furthermore, we explore the limits of the achievable performance gains when using photon counting detectors as compared to the case when such detectors are not available. To this end, we find the classical capacity of the considered BIMO channel, clearly showing the potential gains that photon counting detectors can provide in the context of a realistic cost-effective scheme from an implementation point of view. Furthermore, we show that from a channel modeling point of view, we can observe that the BIMO channel can be approximated with an AWGN channel for high values of mean photon count Nc, while the AWGN model offers an unreliable result with a low mean photon number Nc, (i.e. with low raw BER). This effect is more evident with lower coding rates.