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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Quantum correlations in position, momentum and intermediate bases, measured using fiber arrays

Frauke Izdebski, Jonathan Leach, Ryan E. Warburton, David G. Ireland, Stephen Mark Barnett, Alison M. Yao, Gerald S. Buller, Miles J. Padgett

Published Jan 10, 2012• 1 citation
Publisher

Abstract

We have developed a new approach to measuring the spatial position of a single photon. Using fibers of different length, all connected to a single detector allows us to use the high timing precision of single photon avalanche diodes (SPAD) to spatially locate the photon. We have built two 8-element detector arrays to measure the full-field quantum correlations in position, momentum and intermediate bases for photon pairs produced in parametric down conversion. The strength of the position-momentum correlations is found to be an order of magnitude below the classical limit.

DOI
10.1117/12.912055

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We have developed a new approach to measuring the spatial position of a single photon. Using fibers of different length, all connected to a single detector allows us to use the high timing precision of single photon avalanche diodes (SPAD) to spatially locate the photon. We have built two 8-element detector arrays to measure the full-field quantum correlations in position, momentum and intermediate bases for photon pairs produced in parametric down conversion. The strength of the position-momentum correlations is found to be an order of magnitude below the classical limit.
We report an eight-element, linear-array, single-photon detector that uses multiple fibers of differing lengths coupled to a single detector, the timing information from which reveals the position in which the photon was measured. Using two such arrays and two detectors we measure the correlations of photons produced by parametric downconversion, without recourse to mechanical scanning. Spatial light modulators acting as variable focal length lenses positioned between the downconversion crystal and the arrays allow us to switch between measurement of position, transverse momentum, or intermediate bases. We observe the product of the variances of the conditional probabilities for position and momentum to be more than an order of magnitude below the classical limit, realizing a full-field demonstration of the Einstein-Podolsky-Rosen paradox. Such, multistate measurement technologies allow access to the higher information content of the photon based upon spatial modes.
use of any of the information contained in it must acknowledge this thesis as the source of the quotation or information. This thesis investigates the measurement of spatial correlations of photon pairs gener-ated through spontaneous parametric down-conversion with single-photon sensitive multi-pixel detectors. A custom designed and fabricated 8×1 fibre array detector for time to position multi-plexing was characterised. This detector was then commissioned in an experiment measuring the spatial correlations of photon pairs in position, momentum and in-termediate bases. The fibre array measured eight positions simultaneously with one Single-Photon Avalanche Diode, which led to an eight-fold increase in the data ac-quisition rate compared to traditional experiments, where a single SPAD was scanned across the detection plane. To capture all of the emitted light, an electron-multiplying CCD (EMCCD) camera was used. The spatial correlations were measured for the first time in momentum and pos-
Spatial correlations between two photons are the key resource in realising many quantum imaging schemes. Measurement of the bi-photon correlation map is typically performed using single-point scanning detectors or single-photon cameras based on CCD technology. However, both approaches are limited in speed due to the slow scanning and the low frame-rate of CCD-based cameras, resulting in data acquisition times on the order of many hours. Here we employ a high frame rate, single photon avalanche diode (SPAD) camera, to measure the spatial joint probability distribution of a bi-photon state produced by spontaneous parametric down-conversion, with statistics taken over 10710^7107 frames acquired in just 140 seconds. We verified the presence of spatial entanglement between our photon pairs through the violation of an Einstein-Podolsky-Rosen criterion, with a confidence level of 227 sigmas. Our work demonstrates the potential of SPAD cameras in the rapid characterisation of photon correlations, leading the way towards quantum imaging in real-time.
Single-photon avalanche diode (SPAD) arrays are essential tools in biophotonics, optical ranging and sensing, and quantum optics. However, their small number of pixels, low quantum efficiency, and small fill factor have so far hindered their use for practical imaging applications. Here, we demonstrate full-field entangled photon-pair correlation imaging using a 100-kpixel SPAD camera. By measuring photon coincidences between more than 500 million pairs of positions, we retrieve the full point spread function of the imaging system and subsequently high-resolution images of target objects illuminated by spatially entangled photon pairs. We show that our imaging approach is robust against stray light, enabling quantum imaging technologies to move beyond laboratory experiments towards real-world applications such as quantum light detection and ranging.
Single-photon avalanche diode arrays can provide both the spatial and temporal information of each detected photon. We present here the characterization of spatially entangled photons with a 32 × 32 pixel sensor, specifically designed for quantum imaging applications. The sensor is time-tagging each detection event at pixel level with sub-nanosecond accuracy within frames of 50 ns. The spatial correlations between any number of detections in a defined temporal window can thus be directly extracted from the data.The space-momentum entanglement of photon pairs is demonstrated by violating an EPR-type inequality directly from the measured near-field correlations and far-field anti-correlations.
Abstract We demonstrate an experimental scheme for high-precision position measurements based on transverse-momentum-resolved two-photon interferometry with independent photons and single photon avalanche diode (SPAD) arrays. Our scheme extends the operative range of Hong–Ou–Mandel interferometry beyond its intrinsic constraints due to photons indistinguishability, paving the way to applications in high-resolution imaging. We assess the experimental results against the ultimate precision bounds as determined by quantum estimation theory. Our experiment ultimately proves that transverse-momentum resolved measurements of fourth-order correlations in the fields can be employed to overcome spatial distinguishability between independent photons. The relevance of our results extends beyond sensing and imaging towards quantum information processing, as we show that partial photon distinguishability and entanglement impurity are not necessarily a nuisance in a technique that relies on two-photon interference.