Imaging and certifying high-dimensional entanglement with a single-photon avalanche diode camera

Abstract

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 charged coupled device (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 107 frames. Through violation of an Einstein–Podolsky–Rosen criterion by 227 sigmas, we confirm the presence of spatial entanglement between our photon pairs. Furthermore, we certify, in just 140 s, an entanglement dimensionality of 48. Our work demonstrates the potential of SPAD cameras in the rapid characterisation of photonic entanglement, leading the way towards real-time quantum imaging and quantum information processing.

A quantum-enhanced wide-field phase imager

“…𝒱 Classical ( V ) is the interference visibility for classical (N00N) interference, where we set 𝒱 Classical to unity, while we measured 𝒱 = 0.94 ± 0.06. Some photon counting noise is added by the coincidence counting method used here ( 27 , 28 ), which is quantified by κ ≥ 1 (where κ = 1 for ideal shot noise limited measurements). We experimentally measure a value of κ = 1.05 (see SM-S5 for details).…”

“…This is achieved by a half-wave plate (HWP) at 22.5° after SP 2 , and a lateral displacement polarizing beam splitter (dPBS), which directs the photons with diagonal [ D ≡ (H + V ) / √ then measure spatially resolved photon coincidences (18) in the three possible polarization bases, corresponding to 〈DD|〉, 〈AA|〉, and 〈DA|〉 measurements (see Materials and Methods for details). We experimentally characterized and then optimized the SNR of the measured coincidences, which depends on the entangled photon generation rate and camera acquisition parameters (see SM-S5 for details) (27,28). We note that, here, a critical factor is the SPAD array camera's negligible read noise and very high frame rate, enabling the ultralow-noise acquisition of spatially resolved coincidences across 2048 spatial modes defined by the camera's pixels.…”

“…Under low-light conditions, where a pixel receives either zero or one photon, the coincidence counts cc between any two arbitrary pixels i and j can be calculated from N intensity image frames according to (18,27)…”

Spot Tracking and TDC Sharing in SPAD Arrays for TOF LiDAR

“…Circuit complexity can be reduced by employing the so-called time-gated photon-counting mode, in which incoming photons are counted and recorded through digital counters, which are way simpler than TDCs and require a much smaller area, eventually yielding to higher fill-factor arrays [ 20 ]. Figure 1 (right) exemplifies a typical time-gated photon-counting measurement where a gate time-window shifts across the full-scale range and photons are simply counted therein after many laser pulse repetitions, so to finally identify the laser “echo” where the signal photon return is higher.…”

Polarization entanglement-enabled quantum holography

“…on the order of several hours) resulting from the low frame rate of EM-CCD cameras. However, thanks to the rapid development of faster and cheaper sensors for imaging quantum correlations [53,54], we expect quantum holography to move towards practical applications for biological imaging and sensing, but also for characterising complex high-dimensional quantum states, that are likely to be at the heart of tomorrow's quantum optical communications and information processing technologies.…”