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.
Highlights
Individual single-photon avalanche diodes (SPADs) have long been the workhorse of many quantum optics experiments[1,2]
singlephoton avalanche diode (SPAD) cameras have yet to make their mark due to their overall efficiency and resolution; the fill factor of the earliest available SPAD cameras was on the order of a few percent[6,18], which, despite the quantum efficiency of the single SPAD pixels being on par with commercial single element SPADs, equates to a large overall loss
This, in turn, is a result of the photon source of choice that is usually spontaneous parametric down-conversion (SPDC) in non-linear crystals, where a pump photon is converted with a given probability, into a pair photons
Summary
Individual single-photon avalanche diodes (SPADs) have long been the workhorse of many quantum optics experiments[1,2]. Precise timing electronics results in an impulse response function that can be as short as 20 ps[3], which is ideal for measuring temporal correlations between multiple photons while reducing the influence of background radiation and dark counts These properties make SPADs one of the leading technologies for measuring photon–photon correlations and entanglement. SPAD cameras have yet to make their mark due to their overall efficiency and resolution; the fill factor of the earliest available SPAD cameras was on the order of a few percent[6,18], which, despite the quantum efficiency of the single SPAD pixels being on par with commercial single element SPADs, equates to a large overall loss This high loss is detrimental to the detection of quantum states formed of multiple photons as it scales with the power of the photon number. Ianzano et al.[30] have demonstrated the measurement of polarisation entanglement using a camera, owing to its high-temporal resolution (1.5 ns)
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