Classical and linear measurements are bound by the shot noise limit. In optics, the sensitivity increases i) with the square root of the number of photons detected, or ii) with the photons-sample interactions. Case (i) is limited by how safe or efficient is the power level, while (ii) is limited by how to achieve and resolve any number of interactions. We report a versatile interference contrast imaging technique, which extracts more information per photon resource than any linear phase imager to date. It is based on a non-resonant multipass design that allows to efficiently implement case (ii) and extract holographic information by using a single photon camera. It has been designed as a wide-field imaging (i.e., without requiring pixel-scanning) technique, able to image highly transparent/reflective samples, with noise reduction beyond 0.22 in less than 7 rounds.
Polarization-Entangled Photon Sources (EPS) are an important enabling technology in the fields of quantum sensing, quantum communication, and quantum computing. Recently, a need has arisen for efficient sources of entangled photons with high brightness and phase stability, for use in free space and fiber-based quantum communication links. In this work, we present a prototype of EPS based on commercial bulk opto-mechanical components, generating photon pairs via type-0 parametric down-conversion (SPDC). The source is configured in a linear interferometer, where a dual beam displacement is performed by symmetrically disposed birefringent components. The pairs emission can be prepared as an N00N state for quantum sensing, or as a Bell state for entanglement-based Quantum Key Distribution (QKD) protocols. We show a maximal Bell inequality violation, on ⪆99% average visibility, proving the high quality of the generated entanglement. The unique geometry of this interferometer is intrinsically symmetric, thus completely removing any temporal walk-off and decoherence between the two components of the Bell state and enhancing its suitability for various on-field quantum applications.
Quantum technology promises improvements in imaging, computing, and communication, for example using the resource of entanglement between photons with spatial correlations. Detecting spatial correlations, or coincidences, between entangled photons scalably, efficiently, and affordably is therefore an essential capability. However, this task is non-trivial for existing camera technologies, which require low illumination intensities or low detection duty cycles to count coincidences at high signal-to-noise ratios, resulting in long acquisition time, or use expensive custom electronic components. Here, we present an entanglement imaging system based around a novel Single-Photon Avalanche Diode (SPAD) array camera, optimized for sparse illumination with correlated photon pairs. The system is capable of maintaining a duty cycle close to 100%, while simultaneously detecting spatially resolved coincidences with high SNR, enabling the acquisition of real-time entanglement videos at a ~Hz frame rate. We use our system to demonstrate real-time monitoring of entanglement interference visibility, optical system point spread function, as well as real-time widefield entanglement-enhanced phase imaging. Our results show that SPAD array cameras represent a natural choice for scalable entanglement detection and imaging applications.
In this work we do a brief analysis of some widespread technologies for imaging science and security, while we also propose new techniques to exceed their standard classical limits by using quantum illumination and quantum detection, and exploiting special quantum modulation phenomena.
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