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SPIE Quantum Technologies

Taking photos of quantum entanglement

Baptiste Courme, Chloé Vernière, Patrick Cameron, Raj Pandya, Hugo Defienne

Published Jun 10, 2024• 0 citations
Publisher

Abstract

Entanglement is a central resource in quantum technologies. In this respect, high-dimensional entangled states are very promising for developing robust quantum communication schemes and enhanced imaging protocols. Being able to quantify high-dimensional entanglement quickly and accurately is therefore essential. However, to date, all experimental methods use assumptions about the detected state or imperfect measurement techniques, such as single-outcomes and accidental subtractions. Entanglement certification processes are therefore not only slow, but they also contain loopholes, which is not acceptable in adversarial scenarios such as quantum key distribution (QKD). In our work, we demonstrate the certification of high-dimensional entanglement using an event-based single-photon sensitive camera by performing measurements in two mutually unbiased bases. Our work provides an experimental method allowing for the efficient characterization of high-dimensional quantum states, paving the way for the development of high-dimensional QKD protocols and practical photon-pairs-based quantum imaging approaches.

DOI
10.1117/12.3022601

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Entanglement is a central resource in quantum technologies. In this respect, high-dimensional entangled states are very promising for developing robust quantum communication schemes and enhanced imaging protocols. Being able to quantify high-dimensional entanglement quickly and accurately is therefore essential. However, to date, all experimental methods use assumptions about the detected state or imperfect measurement techniques, such as single-outcomes and accidental subtractions. Entanglement certification processes are therefore not only slow, but they also contain loopholes, which is not acceptable in adversarial scenarios such as quantum key distribution (QKD). In our work, we demonstrate the certification of high-dimensional entanglement using an event-based single-photon sensitive camera by performing measurements in two mutually unbiased bases. Our work provides an experimental method allowing for the efficient characterization of high-dimensional quantum states, paving the way for the development of high-dimensional QKD protocols and practical photon-pairs-based quantum imaging approaches.
High-dimensional entanglement is a promising resource for quantum technologies. Being able to certify it for any quantum state is essential. However, to date, experimental entanglement certification methods are imperfect and leave some loopholes open. Using a single-photon-sensitive time-stamping camera, we quantify high-dimensional spatial entanglement by collecting all output modes and without background subtraction, two critical steps on the route toward assumptions-free entanglement certification. We show position-momentum Einstein-Podolsky-Rosen (EPR) correlations and quantify the entanglement of formation of our source to be larger than 2.8 along both transverse spatial axes, indicating a dimension higher than 14. Our work overcomes important challenges in photonic entanglement quantification and paves the way toward the development of practical quantum information processing protocols based on high-dimensional entanglement.
High-dimensional entanglement is a promising resource for quantum technologies [1], [2]. Being able to certify it for any quantum state is essential. However, to date, experimental entanglement certification methods are imperfect and leave some loopholes open, due to the presence of accidental coincidences and the hypotheses necessary for their subtraction in post-processing [3], [4]. We present here an experimental study of the role of these accidentals depending on the temporal resolution of the coincidence detection apparatus. Our results show that high-dimensional entanglement certification can be achieved without accidental subtraction using current single-photon camera technologies. Using the recently developed time-stamping Tpx3Cam camera [5], we certify high-dimensional entanglement without accidental subtraction in under 16 seconds. In our experiment, we measure position-momentum Einstein-Podolsky-Rosen (EPR) [6] correlations in pairs of photons generated by Spontaneous Parametric Down Conversion (SPDC) by collecting all spatial output modes simultaneously on the camera. We achieved an EPR factor of0.13<1/20.13 < 1/20.13<1/2, which allows us to certify entanglement.
We derive a framework for quantifying entanglement in multipartite and high dimensional systems using only correlations in two mutually unbiased bases. We furthermore develop such bounds in cases where the second basis is not characterized, thus enabling entanglement quantification with minimal assumptions. To demonstrate the experimental feasibility of the approach we develop an experimental proposal with state of the art cameras and optical lenses and show that these methods enable a reliable characterization of sources of entangled photons with minimal effort.
High-dimensional entangled states, such as spatially-entangled photon pairs produced by Spontaneous Parametric Down-Conversion (SPDC), are a key resource for quantum technologies. In recent years, camera-based coincidence counting approaches have considerably improved the ability to characterize them in terms of speed and dimensionality. However, these methods have limitations, including in most of them the necessity to subtract accidental coincidences. Here, we study the role of these accidentals in entanglement certification for a single-photon avalanche diode (SPAD) array and an intensified time-stamping (Tpx3Cam) camera. Using both Einstein-Podolsky-Rosen (EPR) and entropy-based criteria, we show that the level of accidental coincidences - determined by the temporal characteristics of the camera - and whether they are subtracted critically impact entanglement certification. In particular, we demonstrate that current single-photon camera technologies enable entanglement certification without accidental subtraction only if a Gaussian approximation is applied to the measured two-photon state. Our work is important for developing quantum-optics application in adversarial scenarios, such as high-dimensional quantum key distribution (HD-QKD), and also for loophole-free experimental testing of quantum foundations.
High-dimensional entangled states, such as spatially entangled photon pairs produced by spontaneous parametric down-conversion (SPDC), are a key resource for quantum technologies. In recent years, camera-based coincidence counting approaches have considerably improved the ability to characterize them in terms of speed and dimensionality. However, these methods have limitations, including in most of them the necessity to subtract accidental coincidences. Here, we study the role of these accidentals in entanglement certification for a single-photon avalanche diode (SPAD) array and an intensified time-stamping (Tpx3Cam) camera. Using both Einstein-Podolsky-Rosen (EPR) and entropy-based criteria, we show that the level of accidental coincidences-determined by the temporal characteristics of the camera-and whether they are subtracted critically impact entanglement certification. In particular, we demonstrate that current single-photon camera technologies enable entanglement certification without accidental subtraction only if a Gaussian approximation is applied to the measured two-photon state. Our work is important for developing quantum-optics applications in adversarial scenarios, such as high-dimensional quantum key distribution (HD-QKD) and also for loophole-free experimental testing of quantum foundations.
Certifying entanglement is an important step in the development of many quantum technologies, especially for higher-dimensional systems, where entanglement promises increased capabilities for quantum communication and computation. A key feature distinguishing entanglement from classical correlations is the occurrence of correlations for complementary measurement bases. In particular, mutually unbiased bases (MUBs) are a paradigmatic example that is well-understood and routinely employed for entanglement certification. However, implementing unbiased measurements exactly is challenging and not generically possible for all physical platforms. Here, we extend the entanglement-certification toolbox from correlations in MUBs to arbitrary bases. This practically significant simplification paves the way for efficient characterizations of high-dimensional entanglement in a wide range of physical systems. Furthermore, we introduce a simple three-MUBs construction for all dimensions without using the Wootters-Fields construction, potentially simplifying experimental requirements when measurements in more than two MUBs are needed, especially in high-dimensional settings.