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arXiv:2101.03120 · Optics Letters

Fast imaging of multimode transverse–spectral correlations for twin photons

Michał Lipka, Michal P. Parniak

Published May 26, 2021• 7 citations
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Abstract

Hyperentangled photonic states-exhibiting nonclassical correlations in several degrees of freedom-offer improved performance of quantum optical communication and computation schemes. Experimentally, a hyperentanglement of transverse-wave-vector and spectral modes can be obtained in a straightforward way with multimode parametric single-photon sources. Nevertheless, experimental characterization of such states remains challenging. Not only single-photon detection with high spatial resolution-a single-photon camera-is required, but also a suitable mode converter to observe the spectral-temporal degree of freedom. We experimentally demonstrate a measurement of full four-dimensional transverse-wave-vector-spectral correlations between pairs of photons produced in noncollinear spontaneous parametric downconversion. Utilization of a custom ultrafast single-photon camera provides high resolution and a short measurement time.

DOI
10.1364/ol.417658

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Hyperentangled photonic states-exhibiting nonclassical correlations in several degrees of freedom-offer improved performance of quantum optical communication and computation schemes. Experimentally, a hyperentanglement of transverse-wave-vector and spectral modes can be obtained in a straightforward way with multimode parametric single-photon sources. Nevertheless, experimental characterization of such states remains challenging. Not only single-photon detection with high spatial resolution-a single-photon camera-is required, but also a suitable mode converter to observe the spectral-temporal degree of freedom. We experimentally demonstrate a measurement of full four-dimensional transverse-wave-vector-spectral correlations between pairs of photons produced in noncollinear spontaneous parametric downconversion. Utilization of a custom ultrafast single-photon camera provides high resolution and a short measurement time.
We experimentally demonstrate the first quantum system entangled in every degree of freedom (hyperentangled). Using pairs of photons produced in spontaneous parametric down-conversion, we verify entanglement by observing a Bell-type inequality violation in each degree of freedom: polarization, spatial mode, and time energy. We also produce and characterize maximally hyperentangled states and novel states simultaneously exhibiting both quantum and classical correlations. Finally, we report the tomography of a 2 x 2 x 3 x 3 system (36-dimensional Hilbert space), which we believe is the first reported photonic entangled system of this size to be so characterized.
The Hong-Ou-Mandel interference effect lies at the heart of many emerging quantum technologies whose performance can be significantly enhanced with increasing numbers of entangled modes one could measure and thus utilize. Photon pairs generated through the process of spontaneous parametric down conversion are known to be entangled in a vast number of modes in the various degrees of freedom (DOF) the photons possess such as time, energy, and momentum, etc. Due to limitations in detection technology and techniques, often only one such DOFs can be effectively measured at a time, resulting in much lost potential. Here, we experimentally demonstrate, with the aid of a time tagging camera, high speed measurement and characterization of two-photon interference. With a data acquisition time of only a few seconds, we observe a bi-photon interference and coalescence visibility of ∼64% with potentially up to ∼2 × 103 spatial modes. These results open up a route for practical applications of using the high dimensionality of spatiotemporal DOF in two-photon interference, and in particular, for quantum sensing and communication.
High-dimensional encoding in time-frequency and photon-number degrees of freedom promises photon-efficient quantum communication, but requires detectors that are both temporal-mode selective and photon-number resolving. Here we demonstrate time-correlated single-photon detection combining both capabilities. A train of shaped pump pulses drives quantum frequency up-conversion to select a chosen temporal mode, and the converted photons are counted with a photon-number-resolving detector. Applying to a photon-pair source by spontaneous parametric downconversion into signal and idler bands, we demonstrate direct sampling of the high-dimensional correlated quantum states on compound time-frequency and photon number bases. Our measurements show that the up-converted photons in each band exhibit thermal photon-number statistics, indicating strong single-mode selection. We reconstruct joint temporal intensities conditioned on one and two photon pairs, revealing signal-idler correlations in both time-frequency and photon number. Together, these results establish a unified technology framework linking high-dimensional quantum correlations, mode-selective photon measurement, and photon-number resolved detection. This approach provides a route to characterizing multimode photon-pair sources and to larger time-frequency and photon-number alphabets for high-dimensional quantum communication and information processing.
High-dimensional encoding in time-frequency and photon-number degrees of freedom promises photon-efficient quantum communication, but requires detectors that are both temporal-mode selective and photon-number resolving. Here we demonstrate time-correlated single-photon detection combining both capabilities. A train of shaped pump pulses drives quantum frequency up-conversion to select a chosen temporal mode, and the converted photons are counted with a photon-number-resolving detector. Applying to a photon-pair source by spontaneous parametric downconversion into signal and idler bands, we demonstrate direct sampling of the high-dimensional correlated quantum states on compound time-frequency and photon number bases. Our measurements show that the up-converted photons in each band exhibit thermal photon-number statistics, indicating strong single-mode selection. We reconstruct joint temporal intensities conditioned on one and two photon pairs, revealing signal-idler correlations in both time-frequency and photon number. Together, these results establish a unified technology framework linking high-dimensional quantum correlations, mode-selective photon measurement, and photon-number resolved detection. This approach provides a route to characterizing multimode photon-pair sources and to larger time-frequency and photon-number alphabets for high-dimensional quantum communication and information processing.
Parametric down-conversion converts pump photons in pairs of correlated signal and idler photons. Even when pumped by a single-mode laser, the signal and idler photons are spread over several thousand spatial modes yet strongly correlated with each other in their position and transverse momentum. These correlations enable applications in imaging, sensing, communication, and optical processing. Here we show that, using a photon number resolving camera, spatial correlations can be observed after only a few 10s seconds measurement time. Photon number resolving camera technologies are likely to find wide use in quantum enhanced low-light imaging systems.