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Optica Quantum

High-performance source of indistinguishable polarization-entangled photons with a local oscillator reference for quantum networking

Michael B. Grayson, Shawn Meyer, Daniel Sörensen, Abigail Gookin, Markus Allgaier, Nicholas V. Nardelli, Tara M. Fortier, Dileep V. Reddy, T. R. Schibli, Martin J. Stevens, Juliet T. Gopinath, Juliet T. Gopinath, Lynden K. Shalm

Published Aug 20, 2026• 1 citation
Publisher

Abstract

Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact source of indistinguishable pairs of polarization-entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves (99.11±0.01)% polarization entanglement visibility, (96.3±0.6)% successive-photon Hong–Ou–Mandel interference visibility, (68.0±0.1)% heralded efficiency as detected, and (88.6±0.2)% interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.

DOI
10.1364/opticaq.601916

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Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact source of indistinguishable pairs of polarization-entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves (99.11±0.01)% polarization entanglement visibility, (96.3±0.6)% successive-photon Hong–Ou–Mandel interference visibility, (68.0±0.1)% heralded efficiency as detected, and (88.6±0.2)% interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.
Optical quantum networking protocols impose stringent requirements on the states produced by sources of entanglement. We demonstrate a free-space, compact, source of indistinguishable pairs of polarization entangled photons, with an integrated local oscillator reference as a significant step towards this goal. This source achieves (99.11±0.01)%(99.11 \pm 0.01) \%(99.11±0.01)% polarization entanglement visibility, (96.3±0.6)%(96.3 \pm 0.6) \%(96.3±0.6)% successive-photon Hong-Ou-Mandel interference visibility, (68.0±0.1(68.0 \pm 0.1(68.0±0.1) \% heralded efficiency as detected, and (88.6±0.2)%(88.6 \pm 0.2) \%(88.6±0.2)% interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.
Sources of entanglement are an enabling resource in quantum technology, and pushing the limits of generation rate and quality of entanglement is a necessary prerequisite towards practical applications. Here, we present an ultrabright source of polarization-entangled photon pairs based on time-reversed Hong-Ou-Mandel interference. By superimposing four pair-creation possibilities on a polarization beam splitter, pairs of identical photons are separated into two spatial modes without the usual requirement for wavelength distinguishability or noncollinear emission angles. Our source yields high-fidelity polarization entanglement and high pair-generation rates without any requirement for active interferometric stabilization, which makes it an ideal candidate for a variety of applications, in particular those requiring indistinguishable photons.
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We present a source of polarization entangled photon pairs based on spontaneous parametric downconversion engineered for frequency uncorrelated telecom photon generation. Our source provides photon pairs that display, simultaneously, the key properties for high-performance quantum information and fundamental quantum science tasks. Specifically, the source provides for high heralding efficiency, high quantum state purity and high entangled state fidelity at the same time. Among different tests we apply to our source we observe almost perfect non-classical interference between photons from independent sources with a visibility of (100 ± 5)%.
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