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arXiv:1807.00383 · Physical Review Letters

Polarization Entanglement by Time-Reversed Hong-Ou-Mandel Interference

Yuanyuan Chen, Sebastian Ecker, Sören Wengerowsky, Lukas Bulla, Siddarth Koduru Joshi, Fabian Steinlechner, Rupert Ursin

Published Nov 14, 2018• 63 citations

Abstract

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.

DOI: 10.1103/physrevlett.121.200502

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Quantum interference, like Hong-Ou-Mandel interference, has played an important role to test fundamental concepts in quantum physics. We experimentally show that the multiple quantum interference effects enable the generation of high-performance polarization entangled photons. These photons have a high-emission rate, are degenerate, have a broadband distribution, and are postselection free. A quantum interferometric scheme, based on a round-trip configuration of a double-pass polarization Sagnac interferometer, makes it possible to use the large generation efficiency of polarization entangled photons in the process of parametric down-conversion and to separate degenerate photon pairs into different optical modes with no requirement of postselection. We demonstrate experimentally that multiple quantum interference is not only an interesting fundamental quantum optical phenomenon but can be used for novel photonic quantum information technologies.

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 \pm 0.01) \%

polarization entanglement visibility,

(96.3 \pm 0.6) \%

successive-photon Hong-Ou-Mandel interference visibility,

(68.0 \pm 0.1

) \% heralded efficiency as detected, and

(88.6 \pm 0.2) \%

interference visibility with a local oscillator. This simultaneous achievement of state-of-the-art metrics demonstrates an adaptable platform for quantum networking.