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Quantum Information and Measurement (QIM)

Quantifying n-photon Indistinguishability with an Integrated Multi-Port Interferometer

Sarah E. Thomas, Mathias Pont, Riccardo Albiero, Nicolò Spagnolo, Francesco Ceccarelli, Giacomo Corrielli, Alexandre Brieussel, Niccolò Somaschi, Nadia Belabas, Hêlio Huet, Abdelmounaïm Harouri, Aristide Lemaître, Isabelle Sagnes, Fabio Sciarrino, Roberto Osellame, P. Senellart, Andrea Crespi

Published Jan 1, 2021• 0 citations
Publisher

Abstract

We introduce a novel method to directly characterize the indistinguishability of a state of multiple photons using a multiport interferometer. We demonstrate this method using four photons from a quantum dot single-photon source.
DOI
10.1364/qim.2021.f1c.3

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We report on a universal method to measure the genuine indistinguishability of n photons-a crucial parameter that determines the accuracy of optical quantum computing.Our approach relies on a low-depth cyclic multiport interferometer with N ¼ 2n modes, leading to a quantum interference fringe whose visibility is a direct measurement of the genuine n-photon indistinguishability.We experimentally demonstrate this technique for an eight-mode integrated interferometer fabricated using femtosecond laser micromachining and four photons from a quantum dot single-photon source.We measure a fourphoton indistinguishability up to 0.81 Æ 0.03.This value decreases as we intentionally alter the photon pairwise indistinguishability.The low-depth and low-loss multiport interferometer design provides an original path to evaluate the genuine indistinguishability of resource states of increasing photon number.
Multiphoton indistinguishability is a key resource for photonic quantum technologies, yet its characterization typically relies on resource-intensive methods. In this work, we develop two efficient and experimentally friendly protocols to estimate or bound the fidelity FindF_{\mathrm{ind}}Find​ of an NNN-photon state to the closest perfectly indistinguishable state. The first protocol applies to sources preparing separable states, uses a single Fourier interferometer together with photon-number-resolving detection, and yields tight two-sided bounds on FindF_{\mathrm{ind}}Find​. The second protocol combines randomized implementations of linear-optical interferometers with photon counting, enabling direct estimation of FindF_{\mathrm{ind}}Find​ for arbitrary NNN-photon states. Both protocols can certify Find=1−O(ε)F_{\mathrm{ind}} = 1 - \mathcal{O}(ε)Find​=1−O(ε) using provably optimal O(1/ε)\mathcal{O}(1/ε)O(1/ε) samples, in contrast to previous approaches which required prior assumptions on the model of partial distinguishability. Our methods, based on a multiphoton generalization of the Hong-Ou-Mandel test, bring the rigorous and operationally meaningful certification of multiphoton indistinguishability within reach of current photonic technologies.
Multiphoton indistinguishability is a central resource for quantum enhancement in sensing and computation. Developing and certifying large-scale photonic devices requires reliable and accurate characterization of this resource, preferably using methods that are robust against experimental errors. Here, we propose a set of methods for the characterization of multiphoton indistinguishability, based on measurements of bunching and photon-number variance. Our methods are robust in a semi-device-independent way, in the sense of being effective even when the interferometers are incorrectly dialed. We demonstrate the effectiveness of this approach using an advanced photonic platform comprising a quantum dot single-photon source and a universal fully programmable integrated photonic processor. Our results show the practical usefulness of our methods, providing robust certification tools that can be scaled up to larger systems.
Abstract Photon indistinguishability plays a fundamental role in information processing, with applications such as linear-optical quantum computation and metrology. It is then necessary to develop appropriate tools to quantify the amount of this resource in a multiparticle scenario. Here we report a four-photon experiment in a linear-optical interferometer designed to simultaneously estimate the degree of indistinguishability between three pairs of photons. The interferometer design dispenses with the need of heralding for parametric down-conversion sources, resulting in an efficient and reliable optical scheme. We then use a recently proposed theoretical framework to quantify four-photon indistinguishability, as well as to obtain bounds on three unmeasured two-photon overlaps. Our findings are in high agreement with the theory, and represent a new resource-effective technique for the characterization of multiphoton interference.
The generation of quantum states of many indistinguishable photons is a crucial resource for the realization of photonic computer architectures that can enable a quantum speedup and create fault-tolerant multi-party quantum networks. On the experimental side, the measurement of indistinguishability for a multi-photon state is a challenging task. In the case of a two-photon state, the photon indistinguishability is fully assessed by the visibility of the interference fringe of the Hong-Ou-Mandel (HOM) interference experiment on a balanced beam splitter. However, pairwise HOM experiments are unable to completely determine the multi-photon indistinguishability when more than two photons are involved [1]–[2].