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Quantum 2.0 Conference and Exhibition

An efficient photonic indistinguishability witness: Experimental demonstration on a photonic processor

Reinier van der Meer, Peter Hooijschuur, F. H. B. Somhorst, Pim Venderbosch, Michiel de Goede, Ben Kassenberg, Henk Snijders, Caterina Taballione, Jörn P. Epping, Hans H. van den Vlekkert, Nathan Walk, Pepijn W. H. Pinkse, Jelmer J. Renema

Published Jan 1, 2022• 0 citations
Publisher

Abstract

Efficient and reliable measurement of photonic indistinguishability is crucial for any claim of a quantum advantage in photonics. Using an integrated photonic processor, we introduce and demonstrate a semi-device-independent witness of photonic indistinguishability.
DOI
10.1364/quantum.2022.qw4b.3

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Efficient and reliable measurements of photonic indistinguishability are crucial to solidify claims of a quantum advantage in photonics. Existing indistinguishability witnesses may be vulnerable to implementation loopholes, showing the need for a measurement which depends on as few assumptions as possible. Here, we introduce a semi-device-independent witness of photonic indistinguishability and measure it on an integrated photonic processor, certifying three-photon indistinguishability in a way that is insensitive to implementation errors in our processor.
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Certification is important to guarantee the correct functioning of quantum devices. A key certification task is verifying that a device has produced a desired output state. In this work, we study this task in the context of photonic platforms, where single photons are propagated through linear optical interferometers to create large, entangled resource states for metrology, communication, quantum advantage demonstrations and for so-called linear optical quantum computing (LOQC). This setting derives its computational power from the indistinguishability of the photons, i.e., their relative overlap. Therefore, standard fidelity witnesses developed for distinguishable particles (including qubits) do not apply directly, because they merely certify the closeness to some fixed target state. We introduce a measure of fidelity suitable for this setting and show several different ways to witness it, based on earlier proposals for measuring genuine multi-photon indistinguishability. We argue that a witness based upon the discrete Fourier transform is an optimal choice. We experimentally implement this witness and certify the fidelity of several multi-photon states.
Multiphoton quantum interference is a one of the two technology platforms in which a quantum advantage has been demonstrated [1]. In these systems, a large-scale quantum state forms due to repeated effective interactions of photons (through the generalized Hong-Ou-Mandel effect) at the nodes of a photonic processor, resulting in a state that intrinsically possesses quantum complexity. A key question is how to validate the formation of a large-scale quantum state. One aspect of this is to measure whether the output quantum state is entangled – a necessary but not sufficient criterion for complexity. In this work, we derive and demonstrate an entanglement witness for large-scale optical quantum interference, and experimentally use this to demonstrate the presence of entanglement in our optical processor [2]. [1] Zhong et al., Science 370, 1460 – 1463 (2020) [2] Taballione et al., ArXiv 2012.05673 (2021)