Abstract
We report on a universal method to measure the genuine indistinguishability of photons—a crucial parameter that determines the accuracy of optical quantum computing. Our approach relies on a low-depth cyclic multiport interferometer with modes, leading to a quantum interference fringe whose visibility is a direct measurement of the genuine -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 four-photon indistinguishability up to . 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.
- Received 31 January 2022
- Revised 6 June 2022
- Accepted 11 August 2022
DOI:https://doi.org/10.1103/PhysRevX.12.031033
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Focus
FocusMeasuring the Similarity of Photons
Published 2 September 2022
A new optical device measures photon indistinguishability—an important property for future light-based quantum computers.
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Popular Summary
To unleash the potential of photonics in quantum computing and simulation, single photons need to be generated and manipulated in large numbers. In particular, quantum information processing in photonics is typically based on quantum interference, a kind of effect that is accessible only if the photons are indistinguishable. Verifying and quantifying photon indistinguishability is thus a task of utmost importance. Here, we propose a general method to characterize the genuine indistinguishability of three or more photons.
If we have only two photons to deal with, indistinguishability is verified straightforwardly through the Hong-Ou-Mandel experiment, a kind of measurement routinely performed in quantum optics laboratories. However, when more photons are involved, assessing their indistinguishability is not trivial.
To bridge this gap, we propose an optical interferometer with a novel though simple layout, which enables the interference of an arbitrary number of single photons. First, we show theoretically that the visibility of the quantum interference fringes in this device gives a direct indication of the genuine multiphoton indistinguishability. Then, we demonstrate our ideas in experiments: We use an integrated version of our interferometer to characterize different four-photon states emitted by a quantum-dot source.
Our proposed device has the potential to become a standard characterization tool in quantum optics laboratories, allowing quick validation of multiphoton sources. In addition, the novel interference effects arising from its unconventional layout opens new prospects in understanding quantum interference and exploiting it for applications.
