Scalable Generation of Multiphoton Entangled States by Active Feed-Forward and Multiplexing

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Scalable Generation of Multiphoton Entangled States by Active Feed-Forward and Multiplexing

Evan Meyer-Scott, Nidhin Prasannan, Ish Dhand, Christof Eigner, Viktor Quiring, Sonja Barkhofen, Benjamin Brecht, Martin B. Plenio, and Christine Silberhorn

Phys. Rev. Lett. 129, 150501 – Published 5 October 2022

See synopsis: A Quantum Entanglement Assembly Line

Abstract

Multiphoton entangled quantum states are key to advancing quantum technologies such as multiparty quantum communications, quantum sensing, or quantum computation. Their scalable generation, however, remains an experimental challenge. Current methods for generating these states rely on stitching together photons from probabilistic sources, and state generation rates drop exponentially in the number of photons. Here, we implement a system based on active feed-forward and multiplexing that addresses this challenge. We demonstrate the scalable generation of four-photon and six-photon Greenberger-Horne-Zeilinger states, increasing generation rates by factors of 9 and 35, respectively. This is consistent with the exponential enhancement compared to the standard nonmultiplexed approach that is predicted by our theory. These results facilitate the realization of practical multiphoton protocols for photonic quantum technologies.

Received 21 June 2022
Accepted 26 August 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.150501

Physics Subject Headings (PhySH)

Entanglement production Optical quantum information processing Quantum computation Quantum entanglement Quantum information architectures & platforms Quantum networks Quantum optics

Quantum Information, Science & Technology

synopsis

A Quantum Entanglement Assembly Line

Published 5 October 2022

A new experiment generates entanglement between many photons with a much higher probability than available methods, which could be a boon for quantum information applications.

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Authors & Affiliations

Evan Meyer-Scott¹, Nidhin Prasannan¹, Ish Dhand ², Christof Eigner ¹, Viktor Quiring¹, Sonja Barkhofen^1,*, Benjamin Brecht ¹, Martin B. Plenio ², and Christine Silberhorn ¹

¹Paderborn University, Integrated Quantum Optics, Institute for Photonic Quantum Systems (PhoQS), 33098 Paderborn, Germany
²Institut für Theoretische Physik and Center for Integrated Quantum Science and Technology (IQST), University of Ulm, 89069 Ulm, Germany

^*sonja.barkhofen@uni-paderborn.de

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Issue

Vol. 129, Iss. 15 — 7 October 2022

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Images

Figure 1
(a) Operating principle of our approach. Bell pairs are generated sequentially. The detection of one photon triggers the feed-forward including a field programmable gate array (FPGA), which in turn controls the operation mode of an all-optical storage loop. Possible operation modes are “read in and read out” (orange), “Storage” (green), or “PBS interference” (purple) selected by an appropriate switching of the electro-optic modulator (EOM). $2 N$ -fold coincidences confirm the buildup of $2 N$ -photon GHZ states. (b) Sketch of the experimental setup. A Ti:sapphire laser with a wavelength of 775 nm pumps a polarization Bell-state source based on parametric down-conversion in a Sagnac configuration (blue area). One photon of each emitted Bell pair is detected and triggers the feed-forward (red arrows), and the other photon is sent to our all-optical storage loop (green area), where it is stored until it is brought to interference with the subsequent qubit. For more information, please see the text.
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Figure 2
(a) Raw coincidence count data for four-photon GHZ state for $M = 2$ sources (see Supplemental Material Fig. S8 [36] for the six-photon data). (b) Total and storage efficiency of the all-optical storage loop. We obtain a storage efficiency of 91% with a corresponding lifetime of 131 ns. (c) Average polarization single-qubit fidelity, that is, fidelity of a retrieved polarization qubit with respect to its initial state averaged over many input polarizations, and entangled-pair fidelity after storage. For up to 20 round-trips in the storage loop, the fidelities stay roughly constant. We note that the entanglement fidelity is limited by the performance of the Bell-state source. (d) Generation rate enhancement for four- and six-photon GHZ states as a function of the number of successive uses of the Bell-state source $M$ . The observed saturation is due to the limited efficiency of the storage loop. We find an enhancement of up to a factor 35 for six-photon GHZ states. The inset displays the state fidelities, which stay constant regardless of the number of multiplexed sources. For more information, see the text.
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Figure 3
Calculated rate enhancement as a function of the Bell-pair production probability and the memory efficiency for $N = 2$ , 3, 4, 5, 6, 10 Bell pairs and optimized $M$ parameter. Our measurements for $N = 2$ and $N = 3$ (blue crosses) are well described by the theory (in the experiment, we used up to $M = 22$ time-multiplexed sources). Larger states are predicted by the same theory to experience stronger enhancement, up to 9 orders of magnitude for $N = 6$ , that is, 12-photon GHZ states, the actual state of the art. For more information on the expected absolute rates, see Supplemental Material S4 [36].
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