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arXiv:1003.2258 · Physical Review A

Distributed quantum computation with arbitrarily poor photon detection

Yuichiro Matsuzaki, Simon C. Benjamin, Joseph F. Fitzsimons

Published Jul 22, 2010• 6 citations
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Abstract

In a distributed quantum computer, scalability is accomplished by networking together many elementary nodes. Typically the network is optical and internode entanglement involves photon detection. In complex networks the entanglement fidelity may be degraded by the twin problems of photon loss and dark counts. Here we describe an entanglement protocol which can achieve high fidelity even when these issues are arbitrarily severe; indeed the method succeeds with finite probability even if the photon detectors are entirely removed from the network. An experimental demonstration should be possible with existing technologies.

DOI
10.1103/physreva.82.010302

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In a distributed quantum computer, scalability is accomplished by networking together many elementary nodes. Typically the network is optical and internode entanglement involves photon detection. In complex networks the entanglement fidelity may be degraded by the twin problems of photon loss and dark counts. Here we describe an entanglement protocol which can achieve high fidelity even when these issues are arbitrarily severe; indeed the method succeeds with finite probability even if the photon detectors are entirely removed from the network. An experimental demonstration should be possible with existing technologies.
In distributed quantum computation, small devices composed of a single or a few qubits are networked together to achieve a scalable machine. Typically, there is an optically active matter qubit at each node, so that photons are exploited to achieve remote entanglement. However, in many systems the optically active states are unstable or poorly defined. We report a scheme to perform a high-fidelity entanglement operation even given severe instability. The protocol exploits the existence of optically excited states for phase acquisition without actually exciting those states; it functions with or without cavities and does not require number-resolving detectors.
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The act of measuring optical emissions from two remote qubits can entangle them. By demanding that a photon from each qubit reaches the detectors, one can ensure that no photon was lost. But retaining both photons is rare when loss rates are high, as in Moehring et al. where 30 successes occurred per 10(9) attempts. We describe a means to exploit the low grade entanglement heralded by the detection of a lone photon: A subsequent perfect operation is quickly achieved by consuming this noisy resource. We require only two qubits per node, and can tolerate both path length variation and loss asymmetry. The impact of photon loss upon the failure rate is then linear; realistic high-loss devices can gain orders of magnitude in performance and thus support quantum computing.
ABSTRACT The scaling of photonic quantum technologies, including quantum networks and optical quantum computing, necessitates high‐fidelity and massively parallel single‐photon detection. While superconducting nanowire single‐photon detectors (SNSPDs) provide state‐of‐the‐art performance, their large‐scale deployment is often hindered by stringent cryogenic requirements and integration complexity. In this work, we present a parallel architecture designed to overcome the scalability bottlenecks. Experimentally, we demonstrate the largest SNSPD system to date, comprising 100 channels operating stably below 2.1 K within a compact Gifford‐McMahon cryocooler. All channels exhibit exceptional performance, achieving system detection efficiencies (SDE) between 80.1% and 98.3%, with dark count rates (DCR) maintained below 300 cps. Furthermore, leveraging this parallel capability, we demonstrate a fully connected multi‐user quantum entanglement distribution network. This work establishes a robust and scalable infrastructure, paving the way for large‐scale quantum photonic applications.
We analyze the generation of entanglement in a multipartite optical network. We generalize the twin-field strategy to the multipartite case and show that our protocol has advantageous rate-loss scalings of distributing WWW states and Dicke states over the star networks. We provide precise theoretical formulas and quantitative performance analyses. Also, analysis of the same protocol using Gaussian states as resources, which is a typical setup in many experimental tests, is provided. We numerically study the feasibility of the protocol in realistic experimental conditions with imperfect detectors. We observe that the advantage depends on the chosen fidelity and is affected by the dark counts of the detector.