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arXiv:1508.01587 · Scientific Reports

Experimental demonstration of a quantum router

Xinxing Yuan, J.-J. Ma, Pan‐Yu Hou, X.-Y. Chang, Chong Zu, L-M Duan

Published Jul 22, 2015• 59 citations
arXivHTMLPDF

Abstract

The router is a key element for a network. We describe a scheme to realize genuine quantum routing of single-photon pulses based on cascading of conditional quantum gates in a Mach-Zehnder interferometer and report a proof-of-principle experiment for its demonstration using linear optics quantum gates. The polarization of the control photon routes in a coherent way the path of the signal photon while preserving the qubit state of the signal photon represented by its polarization. We demonstrate quantum nature of this router by showing entanglement generated between the initially unentangled control and signal photons, and confirm that the qubit state of the signal photon is well preserved by the router through quantum process tomography.

DOI
10.1038/srep12452

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The router is a key element for a network. We describe a scheme to realize genuine quantum routing of single-photon pulses based on cascading of conditional quantum gates in a Mach-Zehnder interferometer and report a proof-of-principle experiment for its demonstration using linear optics quantum gates. The polarization of the control photon routes in a coherent way the path of the signal photon while preserving the qubit state of the signal photon represented by its polarization. We demonstrate quantum nature of this router by showing entanglement generated between the initially unentangled control and signal photons, and confirm that the qubit state of the signal photon is well preserved by the router through quantum process tomography.
We report an experiment that demonstrates full function of a quantum router using entangled photons, where the paths of a single-photon pulse are controlled in a coherent fashion by polarization of another single photon. Through a projective measurement, we prepare the polarization of the control photon in arbitrary superposition states, leading to coherent routing of the target photon in quantum superposition of different paths. We demonstrate quantum nature of this router through optical measurements based on quantum state tomography and show an average fidelity of (93.24±0.23)(93.24\pm 0.23)%(93.24±0.23) for the quantum routing operation.
A quantum router is an elementary building block for quantum-information processing. It directs the incoming quantum signal to different routes with phase coherence. To realize scalable quantum routing, a single particle needs to deterministically and coherently route the paths of a flying qubit, which requires nonlinear interaction at the single quantum level and complicated path-data qubit control so far beyond the experimental reach. Here we demonstrate a deterministic quantum router working at microwave frequencies based on superconducting circuits, which can naturally integrate with a leading platform for quantum computing. We encode the quantum signal into a weak coherent pulse and use an entanglement witness to rigorously verify the generated entanglement between the control qubit and the path of the data qubit, thus proving quantum coherence of the routing operation. Our experiment lays the foundation for useful applications of quantum routers in quantum networks and quantum random-access memories.
For several decades, scientists have been aware of significant benefits allowing quantum information processing technologies to surpass their classical counterparts. Recent technological development allows these benefits to be tested experimentally and in some cases also implemented in practical devices. So far the majority of experimental quantum networks was limited to peer-to-peer communications between two parties. Practical implementation of quantum communications networks, however, needs to address the problem of scalability to serve large numbers of users. Similarly to classical computer networks, their quantum counterparts would require routing protocols to direct the signal from its source to destination. Devices implementing these routing protocols are called quantum routers and have recently been subject of an intense research. In this paper, we report on experimental implementation of a linear-optical quantum router. Our device allows single-photon polarization-encoded qubits to be routed coherently into two spatial output modes depending on the state of two identical control qubits. The polarization qubit state of the routed photon is maintained during the routing operation. The success probability of our scheme can be increased up to 25% making it the most efficient linear-optical quantum router developed to this date.
Inspired by teleportation, we find that the GHZ state can be used to realize the quantum routing. This paper presents a scheme for optical implementation of a quantum router. The device directs the signal photonic qubit according to the control information. First we describe our proposal, showing the exact principle of operation on a optical scheme, the polarization state of the signal photon is undisturbed by control information under the routing operation, and the success probability can nearly reach up to 1/2. Subsequently, we discuss generalization of the scheme with multiple output ports, showing how to route signal qubit to any of the outputs.
An all-linear-optical scheme for a fully featured quantum router is presented. This device directs the signal photonic qubit according to the state of one control photonic qubit. In the introduction we formulate the list of requirements imposed on a fully quantum router. Then we describe our proposal, showing the exact principle of operation on a linear-optical scheme. Subsequently we provide a generalization of the scheme in order to optimize the success probability by means of a tunable controlled-phase gate. Finally, we show how one can modify the device to route multiple signal qubits using the same control qubit.
Abstract In photonic quantum applications, optical routers are required to handle single photons with low loss, high speed, and preservation of their quantum states. Single-photon routing with maintained polarization states is particularly important for utilizing them as qubits. Here, we demonstrate a polarization-maintaining electro-optic router compatible with single photons. Our custom electro-optic modulator is embedded in a configuration of a Mach–Zehnder interferometer, where each optical component achieves polarization-maintaining operation. We observe the performance of the router with 2%–4% loss, 20 dB switching extinction ratio, 2.9 ns rise time, and >99% polarization process fidelity to an ideal identity operation.