Środowiskowe Seminarium z Informacji i Technologii Kwantowych

Long distance quantum communication will require the use of quantum repeaters to overcome the exponential attenuation of signal with distance. One class of such repeaters utilizes quantum errorcorrection to overcome losses in the communication channel. Here we propose a novel strategy of using the bosonic Gottesman-Kitaev-Preskill (GKP) code in a two-way repeater architecture withmultiplexing. The crucial feature of the GKP code that we make use of is the fact that GKP qubits easily admit deterministic two-qubit gates, hence allowing for multiplexing without the need forgenerating large cluster states as required in previous all-photonic architectures based on discretevariable codes. Moreover, alleviating the need for such clique-clusters entails that we are no longerlimited to extraction of at most one end-to-end entangled pair from a single protocol run. In fact,thanks to the availability of the analog information generated during the measurements of the GKPqubits, we can design better entanglement swapping procedures in which we connect links based ontheir estimated quality. This enables us to use all the multiplexed links so that large number of linksfrom a single protocol run can contribute to the generation of the end-to-end entanglement. We findthat our architecture allows for high-rate end-to-end entanglement generation and is resilient toimperfections arising from finite squeezing in the GKP state preparation and homodyne detectioninefficiency. In particular we show that long-distance quantum communication over more than 1000km is possible even with less than 13 dB of GKP squeezing. We also quantify the number of GKPqubits needed for the implementation of our scheme and find that for good hardware parametersour scheme requires around 103−104 GKP qubits per repeater per protocol run.This work is available on arxiv at arXiv:2303.14923