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Entanglement-based single-shot detection of a single magnon with a superconducting qubit

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Science  24 Jan 2020:
Vol. 367, Issue 6476, pp. 425-428
DOI: 10.1126/science.aaz9236

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Detecting a single magnetic excitation

Quantum-enhanced sensing is one of the near-term applications for the developing field of quantum technologies. A promising approach to quantum sensing relies on entangling a well-controlled system (the sensor) to the system of interest to detect quanta of excitations in the latter. By entangling a superconducting qubit with a ferrimagnetic crystal, Lachance-Quirion et al. demonstrate that they can detect a quantum of magnetic excitation (a magnon) within the sample. The demonstration of a high-efficiency single-magnon detector will be useful for quantum sensing as well as an active component of hybrid quantum systems and should find a wide range of applications in quantum technologies.

Science, this issue p. 425

Abstract

The recent development of hybrid systems based on superconducting circuits provides the possibility of engineering quantum sensors that exploit different degrees of freedom. Quantum magnonics, which aims to control and read out quanta of collective spin excitations in magnetically ordered systems, provides opportunities for advances in both the study of magnetism and the development of quantum technologies. Using a superconducting qubit as a quantum sensor, we report the detection of a single magnon in a millimeter-sized ferrimagnetic crystal with a quantum efficiency of up to 0.71. The detection is based on the entanglement between a magnetostatic mode and the qubit, followed by a single-shot measurement of the qubit state. This proof-of-principle experiment establishes the single-photon detector counterpart for magnonics.

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