Towards a spin-ensemble quantum memory for superconducting qubits

TL;DR

This paper reviews the development of a multi-mode quantum memory combining spin ensembles with superconducting qubits, demonstrating state transfer, multi-mode retrieval, and reset techniques for long-term quantum information storage.

Contribution

It introduces a protocol for a multi-mode quantum memory and reports experimental validation using NV centers in diamond for quantum state transfer and retrieval.

Findings

Successful transfer of quantum states from qubits to spin ensemble

Multi-mode retrieval of classical microwave pulses at the single-photon level

Implementation of optical reset for the spin memory

Abstract

This article reviews efforts to build a new type of quantum device, which combines an ensemble of electronic spins with long coherence times, and a small-scale superconducting quantum processor. The goal is to store over long times arbitrary qubit states in orthogonal collective modes of the spin-ensemble, and to retrieve them on-demand. We first present the protocol devised for such a multi-mode quantum memory. We then describe a series of experimental results using NV center spins in diamond, which demonstrate its main building blocks: the transfer of arbitrary quantum states from a qubit into the spin ensemble, and the multi-mode retrieval of classical microwave pulses down to the single-photon level with a Hahn-echo like sequence. A reset of the spin memory is implemented in-between two successive sequences using optical repumping of the spins.