Multi-mode storage and retrieval of microwave fields in a spin ensemble

TL;DR

This paper demonstrates a hybrid quantum memory system using NV centers in diamond coupled to a superconducting resonator, achieving long storage times for microwave fields through refocusing techniques, with significant improvements over prior work.

Contribution

First implementation of refocusing-based quantum memory with NV centers coupled to superconducting resonators, enabling long storage times for microwave pulses.

Findings

Stored and retrieved microwave pulses after 35 microseconds

Achieved three orders of magnitude improvement in storage time

Enabled multiple pulse storage at picoWatt power levels

Abstract

A quantum memory at microwave frequencies, able to store the state of multiple superconducting qubits for long times, is a key element for quantum information processing. Electronic and nuclear spins are natural candidates for the storage medium as their coherence time can be well above one second. Benefiting from these long coherence times requires to apply the refocusing techniques used in magnetic resonance, a major challenge in the context of hybrid quantum circuits. Here we report the first implementation of such a scheme, using ensembles of nitrogen-vacancy (NV) centres in diamond coupled to a superconducting resonator, in a setup compatible with superconducting qubit technology. We implement the active reset of the NV spins into their ground state by optical pumping and their refocusing by Hahn echo sequences. This enables the storage of multiple microwave pulses at the picoWatt level and their retrieval after up to $35 \mu$s, a three orders of magnitude improvement compared to previous experiments.