Hybrid quantum circuit with a superconducting qubit coupled to a spin ensemble

TL;DR

This paper demonstrates a hybrid quantum circuit where a superconducting qubit is coherently coupled to an ensemble of NV center spins, enabling quantum memory functionalities.

Contribution

It presents the first experimental realization of a hybrid circuit combining a superconducting qubit with a spin ensemble for quantum memory applications.

Findings

Successful coherent coupling between qubit and spin ensemble

Storage and retrieval of quantum states in the spin ensemble

First proof of concept for spin-ensemble based quantum memory

Abstract

We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back later on into the qubit. These results constitute a first proof of concept of spin-ensemble based quantum memory for superconducting qubits.