Compact 3D quantum memory

TL;DR

This paper demonstrates a compact 3D quantum memory device using a transmon coupled to two modes of a single cavity, achieving a sixfold increase in lifetime with high fidelity, advancing scalable quantum information storage.

Contribution

It introduces a scalable, compact 3D quantum memory design utilizing multimode cavities and second-order protocols for enhanced lifetime and fidelity.

Findings

Achieved a sixfold increase in quantum memory lifetime.

Realized approximately 80% fidelity via quantum process tomography.

Demonstrated that lifetime enhancement is not limited by fundamental constraints.

Abstract

Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit both to a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. The external coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of $6$ with a fidelity of approximately $80\%$ determined via quantum process tomography. We also find that this enhancement is not limited by fundamental constraints.