Quantum memory with millisecond coherence in circuit QED

TLDR

Advances in coherence make superconducting quantum circuits viable for fault‑tolerant computing, and highly coherent systems are needed as rapidly addressable quantum memories that maintain superior coherence. The study demonstrates a superconducting microwave cavity architecture robust against major loss sources in circuit QED. The architecture stores quantum superpositions in a resonator for milliseconds and couples strongly to a transmon qubit for MHz‑rate control, encoding, and readout. The design extends coherence time by nearly an order of magnitude and provides an ideal platform for coherent quantum optics, advancing hardware‑efficient quantum computing.

Abstract

Significant advances in coherence render superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by Josephson-junction-based artificial atoms, while maintaining superior coherence. We demonstrate a superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for storage of quantum superpositions in a resonator on the millisecond scale, while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. This extends the maximum available coherence time attainable in superconducting circuits by almost an order of magnitude compared to earlier hardware. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing in Josephson-junction-based quantum circuits.