Vibration-induced field fluctuations in a superconducting magnet

TL;DR

This study uncovers high-frequency magnetic field noise in superconducting magnets that limits qubit coherence times, and demonstrates vibration isolation as an effective method to significantly improve coherence.

Contribution

It identifies previously undocumented high-frequency magnetic field fluctuations in superconducting magnets and shows vibration isolation can enhance qubit coherence times.

Findings

High-frequency magnetic noise (10-200 Hz) limits qubit coherence.

Vibration isolation improves coherence time from ~6 ms to ~50 ms.

Field fluctuations are at the part-per-billion level.

Abstract

Superconducting magnets enable precise control of nuclear and electron spins, and are used in experiments that explore biological and condensed matter systems, and fundamental atomic particles. In high-precision applications, a common view is that that slow (<1 Hz) drift of the homogeneous magnetic field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10 Hz to 200 Hz) that limits the coherence time of 9Be+ electron-spin qubits in the 4.46 T field of a superconducting magnet. We measure a spin-echo T2 coherence time of ~6 ms for the 9Be+ electron-spin resonance at 124 GHz, limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved T2 to ~50 ms.