Vibration-induced field fluctuations in a superconducting magnet

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 slow (<1 Hz) drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10-200 Hz) that limits the coherence time of Be-9(+) electron-spin qubits in the 4.46-T field of a superconducting magnet. We measure a spin-echo T-2 coherence time of similar to 6 ms for the Be-9(+) 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 T-2 to similar to 50 ms.