A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub 10 mK noise temperature based on a two stage dc SQUID

TL;DR

This paper presents a highly sensitive nuclear magnetic resonance spectrometer operating near 1 MHz with a noise temperature below 10 mK, achieved through a two-stage dc SQUID sensor and optimized cooling and circuit parameters.

Contribution

The development of a NMR spectrometer with a two-stage dc SQUID sensor achieving sub-10 mK noise temperature at around 1 MHz.

Findings

Noise temperature of 7 +/- 2 mK measured at 0.884 MHz.

Energy sensitivity of 26 +/- 1 h at 1.4 K.

Optimized circuit parameters improve sensitivity and noise performance.

Abstract

We have developed a nuclear magnetic resonance spectrometer with a series tuned input circuit for measurements on samples at millikelvin temperatures based on an integrated two-stage superconducting quantum interference device current sensor, with an energy sensitivty e = 26 +/-1 h when operated at 1.4K. To maximise the sensitivity both the NMR pickup coil and tuning capacitor need to be cooled, and the tank circuit parameters should be chosen to equalise the contributions from circulating current noise and voltage noise in the SQUID. A noise temperature TN = 7 +/-2 mK was measured, at a frequency of 0.884 MHz, with the circuit parameters close to optimum.