Highly-sensitive superconducting circuits at ~700 kHz with tunable quality factors for image-current detection of single trapped antiprotons

TL;DR

This paper presents the development of superconducting circuits with high quality factors for sensitive, non-destructive detection of single antiprotons' axial frequencies, enabling improved precision in fundamental physics measurements.

Contribution

Introduction of superconducting toroidal coils with tunable quality factors for enhanced image-current detection of single antiprotons.

Findings

Quality factors up to 500,000 achieved

Signal-to-noise ratio of 30 dB at high Q factors

Superconducting switch enables continuous tuning of detector quality factor

Abstract

We developed highly-sensitive image-current detection systems based on superconducting toroidal coils and ultra-low noise amplifiers for non-destructive measurements of the axial frequencies (550$\sim$800$\,$kHz) of single antiprotons stored in a cryogenic multi-Penning-trap system. The unloaded superconducting tuned circuits show quality factors of up to 500$\,$000, which corresponds to a factor of 10 improvement compared to our previously used solenoidal designs. Connected to ultra-low noise amplifiers and the trap system, signal-to-noise-ratios of 30$\,$dB at quality factors of > 20$\,$000 are achieved. In addition, we have developed a superconducting switch which allows continuous tuning of the detector's quality factor, and to sensitively tune the particle-detector interaction. This allowed us to improve frequency resolution at constant averaging time, which is crucial for single antiproton spin-transition spectroscopy experiments, as well as improved measurements of the proton-to-antiproton charge-to-mass ratio.