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

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∼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.

High-precision mass spectrometer for light ions

“…Therefore, the axial frequency ratio of the carbon ion and proton is fixed to the charge-to-mass ratio of these two ions. To get both ions in resonance with their respective tank circuit, the carbon axial resonator in the PT is equipped with a voltage-variable capacitor that allows fine-tuning of its resonance frequency to the ion's axial frequency in a range of 5 kHz [33,34]. The same applies for the modified cyclotron frequencies of the two ions, since the magnetic field of the superconducting magnet cannot easily be tuned to fit the ions' modified cyclotron frequencies to the resonator resonance frequency.…”

Sympathetic cooling of protons and antiprotons with a common endcap Penning trap

“…The corresponding frequencies are measured using an image current detection technique (7,13,14) and the cyclotron frequency is determined through the BrownGabrielse invariance theorem ν 2 c = ν 2 + + ν 2 z + ν 2 − (15). In addition the spin of the particle splits the energy levels by…”

“…A more serious problem comes from the necessity of measuring the axial frequencies of the two ion species to bring them into resonance in the two traps. Typically, this is achieved by connecting a tuned RLC circuit, acting as a thermal bath, in parallel to the trap as described in (13,14,36). This circuit can be shown to interact with the proton with a time constant given by:…”

Improved limit on the directly measured antiproton lifetime

“…Radiofrequency drive lines are connected to the electrodes to manipulate the trapped particles. To detect the particles, a highly-sensitive superconducting image-current detection system [15] is connected to an electrode next to the central ring electrode of the trap. This device is used for detection and resistive cooling [16] and allows for the continuous monitoring and counting of trapped antiprotons.…”