A cryogenic detection system at 28.9Â MHZ for the non-destructive observation of a single proton at low particle energy

A highly sensitive detection system for the non-destructive measurement of the cyclotron frequency of a single proton stored in a cryogenic Penning trap is described. The detector consists of a low noise GaAs field effect transistor amplifier combined with a copper helical resonator with high quality factor. The resonance frequency can be tuned with a GaAs-varactor diode. Connected to the Penning trap a quality factor of 1250 at 28.9 MHz is achieved. With this detection system the signal of a single proton at a cyclotron mode-energy of only 10 meV was resolved.