Multi-photon transitions between energy levels in a current-biased Josephson tunnel junction

TL;DR

This paper experimentally investigates multi-photon transitions in a current-biased Josephson tunnel junction at low temperatures, revealing quantum tunneling and anharmonic energy level transitions induced by microwave radiation.

Contribution

It demonstrates the observation of multi-photon transitions between energy levels in a Josephson junction, highlighting quantum effects and anharmonicity at low temperatures.

Findings

Quantum tunneling observed below 280 mK.

Multi-photon transitions detected between 10 GHz and 38 GHz.

Junction potential exhibits anharmonic energy levels.

Abstract

The escape of a small current-biased Josephson tunnel junction from the zero voltage state in the presence of weak microwave radiation is investigated experimentally at low temperatures. The measurements of the junction switching current distribution indicate the macroscopic quantum tunneling of the phase below a cross-over temperature of $T^{\star} \approx 280 \rm{mK}$. At temperatures below $T^{\star}$ we observe both single-photon and \emph{multi-photon} transitions between the junction energy levels by applying microwave radiation in the frequency range between $10 \rm{GHz}$ and $38 \rm{GHz}$ to the junction. These observations reflect the anharmonicity of the junction potential containing only a small number of levels.