Fast tuning of superconducting microwave cavities

TL;DR

This paper demonstrates rapid tuning of superconducting microwave cavities by varying a Josephson inductance, enabling fast frequency changes that surpass the cavity linewidth, with potential applications in quantum information processing.

Contribution

The authors introduce a method for fast, large-scale tuning of superconducting microwave cavities using Josephson inductance variation, achieving tuning times much shorter than the photon lifetime.

Findings

Tuning by several hundred linewidths achieved in milliseconds

Photons leak out at the new frequency after detuning

Devices are suitable for dynamic qubit coupling and amplification

Abstract

Photons are fundamental excitations of the electromagnetic field and can be captured in cavities. For a given cavity with a certain size, the fundamental mode has a fixed frequency {\it f} which gives the photons a specific "color". The cavity also has a typical lifetime $\tau$, which results in a finite linewidth $\delta${\it f}. If the size of the cavity is changed fast compared to $\tau$, and so that the frequency change $\Delta${\it f} $\gg \delta${\it f}, then it is possible to change the "color" of the captured photons. Here we demonstrate superconducting microwave cavities, with tunable effective lengths. The tuning is obtained by varying a Josephson inductance at one end of the cavity. We show data on four different samples and demonstrate tuning by several hundred linewidths in a time $\Delta t \ll \tau$. Working in the few photon limit, we show that photons stored in the cavity at one frequency will leak out from the cavity with the new frequency after the detuning. The characteristics of the measured devices make them suitable for different applications such as dynamic coupling of qubits and parametric amplification.