Dynamical Lamb Effect in a Tunable Superconducting Qubit-Cavity System

TL;DR

This paper explores how a tunable superconducting qubit-cavity system can be used to observe the dynamical Lamb effect, a phenomenon difficult to isolate in natural atoms, by nonadiabatically modulating the qubit-resonator coupling.

Contribution

It demonstrates the feasibility of observing the dynamical Lamb effect in superconducting circuits using time-dependent coupling modulation, extending beyond the rotating wave approximation.

Findings

Dynamical Lamb effect can be induced in superconducting qubits.

Nonadiabatic modulation enhances the effect.

Periodic switching of coupling increases excitation efficiency.

Abstract

A natural atom placed into a cavity with time-dependent parameters can be parametrically excited due to the interaction with the quantized photon mode. One of the channels of such a process is the dynamical Lamb effect, induced by a nonadiabatic modulation of atomic level Lamb shift. However, in experiments with natural atoms it is quite difficult to isolate this effect from other mechanisms of atom excitation. We point out that a transmission line cavity coupled with a superconducting qubit (artificial macroscopic atom) provides a unique platform for the observation of the dynamical Lamb effect. A key idea is to exploit a dynamically tunable qubit-resonator coupling, which was implemented quite recently. By varying nonadiabatically the coupling, it is possible to parametrically excite a qubit through a nonadiabatic modulation of the Lamb shift, even if the cavity was initially empty. A dynamics of such a coupled system is studied within the Rabi model with time-dependent coupling constant and beyond the rotating wave approximation. An efficient method to increase the effect through the periodic and nonadiabatic switching of a qubit-resonator coupling energy is proposed.