Dynamical Lamb effect in a tunable superconducting qubit-cavity system

Abstract

A natural atom placed into a cavity with time-dependent parameters can be parametrically excited due to interaction with the quantized photon mode. One of the channels for this process is the dynamical Lamb effect, induced by a nonadiabatic modulation of the 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 (an artificial macroscopic atom) provides a unique platform for 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 the coupling nonadiabatically, it is possible to parametrically excite a qubit through a nonadiabatic modulation of the Lamb shift, even if the cavity was initially empty. The dynamics of such a coupled system is studied within the Rabi model with a time-dependent coupling constant and beyond the rotating-wave approximation. An efficient method to increase the effect through the periodic and nonadiabatic switching of the qubit-resonator coupling energy is proposed.

Parametrically driven hybrid qubit-photon systems: Dissipation-induced quantum entanglement and photon production from vacuum

“…In this paper, we consider parametric process which is generated by the periodic modulation of the qubit-cavity coupling and in presence of energy dissipation. This parametric driving is able to greatly enhance certain quantum effects, such as parametric qubit excitation via counterrotating wave terms of the Hamiltonian bringing weaklyinteracting system effectively to the regime of strong light-matter coupling [33,34,39,40]. We here show that a periodic modulation of a qubit-cavity couplings is able to generate quite high entanglement of the two qubits even in the limit of a weak interaction.…”

“…At certain moment, interaction constant G(t) starts to be modulated periodically in time. Under these conditions, counterrotating terms responsible for the dynamical Lamb effect [33], are essential to impose a dynamics of a hybrid system, since rotating wave terms are unable to change the excitation number.…”

“…For a single qubit coupled to the resonator, strongly enhanced occupation of qubit excited state is achieved, when qubit is in a resonance with the cavity and when the modulation frequency of coupling constant is twice the cavity frequency, which dramatically enhances a transition from | ↓, 0 to | ↑, 1 bringing the occupation of | ↑, 1 to large values of the order of 1 even if |G(t)| ω [33,34]. It is expected that for a two-qubit system the behavior of both qubits occupations will be qualitatively similar.…”

Algorithmic simulation of far-from-equilibrium dynamics using quantum computer

“…Besides, superconducting quantum circuits provide a unique platform to study the effects of quantum optics and nonstationary quantum electrodynamics, see, e.g., Refs. [19,20,21,22,23,24,25,26,27,28].…”

Quantum entanglement for two qubits in a nonstationary cavity

“…While the influence of the modulation of the constant of the qubit-photon interaction on excitation of the qubit was studied in Ref. 16, below we propose excitation of the qubits due to the change of the boundary conditions of the cavity. We analyze the quantum entanglement and obtain the probability of the DLE for two qubits, coupled to an optical cavity.…”