Eur. Phys. J. D (2014) 68: 139
https://doi.org/10.1140/epjd/e2014-50049-y

Regular Article

Exotic states in the dynamical Casimir effect

¹ CNISM and Center for Nonlinear and Complex Systems, Università degli Studi dell’Insubria, via Valleggio 11, 22100 Como, Italy
² Istituto Nazionale di Fisica Nucleare, Sezione di Milano, via Celoria 16, 20133 Milano, Italy
³ Department of Information Technologies, University of Milan, via Bramante 65, 26013 Crema, Italy
⁴ Department of Physics, University of Milan, via Celoria 16, 20133 Milano, Italy

^a e-mail: giuliano.benenti@uninsubria.it

Received: 16 January 2014
Received in final form: 2 March 2014
Published online: 5 June 2014

Abstract

We consider the interaction of a qubit with a single mode of the quantized electromagnetic field and show that, in the ultrastrong coupling regime and when the qubit-field interaction is switched on abruptly, the dynamical Casimir effect leads to the generation of a variety of exotic states of the field, which cannot be simply described as squeezed states. Such effect is a consequence of the intrinsic nonlinearity of the qubit and also appears when initially both the qubit and the field are in their ground state. The non-classicality of the obtained exotic states is characterized by means of a parameter based on the volume of the negative part of the Wigner function. A transition to non-classical states is observed by changing either the interaction strength or the interaction time. The observed phenomena appear as a general feature of nonadiabatic quantum gates, so that the dynamical Casimir effect can be the origin of a fundamental upper limit to the maximum speed of quantum computation and communication protocols.