Collectively enhanced thermalization via multiqubit collisions

Abstract

We investigate the evolution of a target qubit caused by its multiple random collisions with N -qubit clusters. Depending on the cluster state, the evolution of the target qubit may correspond to its effective interaction with a thermal bath, a coherent (laser) drive, or a squeezed bath. In cases where the target qubit relaxes to a thermal state its dynamics can exhibit a quantum advantage, whereby the target-qubit temperature can be scaled up proportionally to N 2 and the thermalization time can be shortened by a similar factor, provided the appropriate coherence in the cluster is prepared by non-thermal means. We dub these effects quantum super-thermalization due to its analogies to super-radiance. Experimental realizations of these effects are suggested.

Energetic and entropic effects of bath-induced coherences

“…. Note that one recovers the result of [39] when the pair is initialised in the ground state by taking r = 1, giving an amount of steady state coherence equal to C l1 [ρ ss (β B , 1)] = 1/z(β B ) − 1. Nevertheless, we will see in the following that the sign of the coherences is essential, therefore the important quantity in this problem is c. Crucially, the coherences (and therefore c) are strictly positive as soon as r > z(β B ), strictly negative when r < z(β B ), and null when r = z(β B ).…”

“…The opposite situation is when the atoms are at the same position (or at least confined in a volume much smaller than the emission wavelength λ a = c/ω) and with parallel polarisation, 1 = 2 , so that the two bath operator B 1 and B 2 are equal: the two atoms are effectively indistinguishable to the bath. In such a situation the dissipation is given by the following dynamics [35,39] (still assuming a weak coupling with the bath),…”

“…where S ± = σ ± 1 + σ ± 2 are the collective ladder operators, and Ω I characterises the interaction strength between the two atoms (which appears due to the spatial confinement of the pair, see [35] and Appendix B). Note that the work in [39] studies the generation of coherences induced by the bath in a pair of two-level atoms considering also the above dynamics (3). However, they focus mainly on the situation where the pair is initialised in the ground state (and on the temporary impact of the atom interaction Ω I for some specific initial states).…”

“…However, they focus mainly on the situation where the pair is initialised in the ground state (and on the temporary impact of the atom interaction Ω I for some specific initial states). Moreover, all the considerations on the energetic and entropic impact on the steady state of the pair, which constitute the main contributions of our paper, are absent of [39].…”

“…Recently, a study [39] focused specifically on the amount of coherences that can be generated through bath interaction.…”