Dynamics of strongly coupled disordered dissipative spin-boson systems

Eliana Fiorelli,Pietro Rotondo,Federico Carollo,Matteo Marcuzzi,Igor Lesanovsky

doi:10.1103/physrevresearch.2.013198

Eliana Fiorelli, Pietro Rotondo + Show 3 more

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https://doi.org/10.1103/physrevresearch.2.013198

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Abstract

Spin-boson Hamiltonians are an effective description for numerous quantum many-body systems such as atoms coupled to cavity modes, quantum electrodynamics in circuits and trapped ion systems. While reaching the limit of strong coupling is possible in current experiments, the understanding of the physics in this parameter regime remains a challenge, especially when disorder and dissipation are taken into account. Here we investigate a regime where the many-body spin dynamics can be related to a Ising energy function defined in terms of the spin-boson couplings. While in the coherent weak coupling regime it is known that an effective description in terms of spin Hamiltonian is possible, we show that a similar viewpoint can be adopted in the presence of dissipation and strong couplings. The resulting many-body dynamics features approximately thermal regimes, separated by out-of-equilibrium ones in which detailed balance is broken. Moreover, we show that under appropriately chosen conditions one can even achieve cooling of the spin degrees of freedom. This points towards the possibility of using strongly coupled dissipative spin-boson systems for engineering complex energy landscapes together with an appropriate cooling dynamics.

Highlights

Spin-boson Hamiltonians are an effective description for numerous quantum few- and many-body systems, such as atoms coupled to cavity modes, quantum electrodynamics in circuits, and trapped ion systems
While reaching the limit of strong coupling is possible in current experiments, the understanding of the physics in this parameter regime remains a challenge, especially when disorder and dissipation are taken into account
While in the coherent weak coupling regime it is known that an effective description in terms of spin Hamiltonian is possible, we show that a similar viewpoint can be adopted in the presence of dissipation and strong couplings

Summary

INTRODUCTION

Prominent platforms for quantum simulation, such as cavity, circuit [1], or waveguide quantum electrodynamics [2] as well as trapped ions [3,4] can be modeled by ensembles of two-level systems interacting via bosonic degrees of freedom (electromagnetic modes or phonons). [10,11], instead, spin-glass techniques are employed to show that the same system effectively realizes an associative memory Most of these techniques, cannot be straightforwardly generalized to study open quantum dynamics in the strong coupling regime, and only a few studies deal with disordered open quantum systems [12,13,14,15]. Outside these the dynamics is generally nonthermal and detailed balance is broken This link between an open, strongly coupled spin-boson system and the physics of disordered Ising spin systems opens up the possibility of engineering complex classical energy landscapes—with importance in the context of optimization problems [18] or associative memories [19]—together with a cooling protocol. Since this ion is coupled to the same phonon mode as the other ions this effectively implements jump operators of the form introduced in Eq (2)

SPIN DYNAMICS AT STRONG COUPLING

LARGE η

SMALL η

THERMAL VERSUS NONTHERMAL RATES

Findings

BREAKDOWN OF DETAILED BALANCE