Relaxation to Negative Temperatures in Double Domain Systems

Abstract

We investigate the relaxation of two collective spins in double domain system, which are individually coupled to a single bosonic reservoir, by varying the total number of spins in each domain and their initial spin configurations. A particularly interesting situation occurs when the spin domains are set in an antiparallel configuration. Further for an unbalanced configuration where the number of spins are in the excited state initially is much greater than that in the ground state, the spin ensemble prepared in the ground state relaxes towards a negative-temperature state.PACS numbers: 42.50. Nn, Introduction.-In recent years, the hybridization of quantum systems has become a key technique to design and demonstrate novel quantum behaviors [1][2][3]. With the rapid progress in quantum coherent manipulation, hybrid quantum systems have now entered the regime where we can observe unexpected or rather counterintuitive behavior even in the presence of imperfections and noise [4][5][6][7]. Such hybrid systems have not only shown the capability to achieve superior properties each individual system alone cannot achieve [5,8], but they also shred light on the fundamental complexity of such quantum systems including coupling structures and decoherence mechanisms [9]. Currently a number of such hybrid systems have been proposed (and realized in some cases) with various elements coming from atomic molecular & optical systems to solid-state systems. Example include for instance, trapped ions [10], optical cavities & resonators [11,12], electron and nuclear spin ensembles in quantum dots (QD) or nitrogen-vacancy centers in diamond [13][14][15], superconducting circuits in quantum electrodynamic systems [2] and mechanical resonators [15,16]. This large diversity of component systems really allows one to explore the unique space hybridization potentially allows.

Thermodynamics from indistinguishability: Mitigating and amplifying the effects of the bath

“…The phenomenon of collective dissipation relies on the indistinguishability of the subsystems (here spins or twolevel atoms) from the point of view of the bath [6]. Such indistinguishability is in general not present naturally but can be engineered [13,[62][63][64]77] for instance by introducing an ancillary system between the spin ensemble and the bath (erasing part of the information "seen" by the bath).…”

Efficiency of a Quantum Otto Heat Engine Operating under a Reservoir at Effective Negative Temperatures

“…In 1956, Ramsey [2] studied these states theoretically, considering them as states of thermodynamic equilibrium, and discussed the consequences on the bases of thermodynamics arising from the incorporation of negative temperatures, one of them being the need for modifications of thermodynamics laws. After more than 60 years since the experiment carried out by Purcell [1], another experiment [3,4] involving negative temperatures called attention, which have triggered a discussion on the definition of equilibrium entropy in statistical mechanics, or the "Boltzmann versus Gibbs entropy" issue [5][6][7][8][9][10][11][12][13][14][15]. Recently, H. Struchtrup [16] studied this subject from a different point of view by considering states at negative temperatures as nonequilibrium states, referring to them as temperature unstable states or states with apparent negative temperatures, thus keeping unchanged the bases of thermodynamics.…”

Open quantum systems with local and collective incoherent processes: Efficient numerical simulations using permutational invariance

“…Recent studies have highlighted the rich physics that can be inferred from the properties of the Lindbladian superoperators and their spectra [36,37,218]. Other systems of ensembles of TLSs have shown collective phenomena such as synchronization, symmetry breaking, and longlived state protection [15,85,86,136,[224][225][226][227][228]. Figure 8.…”