Negative-temperature-state relaxation and reservoir-assisted quantum entanglement in double-spin-domain systems

Abstract

Spin collective phenomena including superradiance are even today being intensively investigated with experimental tests performed based on state-of-the-art quantum technologies. Such attempts are not only for the simple experimental verification of predictions from the last century but also as a motivation to explore new applications of spin collective phenomena and the coherent control of the coupling between spin ensembles and reservoirs. In this paper, we investigate the open quantum dynamics of two spin ensembles (double spin domains) coupled to a common bosonic reservoir. We analyze in detail the dynamics of our collective state and its structure by focusing on both the symmetry and asymmetry of this coupled spin system. We find that when the spin size of one of the double domains is larger than that of the other domain, at the steady state this system exhibits two novel collective behaviors: the negative-temperature state relaxation in the smaller spin domain and the reservoir-assisted quantum entanglement between the two domains. These results are the consequence of the asymmetry of this system and the decoherence driven by the common reservoir.

Relaxation dynamics in double-spin systems

“…As was pointed out recently in Ref. [36,37] rise to new and interesting effects such as the possibility of relaxing certain initial states not into the ground state but rather into an excited state. When considering only the smaller of the two spins in this nonequilibrium state, one observes an occupation inversion that can, in principle, be interpreted in the framework of negative temperatures [38][39][40].…”

“…This counterintuitive behavior has been noticed previously in Refs. [36,37]. It arises because the Hamiltonian (3) takes the form H int = k g L,k,1 S + tot b k,1 + g * L,k,1 S − tot b † k,1 for symmetric couplings (g L,k,1 = g R,k,1 ) such that the total angular momentum is conserved.…”

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.…”

“…It has been shown in Refs. [86,228] that if N 1 ≠ N 2 , and both ensembles are driven and can dissipate only through a common channel, a peculiar exchange of spin inversion can be engineered in the system. We will consider a generalization of the collective dynamics considered in Ref.…”

Reservoir-assisted energy migration through multiple spin-domains

“…Introduction-Nature has developed many methods for the transport of energy on length scales ranging from the atomic to cosmological [1][2][3][4]. Photosynthesis is one extremely well known example where pigment cofactors absorb the light and transfer it to antennae pigments where it is converted to chemical energy [5][6][7][8][9][10][11][12][13].…”