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

Abstract

Rich quantum effects emerge when several quantum systems are indistinguishable from the point of view of the bath they interact with. In particular, delocalised excitations corresponding to coherent superposition of excited states (reminiscent of double slit experiments or beam splitters in interferometers) appear and change drastically the dynamics and steady state of the systems. Such phenomena, which are central mechanisms of superradiance, present interesting properties for thermodynamics and potentially other quantum technologies. Indeed, a recent paper [C.L. Latune, I. Sinayskiy, F. Petruccione, Phys. Rev. A 99, 052105 (2019)] studies these properties in a pair of indistinguishable two-level systems and points out surprising effects of mitigation and amplification of the bath's action on the energy and entropy of the pair. Here, we generalise the study to ensembles of arbitrary number of spins of arbitrary size. We confirm that the previously uncovered mitigation and amplification effects remain, but also that they become more and more pronounced with growing number of spin and growing spin size. Moreover, we also investigate the free energy and the entropy production of the overall dissipation process and find dramatic reductions of irreversibility. The possibility of mitigating or amplifying the effects of the baths is highly desirable in quantum thermodynamics if one wants to optimise the use of the baths to enhance the performance of thermodynamic tasks. As illustrative application of these effects, we show explicitly the large power enhancements that can be obtained in cyclic thermal machines. The reduction of irreversibility is also a promising aspect since irreversibility is known to limit the performance of thermal machines. Beyond thermodynamics, the above findings might lead to interesting applications in state protection, quantum computational tasks, light harvesting devices, quantum biology, but also for the study of entropy production. Moreover, an experimental observation [J. M. Raimond, P. Goy, M. Gross, C. Fabre, and S. Haroche, Phys. Rev. Lett. 49, 117 (1982)] confirms that such effects are indeed within reach.observables J z and J 2 := J 2 x + J 2 y + J 2 z . Such eigenvectors are denoted by |J, m in reference to their associated eigenvalues,with −J ≤ m ≤ J and J ∈ [J 0 ; ns], where J 0 = 0 if s ≥ 1 and J 0 = 1/2 if s = 1/2 and n odd. A quick calculation shows that the natural basis contains (2s + 1) n elements whereas there are only (ns + 1) 2 (or (ns + 1/2)(ns + 3/2) when s = 1/2 and n is odd) different eigenvectors of J z and J 2 satisfying −J ≤ m ≤ J and J ∈ [J 0 ; ns]. Therefore, for n ≥ 3 degeneracies appear (some eigenvectors |J, m are repeated), meaning that different linear combinations of elements of the local basis |m 1 , ..., m n result in eigenstates of J z and J 2 with same eigenvalue J (total spin) and m (z-component of the spin). Then, we denote by |J, m i the degenerate eigenstates of J z and J 2 where the degeneracy index i runs from 1 to l J , integer which represents th...

Collective heat capacity for quantum thermometry and quantum engine enhancements

“…Finally, with respect to cyclic thermal machines -Otto engines operating close to the Carnot bound, we show that collective effects are always beneficial in terms of output power, which is a stronger result than in [19]. The largest enhancements come at high hot bath temperatures.…”

“…The largest enhancements come at high hot bath temperatures. Regarding the output work per cycle, we recover the same asymptotic scaling as in [19].…”

“…Collective couplings have also been investigated in continuous thermal machines [17,18]. Finally, in [19] it is shown that the combination of mitigation effects stemming from collective bath couplings can increase the output power of Otto engines. The present study confirms and extends the results of [19].…”

Quantum thermodynamics and quantum coherence engines

“…Accordingly, they are not classified as HECs. HECs can be converted to heat, and heat [174][175][176] can produce them.…”

Energetic advantages of nonadiabatic drives combined with nonthermal quantum states

“…All these energetic advantages rely on the availability of non-thermal states. There are indeed many realistic situations producing non-thermal states, including strong interaction with a thermal bath [42,43], manybody systems interacting with a common bath [44][45][46][47][48][49][50], non-Markovian evolution [51,52], and interaction with several thermal baths at different temperatures [53].…”