1,721,453 research outputs found
From nonequilibrium Green’s functions to quantum master equations for the density matrix and out-of-time-order correlators: Steady-state and adiabatic dynamics
No full textWe consider a finite quantum system under slow driving and weakly coupled to thermal reservoirs at different temperatures. We present a systematic derivation of the quantum master equation for the density matrix and the out-of-time-order correlators. We start from the microscopic Hamiltonian and we formulate the equations ruling the dynamics of these quantities by recourse to the Schwinger-Keldysh nonequilibrium Green’s function formalism, performing a perturbative expansion in the coupling between the system and the reservoirs. We focus on the adiabatic dynamics, which corresponds to considering the linear response in the ratio between the relaxation time due to the system-reservoir coupling and the time scale associated to the driving. We calculate the particle and energy fluxes. We illustrate the formalism in the case of a qutrit coupled to bosonic reservoirs and of a pair of interacting quantum dots attached to fermionic reservoirs, also discussing the relevance of coherent effects.Fil: Bhandari, Bibek. Consiglio Nazionale delle Ricerche; Italia. Rochester Institute of Technology; Estados UnidosFil: Fazio, Rosario. Università degli Studi di Napoli Federico II; Italia. Centro Internazionale di Fisica Teorica; Italia. Consiglio Nazionale delle Ricerche; ItaliaFil: Taddei, Fabio. Consiglio Nazionale delle Ricerche; ItaliaFil: Arrachea, Liliana del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Ciencias Físicas. - Universidad Nacional de San Martín. Instituto de Ciencias Físicas; Argentin
The power of a critical heat engine
Full text linkSince its inception about two centuries ago thermodynamics has sparkled continuous interest and fundamental questions. According to the second law no heat engine can have an efficiency larger than Carnot's efficiency. The latter can be achieved by the Carnot engine, which however ideally operates in infinite time, hence delivers null power. A currently open question is whether the Carnot efficiency can be achieved at finite power. Most of the previous works addressed this question within the Onsager matrix formalism of linear response theory. Here we pursue a different route based on finite-size-scaling theory. We focus on quantum Otto engines and show that when the working substance is at the verge of a second order phase transition diverging energy fluctuations can enable approaching the Carnot point without sacrificing power. The rate of such approach is dictated by the critical indices, thus showing the universal character of our analysis
Mott-insulating and glassy phases of polaritons in 1D arrays of coupled cavities
No full textBy means of analytical and numerical methods we analyze the phase diagram of polaritons in one-dimensional coupled cavities. We locate the phase boundary, discuss the behavior of the polariton compressibility and visibility fringes across the critical point, and find a nontrivial scaling of the phase boundary as a function of the number of atoms inside each cavity. We also predict the emergence of a polaritonic glassy phase when the number of atoms fluctuates from cavity to cavity. © 2007 The American Physical Society
Thermodynamic uncertainty relations for systems with broken time reversal symmetry: the case of superconducting hybrid systems
Full text linkWe derive bounds to the thermodynamic uncertainty relations in the
linear-response regime for steady-state transport in two-terminal systems when
time reversal symmetry is broken. We find that such bounds are different for
charge and heat currents and depend on the details of the system, through the
Onsager coefficients, and on the ratio between applied voltage and temperature
difference. As a function of such a ratio, the bounds can take any positive
values. The bounds are then calculated for a hybrid coherent superconducting
system using the scattering approach, and the concrete case of an Andreev
interferometer is explored. Interestingly, we find that the bound on the charge
current is always smaller than 2 when the system operates as a heat engine,
while the bound on the heat current is always larger than 2 when the system
operates as a refrigerator.Comment: 8 pages, 5 figure
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