Three-qubit refrigerator with two-body interactions.

We propose a three-qubit setup for the implementation of a variety of quantum thermal machines where all heat fluxes and work production can be controlled. An important configuration that can be designed is that of an absorption refrigerator, extracting heat from the coldest reservoir without the need of external work supply. Remarkably, we achieve this regime by using only two-body interactions instead of the widely employed three-body interactions.

Classical emulation of quantum-coherent thermal machines.

The performance enhancements observed in various models of continuous quantum thermal machines have been linked to the buildup of coherences in a preferred basis. But is this connection always an evidence of "quantum-thermodynamic supremacy"? By force of example, we show that this is not the case. In particular, we compare a power-driven three-level continuous quantum refrigerator with a four-level combined cycle, partly driven by power and partly by heat.

Internal dissipation and heat leaks in quantum thermodynamic cycles.

The direction of the steady-state heat currents across a generic quantum system connected to multiple baths may be engineered to realize virtually any thermodynamic cycle. In spite of their versatility, such continuous energy-conversion systems are generally unable to operate at maximum efficiency due to non-negligible sources of irreversible entropy production. In this paper we introduce a minimal model of irreversible absorption chiller.

Optimal performance of endoreversible quantum refrigerators.

The derivation of general performance benchmarks is important in the design of highly optimized heat engines and refrigerators. To obtain them, one may model phenomenologically the leading sources of irreversibility ending up with results that are model independent, but limited in scope. Alternatively, one can take a simple physical system realizing a thermodynamic cycle and assess its optimal operation from a complete microscopic description.

Quantum-enhanced absorption refrigerators.

Thermodynamics is a branch of science blessed by an unparalleled combination of generality of scope and formal simplicity. Based on few natural assumptions together with the four laws, it sets the boundaries between possible and impossible in macroscopic aggregates of matter. This triggered groundbreaking achievements in physics, chemistry and engineering over the last two centuries.

Performance bound for quantum absorption refrigerators.

An implementation of quantum absorption chillers with three qubits has been recently proposed that is ideally able to reach the Carnot performance regime. Here we study the working efficiency of such self-contained refrigerators, adopting a consistent treatment of dissipation effects. We demonstrate that the coefficient of performance at maximum cooling power is upper bounded by 3/4 of the Carnot performance.

Effects of classical nonlinear resonances in grazing diatom-surface collisions.

Energy transfer between vibrational, rotational, and translational degrees of freedom of a molecule during a collision process is enhanced when the classical frequencies associated with the initial state are in the proximity of nonlinear resonance conditions. We present an analysis of the classical resonant effects in the collisions of light diatoms with periodic surfaces, and discuss the initial conditions in which these effects can be observed. In particular, we find that for grazing incidence and resonant initial values of the classical frequencies, corresponding to specific vibro-rotational molecular states and translational energies, an efficient energy transfer between the intramolecular vibro-rotational degrees of freedom and the translational degree of freedom along a symmetry direction on the surface can be found.

Nearly resonant multidimensional systems under a transient perturbative interaction.

We analyze the response of a classical system with N>or=2 internal degrees of freedom satisfying R View Article and Find Full Text PDF

Quantum computing by an optimal control algorithm for unitary transformations.

Quantum computation is based on implementing selected unitary transformations representing algorithms. A generalized optimal control theory is used to find the driving field that generates a prespecified unitary transformation. The approach is independent of the physical implementation of the quantum computer and it is illustrated for one and two qubit gates in model molecular systems, where only part of the Hilbert space is used for computation.