3,491 research outputs found
Optical properties of a Quantum-Dot Cascade Structure
We report on our theoretical studies of the luminescence spectra of a quantum
cascade laser where the quantum wells in the active regions are replaced by
parabolic quantum dots. We analyze the influence of shape and size of the dots
on the luminescence spectra. The emission spectra have interaction induced
blueshift which increases almost linearly with increasing electron number. The
blueshift is smaller for larger and non-circular dots. For large dots, shape of
the emission line has weak dependence on the shape of quantum dots.Comment: 4 pages, 4 figure
Gibbs-Preserving Maps outperform Thermal Operations in the quantum regime
In this brief note, we compare two frameworks for characterizing possible
operations in quantum thermodynamics. One framework considers Thermal
Operations---unitaries which conserve energy. The other framework considers all
maps which preserve the Gibbs state at a given temperature. Thermal Operations
preserve the Gibbs state; hence a natural question which arises is whether the
two frameworks are equivalent. Classically, this is true---Gibbs-Preserving
Maps are no more powerful than Thermal Operations. Here, we show that this no
longer holds in the quantum regime: a Gibbs-Preserving Map can generate
coherent superpositions of energy levels while Thermal Operations cannot. This
gap has an impact on clarifying a mathematical framework for quantum
thermodynamics.Comment: 4 pages, 1 figur
Microcanonical and resource-theoretic derivations of the thermal state of a quantum system with noncommuting charges
The grand canonical ensemble lies at the core of quantum and classical
statistical mechanics. A small system thermalizes to this ensemble while
exchanging heat and particles with a bath. A quantum system may exchange
quantities represented by operators that fail to commute. Whether such a system
thermalizes and what form the thermal state has are questions about truly
quantum thermodynamics. Here we investigate this thermal state from three
perspectives. First, we introduce an approximate microcanonical ensemble. If
this ensemble characterizes the system-and-bath composite, tracing out the bath
yields the system's thermal state. This state is expected to be the equilibrium
point, we argue, of typical dynamics. Finally, we define a resource-theory
model for thermodynamic exchanges of noncommuting observables. Complete
passivity---the inability to extract work from equilibrium states---implies the
thermal state's form, too. Our work opens new avenues into equilibrium in the
presence of quantum noncommutation.Comment: Published version. 7 pages (2 figures) + appendices. The leading
author's surname is "Yunger Halpern.
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