3,434 research outputs found
Model Studies on the Quantum Jarzynski Relation
We study the quantum Jarzynski relation for driven quantum models embedded in
various environments. We do so by generalizing a proof presented by Mukamel
[Phys. Rev. Lett 90, 170604 (2003)] for closed quantum systems. In this way, we
are able to prove that the Jarzynski relation also holds for a bipartite system
with microcanonical coupling. Furthermore, we show that, under the assumption
that the interaction energy remains constant during the whole process, the
relation is valid even for canonical coupling. The same follows for open
quantum systems at high initial temperatures up to third order of the inverse
temperature. Our analytical study is complemented by a numerical investigation
of a special model system.Comment: 7 figure
Non Thermal Equilibrium States of Closed Bipartite Systems
We investigate a two-level system in resonant contact with a larger
environment. The environment typically is in a canonical state with a given
temperature initially. Depending on the precise spectral structure of the
environment and the type of coupling between both systems, the smaller part may
relax to a canonical state with the same temperature as the environment (i.e.
thermal relaxation) or to some other quasi equilibrium state (non thermal
relaxation). The type of the (quasi) equilibrium state can be related to the
distribution of certain properties of the energy eigenvectors of the total
system. We examine these distributions for several abstract and concrete (spin
environment) Hamiltonian systems, the significant aspect of these distributions
can be related to the relative strength of local and interaction parts of the
Hamiltonian.Comment: RevTeX, 8 pages, 13 figure
Quantum-state tomography for spin-l systems
We show that the density matrix of a spin-l system can be described entirely
in terms of the measurement statistics of projective spin measurements along a
minimum of 4l+1 different spin directions. It is thus possible to represent the
complete quantum statistics of any N-level system within the spherically
symmetric three dimensional space defined by the spin vector. An explicit
method for reconstructing the density matrix of a spin-1 system from the
measurement statistics of five non-orthogonal spin directions is presented and
the generalization to spin-l systems is discussed.Comment: 10 pages, including 2 tables, minor modifications in section II,
final version for publication in Phys. Rev.
Local effective dynamics of quantum systems: A generalized approach to work and heat
By computing the local energy expectation values with respect to some local
measurement basis we show that for any quantum system there are two
fundamentally different contributions: changes in energy that do not alter the
local von Neumann entropy and changes that do. We identify the former as work
and the latter as heat. Since our derivation makes no assumptions on the system
Hamiltonian or its state, the result is valid even for states arbitrarily far
from equilibrium. Examples are discussed ranging from the classical limit to
purely quantum mechanical scenarios, i.e. where the Hamiltonian and the density
operator do not commute.Comment: 5 pages, 1 figure, published versio
Quantum control by compensation of quantum fluctuations
We show that the influence of quantum fluctuations in the electromagnetic
field vacuum on a two level atom can be measured and consequently compensated
by balanced homodyne detection and a coherent feedback field. This compensation
suppresses the decoherence associated with spontaneous emission for a specific
state of the atomic system allowing complete control of the coherent state of
the system.Comment: 5 pages RevTex and 2 figures, to be published in Optics Expres
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