31,889 research outputs found
Quantum fluctuation theorems and power measurements
Work in the paradigm of the quantum fluctuation theorems of Crooks and
Jarzynski is determined by projective measurements of energy at the beginning
and end of the force protocol. In analogy to classical systems, we consider an
alternative definition of work given by the integral of the supplied power
determined by integrating up the results of repeated measurements of the
instantaneous power during the force protocol. We observe that such a
definition of work, in spite of taking account of the process dependence, has
different possible values and statistics from the work determined by the
conventional two energy measurement approach (TEMA). In the limit of many
projective measurements of power, the system's dynamics is frozen in the power
measurement basis due to the quantum Zeno effect leading to statistics only
trivially dependent on the force protocol. In general the Jarzynski relation is
not satisfied except for the case when the instantaneous power operator
commutes with the total Hamiltonian at all times. We also consider properties
of the joint statistics of power-based definition of work and TEMA work in
protocols where both values are determined. This allows us to quantify their
correlations. Relaxing the projective measurement condition, weak continuous
measurements of power are considered within the stochastic master equation
formalism. Even in this scenario the power-based work statistics is in general
not able to reproduce qualitative features of the TEMA work statistics.Comment: 26 pages, 9 figure
Nonlinear Phenomena of Ultracold Atomic Gases in Optical Lattices: Emergence of Novel Features in Extended States
The system of a cold atomic gas in an optical lattice is governed by two
factors: nonlinearity originating from the interparticle interaction, and the
periodicity of the system set by the lattice. The high level of controllability
associated with such an arrangement allows for the study of the competition and
interplay between these two, and gives rise to a whole range of interesting and
rich nonlinear effects. This review covers the basic idea and overview of such
nonlinear phenomena, especially those corresponding to extended states. This
includes "swallowtail" loop structures of the energy band, Bloch states with
multiple periodicity, and those in "nonlinear lattices", i.e., systems with the
nonlinear interaction term itself being a periodic function in space.Comment: 39 pages, 21 figures; review article to be published in a Special
Issue of Entropy on "Non-Linear Lattice
How Rare Are Extraterrestrial Civilizations and When Did They Emerge?
It is shown that, contrary to an existing claim, the near equality between
the lifetime of the sun and the timescale of biological evolution on earth does
not necessarily imply that extraterrestrial civilizations are exceedingly rare.
Furthermore, on the basis of simple assumptions it is demonstrated that a near
equality between these two timescales may be the most probable relation. A
calculation of the cosmic history of carbon production which is based on the
recently determined history of the star formation rate suggests that the most
likely time for intelligent civilizations to emerge in the universe, was when
the universe was already older then about 10 billion years (for an assumed
current age of about 13 billion years).Comment: 11 pages (including 2 figures), accepted for publication in
Astrophys. Journa
Quantum Performance of Thermal Machines over Many Cycles
The performance of quantum heat engines is generally based on the analysis of
a single cycle. We challenge this approach by showing that the total work
performed by a quantum engine need not be proportional to the number of cycles.
Furthermore, optimizing the engine over multiple cycles leads to the
identification of scenarios with a quantum enhancement. We demonstrate our
findings with a quantum Otto engine based on a two-level system as the working
substance that supplies power to an external oscillator.Comment: 5 pages, 3 figures; published in Phys. Rev. Lett. as an Editors'
Suggestio
Determination of S17(0) from published data
The experimental landscape for the 7Be+p radiative capture reaction is
rapidly changing as new high precision data become available. We present an
evaluation of existing data, detailing the treatment of systematic errors and
discrepancies, and show how they constrain the astrophysical S factor (S17),
independent of any nuclear structure model. With theoretical models robustly
determining the behavior of the sub-threshold pole, the extrapolation error can
be reduced and a constraint placed on the slope of S17. Using only radiative
capture data, we find S17(0) = 20.7 +/- 0.6 (stat) +/- 1.0 (syst) eV b if data
sets are completely independent, while if data sets are completely correlated
we find S17(0) = 21.4 +/- 0.5 (stat) +/- 1.4 (syst) eV b. The truth likely lies
somewhere in between these two limits. Although we employ a formalism capable
of treating discrepant data, we note that the central value of the S factor is
dominated by the recent high precision data of Junghans et al., which imply a
substantially higher value than other radiative capture and indirect
measurements. Therefore we conclude that further progress will require new high
precision data with a detailed error budget.Comment: 10 pages, 1 figure published versio
A dynamical description of neutron star crusts
Neutron Stars are natural laboratories where fundamental properties of matter
under extreme conditions can be explored. Modern nuclear physics input as well
as many-body theories are valuable tools which may allow us to improve our
understanding of the physics of those compact objects.
In this work the occurrence of exotic structures in the outermost layers of
neutron stars is investigated within the framework of a microscopic model. In
this approach the nucleonic dynamics is described by a time-dependent mean
field approach at around zero temperature. Starting from an initial crystalline
lattice of nuclei at subnuclear densities the system evolves toward a manifold
of self-organized structures with different shapes and similar energies. These
structures are studied in terms of a phase diagram in density and the
corresponding sensitivity to the isospin-dependent part of the equation of
state and to the isotopic composition is investigated.Comment: 8 pages, 5 figures, conference NN201
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