1,743 research outputs found
Dissipative heat engine is thermodynamically inconsistent
A heat engine operating on the basis of the Carnot cycle is considered, where
the mechanical work performed is dissipated within the engine at the
temperature of the warmer isotherm and the resulting heat is added to the
engine together with an external heat input. The resulting work performed by
the engine per cycle is increased at the expense of dissipated work produced in
the previous cycle. It is shown that such a dissipative heat engine is
thermodynamically inconsistent violating the first and second laws of
thermodynamics. The existing physical models employing the dissipative heat
engine concept, in particular, the heat engine model of hurricane development,
are physically invalid.Comment: 9 pages, 2 figure
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
We numerically examine the spatial evolution of the structure of coherent and
partially coherent laser beams (PCBs), including the optical vortices,
propagating in turbulent atmospheres. The influence of beam fragmentation and
wandering relative to the axis of propagation (z-axis) on the value of the
scintillation index (SI) of the signal at the detector is analyzed. A method
for significantly reducing the SI, by averaging the signal at the detector over
a set of PCBs, is described. This novel method is to generate the PCBs by
combining two laser beams - Gaussian and vortex beams, with different
frequencies (the difference between these two frequencies being significantly
smaller than the frequencies themselves). In this case, the SI is effectively
suppressed without any high-frequency modulators.Comment: 13 pages, 8 figure
Constraints on short-range spin-dependent interactions from scalar spin-spin coupling in deuterated molecular hydrogen
A comparison between existing measurements and calculations of the scalar
spin-spin interaction (J-coupling) in deuterated molecular hydrogen (HD) yields
stringent constraints on anomalous spin-dependent potentials between nucleons
at the atomic scale (). The dimensionless coupling constant
associated with exchange of pseudoscalar (axion-like)
bosons between nucleons is constrained to be less than for
boson masses in the range of . This represents improvement by a
factor of about 100 over constraints placed by measurements of the
dipole-dipole interaction in molecular . The dimensionless coupling
constant associated with exchange of a heretofore
undiscovered axial-vector boson between nucleons is constrained to be
for bosons of mass , improving constraints at this distance scale by a factor of 100 for
proton-proton couplings and more than 8 orders of magnitude for neutron-proton
couplings. This limit is also a factor of 100 more stringent than recent
constraints obtained for axial-vector couplings between electrons and nucleons
obtained from comparison of measurements and calculations of hyperfine
structure.Comment: 4 pages 2 figure
Light storage in an optically thick atomic ensemble under conditions of electromagnetically induced transparency and four-wave mixing
We study the modification of a traditional electromagnetically induced
transparency (EIT) stored light technique that includes both EIT and four-wave
mixing (FWM) in an ensemble of hot Rb atoms. The standard treatment of light
storage involves the coherent and reversible mapping of one photonic mode onto
a collective spin coherence. It has been shown that unwanted, competing
processes such as four-wave mixing are enhanced by EIT and can significantly
modify the signal optical pulse propagation. We present theoretical and
experimental evidence to indicate that while a Stokes field is indeed detected
upon retrieval of the signal field, any information originally encoded in a
seeded Stokes field is not independently preserved during the storage process.
We present a simple model that describes the propagation dynamics of the fields
and the impact of FWM on the spin wave.Comment: 13 pages, 10 figure
Scaling the neutral atom Rydberg gate quantum computer by collective encoding in Holmium atoms
We discuss a method for scaling a neutral atom Rydberg gate quantum processor
to a large number of qubits. Limits are derived showing that the number of
qubits that can be directly connected by entangling gates with errors at the
level using long range Rydberg interactions between sites in an
optical lattice, without mechanical motion or swap chains, is about 500 in two
dimensions and 7500 in three dimensions. A scaling factor of 60 at a smaller
number of sites can be obtained using collective register encoding in the
hyperfine ground states of the rare earth atom Holmium. We present a detailed
analysis of operation of the 60 qubit register in Holmium. Combining a lattice
of multi-qubit ensembles with collective encoding results in a feasible design
for a 1000 qubit fully connected quantum processor.Comment: 6 figure
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