1,474 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
On the forward-backward charge asymmetry in e+e- -annihilation into hadrons at high energies
The forward-backward asymmetry in e+ e- annihilation into a quark-antiquark
pair is considered in the double-logarithmic approximation at energies much
higher than the masses of the weak bosons. It is shown that after accounting to
all orders for the exchange of virtual photons and W, Z -bosons one is lead to
the following effect (asymmetry): quarks with positive electric charge (e.g. u,
\bar{d}) tend to move in the e+ - direction whereas quarks with negative
charges (e.g. d, \bar{u}) tend to move in the e- - direction. The value of the
asymmetry grows with increasing energy when the produced quarks are within a
cone with opening angle, in the cmf, \theta_0\sim 2M_Z/\sqrt{s} around the e+e-
-beam. Outside this cone, at \theta_0 << \theta << 1, the asymmetry is
inversely proportional to \theta .Comment: 17 Pages, 2 Tables, 4 Figures. Hadronization effects to the asymmetry
are considered with more detail
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
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
Beyond the Spin Model Approximation for Ramsey Spectroscopy
Ramsey spectroscopy has become a powerful technique for probing
non-equilibrium dynamics of internal (pseudospin) degrees of freedom of
interacting systems. In many theoretical treatments, the key to understanding
the dynamics has been to assume the external (motional) degrees of freedom are
decoupled from the pseudospin degrees of freedom. Determining the validity of
this approximation -- known as the spin model approximation -- is complicated,
and has not been addressed in detail. Here we shed light in this direction by
calculating Ramsey dynamics exactly for two interacting spin-1/2 particles in a
harmonic trap. We focus on -wave-interacting fermions in quasi-one and
two-dimensional geometries. We find that in 1D the spin model assumption works
well over a wide range of experimentally-relevant conditions, but can fail at
time scales longer than those set by the mean interaction energy. Surprisingly,
in 2D a modified version of the spin model is exact to first order in the
interaction strength. This analysis is important for a correct interpretation
of Ramsey spectroscopy and has broad applications ranging from precision
measurements to quantum information and to fundamental probes of many-body
systems
Spin Diffusion and Relaxation in a Nonuniform Magnetic Field
We consider a quasiclassical model that allows us to simulate the process of
spin diffusion and relaxation in the presence of a highly nonuniform magnetic
field. The energy of the slow relaxing spins flows to the fast relaxing spins
due to the dipole-dipole interaction between the spins. The magnetic field
gradient suppresses spin diffusion and increases the overall relaxation time in
the system. The results of our numerical simulations are in a good agreement
with the available experimental data.Comment: 11 pages and 6 figure
Interacting Qubit-Photon Bound States with Superconducting Circuits
Qubits strongly coupled to a photonic crystal give rise to many exotic
physical scenarios, beginning with single and multi-excitation qubit-photon
dressed bound states comprising induced spatially localized photonic modes,
centered around the qubits, and the qubits themselves. The localization of
these states changes with qubit detuning from the band-edge, offering an avenue
of in situ control of bound state interaction. Here, we present experimental
results from a device with two qubits coupled to a superconducting microwave
photonic crystal and realize tunable on-site and inter-bound state
interactions. We observe a fourth-order two photon virtual process between
bound states indicating strong coupling between the photonic crystal and
qubits. Due to their localization-dependent interaction, these states offer the
ability to create one-dimensional chains of bound states with tunable and
potentially long-range interactions that preserve the qubits' spatial
organization, a key criterion for realization of certain quantum many-body
models. The widely tunable, strong and robust interactions demonstrated with
this system are promising benchmarks towards realizing larger, more complex
systems of bound states
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