1,236 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
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
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
Where do winds come from? A new theory on how water vapor condensation influences atmospheric pressure and dynamics
Phase transitions of atmospheric water play a ubiquitous role in the Earth's
climate system, but their direct impact on atmospheric dynamics has escaped
wide attention. Here we examine and advance a theory as to how condensation
influences atmospheric pressure through the mass removal of water from the gas
phase with a simultaneous account of the latent heat release. Building from the
fundamental physical principles we show that condensation is associated with a
decline in air pressure in the lower atmosphere. This decline occurs up to a
certain height, which ranges from 3 to 4 km for surface temperatures from 10 to
30 deg C. We then estimate the horizontal pressure differences associated with
water vapor condensation and find that these are comparable in magnitude with
the pressure differences driving observed circulation patterns. The water vapor
delivered to the atmosphere via evaporation represents a store of potential
energy available to accelerate air and thus drive winds. Our estimates suggest
that the global mean power at which this potential energy is released by
condensation is around one per cent of the global solar power -- this is
similar to the known stationary dissipative power of general atmospheric
circulation. We conclude that condensation and evaporation merit attention as
major, if previously overlooked, factors in driving atmospheric dynamics
Greenhouse effect dependence on atmospheric concentrations of greenhouse substances and the nature of climate stability on Earth
International audienceDue to the exponential positive feedback between sea surface temperature and saturated water vapour concentration, dependence of the planetary greenhouse effect on atmospheric water content is critical for stability of a climate with extensive liquid hydrosphere. In this paper on the basis of the law of energy conservation we develop a simple physically transparent approach to description of radiative transfer in an atmosphere containing greenhouse substances. It is shown that the analytical solution of the equation thus derived coincides with the exact solution of the well-known radiative transfer equation to the accuracy of 20% for all values of atmospheric optical depth. The derived equation makes it possible to easily take into account the non-radiative thermal fluxes (convection and latent heat) and obtain an analytical dependence of the greenhouse effect on atmospheric concentrations of a set of greenhouse substances with arbitrary absorption intervals. The established dependence is used to analyse stability of the modern climate of Earth. It is shown that the modern value of global mean surface temperature, which corresponds to the liquid state of the terrestrial hydrosphere, is physically unstable. The observed stability of modern climate over geological timescales is therefore likely to be due to dynamic singularities in the physical temperature-dependent behaviour of the greenhouse effect. We hypothesise that such singularities may appear due to controlling functioning of the natural global biota and discuss major arguments in support of this conclusion
Biotic pump of atmospheric moisture as driver of the hydrological cycle on land
In this paper the basic geophysical and ecological principles are jointly analyzed that allow the landmasses of Earth to remain moistened sufficiently for terrestrial life to be possible. 1. Under gravity, land inevitably loses water to the ocean. To keep land moistened, the gravitational water runoff must be continuously compensated by the atmospheric ocean-to-land moisture transport. Using data for five terrestrial transects of the International Geosphere Biosphere Program we show that the mean distance to which air fluxes can transport moisture over non-forested areas, does not exceed several hundred kilometers; precipitation decreases exponentially with distance from the ocean. 2. In contrast, precipitation over extensive natural forests does not depend on the distance from the ocean along several thousand kilometers, as illustrated for the Amazon and Yenisey river basins and Equatorial Africa. This points to the existence of an active biotic pump transporting atmospheric moisture inland from the ocean. 3. Physical principles of the biotic moisture pump are investigated based on the previously unstudied properties of atmospheric water vapor, which can be either in or out of aerostatic equilibrium depending on the lapse rate of air temperature. A novel physical principle is formulated according to which the low-level air moves from areas with weak evaporation to areas with more intensive evaporation. Due to the high leaf area index, natural forests maintain high evaporation fluxes, which support the ascending air motion over the forest and "suck in" moist air from the ocean, which is the essence of the biotic pump of atmospheric moisture. In the result, the gravitational runoff water losses from the optimally moistened forest soil can be fully compensated by the biotically enhanced precipitation at any distance from the ocean. 4. It is discussed how a continent-scale biotic water pump mechanism could be produced by natural selection acting on individual trees. 5. Replacement of the natural forest cover by a low leaf index vegetation leads to an up to tenfold reduction in the mean continental precipitation and runoff, in contrast to the previously available estimates made without accounting for the biotic moisture pump. The analyzed body of evidence testifies that the long-term stability of an intense terrestrial water cycle is unachievable without the recovery of natural, self-sustaining forests on continent-wide areas
Photon storage in Lambda-type optically dense atomic media. II. Free-space model
In a recent paper [Gorshkov et al., Phys. Rev. Lett. 98, 123601 (2007)], we
presented a universal physical picture for describing a wide range of
techniques for storage and retrieval of photon wave packets in Lambda-type
atomic media in free space, including the adiabatic reduction of the photon
group velocity, pulse-propagation control via off-resonant Raman techniques,
and photon-echo based techniques. This universal picture produced an optimal
control strategy for photon storage and retrieval applicable to all approaches
and yielded identical maximum efficiencies for all of them. In the present
paper, we present the full details of this analysis as well some of its
extensions, including the discussion of the effects of non-degeneracy of the
two lower levels of the Lambda system. The analysis in the present paper is
based on the intuition obtained from the study of photon storage in the cavity
model in the preceding paper [Gorshkov et al., Phys. Rev. A 76, 033804 (2007)].Comment: 26 pages, 8 figures. V2: significant changes in presentation, new
references, higher resolution of 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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