32,786 research outputs found
Secular Effects of Tidal Damping in Compact Planetary Systems
We describe the long-term evolution of compact systems of terrestrial
planets, using a set of simulations that match the statistical properties of
the observed exoplanet distribution. The evolution is driven by tidal
dissipation in the planetary interiors, but the systems evolve as a whole due
to secular gravitational interactions. We find that, for Earth-like dissipation
levels, planetary orbits can be circularised out to periods of order 100 days,
an order of magnitude larger than is possible for single planets. The resulting
distribution of eccentricities is a qualitative match to that inferred from
transit timing variations, with a minority of non-zero eccentricities
maintained by particular secular configurations. The coupling of the tidal and
secular processes enhance the inward migration of the innermost planets in
these systems, and can drive them to short orbital periods. Resonant
interactions of both the mean motion and secular variety are observed, although
the interactions are not strong enough to drive systemic instability in most
cases. However, we demonstrate that these systems can easily be driven unstable
if coupled to giant planets on longer period orbits.Comment: 17 pages, 22 figures, 2 tables, submitted to Monthly Notices of the
Royal Astronomical Societ
Bright bichromatic entanglement and quantum dynamics of sum frequency generation
We investigate the quantum properties of the well-known process of sum
frequency generation, showing that it is potentially a very useful source of
non-classical states of the electromagnetic field, some of which are not
possible with the more common techniques. We show that it can produce
quadrature squeezed light, bright bichromatic entangled states and symmetric
and asymmetric demonstrations of the Einstein-Podolsky-Rosen paradox. We also
show that the semiclassical equations totally fail to describe the mean-field
dynamics when the cavity is strongly pumped
Quantum ultra-cold atomtronics
It is known that a semi-classical analysis is not always adequate for
atomtronics devices, but that a fully quantum analysis is often necessary to
make reliable predictions. While small numbers of atoms at a small number of
sites are tractable using the density matrix, a fully quantum analysis is often
not straightforward as the system becomes larger. We show that the fully
quantum positive-P representation is then a viable calculational tool. We
postulate an atomtronic phase-gate consisting of four wells in a Bose-Hubbard
configuration, for which the semi-classical dynamics are controllable using the
phase of the atomic mode in one of the wells. We show that the quantum
predictions of the positive-P representation for the performance of this device
have little relation to those found semi-classically, and that the performance
depends markedly on the actual quantum states of the initially occupied modes.
We find that initial coherent states lead to closest to classical dynamics, but
that initial Fock states give results that are quite different. A fully quantum
analysis also opens the door for deeply quantum atomtronics, in which
properties such as entanglement and EPR (Einstein-Podolsky-Rosen) steering
become valuable technical properties of a device.Comment: 12 pages, 6 figures, submitted to Phys. Rev
A quantum correlated twin atom laser from a Bose-Hubbard system
We propose and evaluate a method to construct a quantum correlated twin atom
laser using a pumped and damped Bose-Hubbard inline trimer which can operate in
a stationary regime. With pumping via a source condensate filling the middle
well and damping using either an electron beam or optical means at the two end
wells, we show that bipartite quantum correlations build up between the ends of
the chain, and that these can be measured either in situ or in the outcoupled
beams. While nothing similar to our system has yet been achieved
experimentally, recent advances mean that it should be practically realisable
in the near future.Comment: 15 pages, 8 figures, theory. Typos fixed and material added to
introductio
Accounting for Multiplicity in Calculating Eta Earth
Using the updated exoplanet population parameters of our previous study,
which includes the planetary radius updates from Gaia DR2 and an inferred
multiplicity distribution, we provide a revised calculation.
This is achieved by sampling planets from our derived population model and
determining which planets meet our criterion for habitability. To ensure robust
results, we provide probabilities calculated over a range of upper radius
limits. Our most optimistic criterion for habitability provides an
value of . We also
consider the effects of multiplicity and the number of habitable planets each
system may contain. Our calculation indicates that of GK dwarfs
have more than one planet within their habitable zone. This optimistic
habitability criterion also suggests that of solar-like stars
will harbor 5 or more habitable planets. These tightly packed highly habitable
system should be extremely rare, but still possible. Even with our most
pessimistic criterion we still expect that of solar-like stars
harbor more than one habitable planet.Comment: 7 pages, 1 figure; Accepted for publication in MNRA
Scale invariant thermodynamics of a toroidally trapped Bose gas
We consider a system of bosonic atoms in an axially symmetric harmonic trap
augmented with a two dimensional repulsive Gaussian optical potential. We find
an expression for the grand free energy of the system for configurations
ranging from the harmonic trap to the toroidal regime. For large tori we
identify an accessible regime where the ideal gas thermodynamics of the system
are found to be independent of toroidal radius. This property is a consequence
of an invariant extensive volume of the system that we identify analytically in
the regime where the toroidal potential is radially harmonic. In considering
corrections to the scale invariant transition temperature, we find that the
first order interaction shift is the dominant effect in the thermodynamic
limit, and is also scale invariant. We also consider adiabatic loading from the
harmonic to toroidal trap configuration, which we show to have only a small
effect on the condensate fraction of the ideal gas, indicating that loading
into the scale invariant regime may be experimentally practical.Comment: 10 pages, 3 figures, to appear in Phys. Rev. A, typos corrected,
references added, rewritten to emphasize generalized volume. Results
unchange
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