8,598 research outputs found
Generalized Second-Order Thomas-Fermi Method for Superfluid Fermi Systems
Using the -expansion of the Green's function of the
Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi
approximation to generalized superfluid Fermi systems by including the
density-dependent effective mass and the spin-orbit potential. We first
implement and examine the full correction terms over different energy intervals
of the quasiparticle spectra in calculations of finite nuclei. Final
applications of this generalized Thomas-Fermi method are intended for various
inhomogeneous superfluid Fermi systems.Comment: 8 pages, 10 figures, PR
Controlling Excitations Inversion of a Cooper Pair Box Interacting with a Nanomechanical Resonator
We investigate the action of time dependent detunings upon the excitation
inversion of a Cooper pair box interacting with a nanomechanical resonator. The
method employs the Jaynes-Cummings model with damping, assuming different decay
rates of the Cooper pair box and various fixed and t-dependent detunings. It is
shown that while the presence of damping plus constant detunings destroy the
collapse/revival effects, convenient choices of time dependent detunings allow
one to reconstruct such events in a perfect way. It is also shown that the mean
excitation of the nanomechanical resonator is more robust against damping of
the Cooper pair box for convenient values of t-dependent detunings.Comment: 11 pages, 5 figure
Fermi-Bose Mixtures Near Broad Interspecies Feshbach Resonances
In this Letter we have studied dressed bound states in Fermi-Bose mixtures
near broad interspecies resonance, and implications on many-body correlations.
We present the evidence for a first order phase transition between a mixture of
Fermi gas and condensate, and a fully paired mixture where extended fermionic
molecules occupy a single pairing channel instead of forming a molecular Fermi
surface. We have further investigated the effect of Fermi surface dynamics,
pair fluctuations and discussed the validity of our results.Comment: 5 pages, 4 figure
Quantum ratchet transport with minimal dispersion rate
We analyze the performance of quantum ratchets by considering the dynamics of
an initially localized wave packet loaded into a flashing periodic potential.
The directed center-of-mass motion can be initiated by the uniform modulation
of the potential height, provided that the modulation protocol breaks all
relevant time- and spatial reflection symmetries. A poor performance of quantum
ratchet transport is characterized by a slow net motion and a fast diffusive
spreading of the wave packet, while the desirable optimal performance is the
contrary. By invoking a quantum analog of the classical P\'eclet number, namely
the quotient of the group velocity and the dispersion of the propagating wave
packet, we calibrate the transport properties of flashing quantum ratchets and
discuss the mechanisms that yield low-dispersive directed transport.Comment: 6 pages; 3 figures; 1 tabl
The Apparently Decaying Orbit of WASP-12
We present new transit and occultation times for the hot Jupiter WASP-12b.
The data are compatible with a constant period derivative:
ms yr and Myr. However, it is difficult to tell whether
we have observed orbital decay, or a portion of a 14-year apsidal precession
cycle. If interpreted as decay, the star's tidal quality parameter is
about . If interpreted as precession, the planet's Love number is
. Orbital decay appears to be the more parsimonious model: it is
favored by despite having two fewer free parameters than the
precession model. The decay model implies that WASP-12 was discovered within
the final 0.2% of its existence, which is an unlikely coincidence but
harmonizes with independent evidence that the planet is nearing disruption.
Precession does not invoke any temporal coincidence, but does require some
mechanism to maintain an eccentricity of 0.002 in the face of rapid
tidal circularization. To distinguish unequivocally between decay and
precession will probably require a few more years of monitoring. Particularly
helpful will be occultation timing in 2019 and thereafter.Comment: 10 pages [AAS journals, in press, note added in proof
Anomalous Dimers in Quantum Mixtures near Broad Resonances: Pauli Blocking, Fermi Surface Dynamics and Implications
We study the energetics and dispersion of anomalous dimers that are induced
by the Pauli blocking effect in a quantum Fermi gas of majority atoms near
interspecies resonances. Unlike in vacuum, we find that both the sign and
magnitude of the dimer masses are tunable via Feshbach resonances. We also
investigate the effects of particle-hole fluctuations on the dispersion of
dimers and demonstrate that the particle-hole fluctuations near a Fermi surface
(with Fermi momentum ) generally reduce the effective two-body
interactions and the binding energy of dimers. Furthermore, in the limit of
light minority atoms the particle-hole fluctuations disfavor the formation of
dimers with a total momentum , because near the modes
where the dominating particle-hole fluctuations appear are the softest. Our
calculation suggests that near broad interspecies resonances when the
minority-majority mass ratio is smaller than a critical value
(estimated to be 0.136), dimers in a finite-momentum channel are energetically
favored over dimers in the zero-momentum channel. We apply our theory to
quantum gases of LiK, LiRb, KRb and
LiNa near broad interspecies resonances, and discuss the
limitations of our calculations and implications.Comment: 15 pages, 10 figures, published versio
Superluminal group velocity in an anisotropic metamaterial
Based on boundary condition and dispersion relation, the superluminal group
velocity in an anisotropic metamaterial (AMM) is investigated. The superluminal
propagation is induced by the hyperbolic dispersion relation associated with
the AMM. It is shown that a modulated Gaussian beam exhibits a superluminal
group velocity which depends on the choice of incident angles and optical axis
angles. The superluminal propagation does not violate the theory of special
relativity because the group velocity is the velocity of the peak of the
localized wave packet which does not carry information. It is proposed that a
triglycine sulfate (TGS) crystal can be designed and the superluminal group
velocity can be measured experimentally.Comment: 9 pages, 3 figure
Cryptanalysis of the Hillery-Buzek-Berthiaume quantum secret-sharing protocol
The participant attack is the most serious threat for quantum secret-sharing
protocols. We present a method to analyze the security of quantum
secret-sharing protocols against this kind of attack taking the scheme of
Hillery, Buzek, and Berthiaume (HBB) [Phys. Rev. A 59 1829 (1999)] as an
example. By distinguishing between two mixed states, we derive the necessary
and sufficient conditions under which a dishonest participant can attain all
the information without introducing any error, which shows that the HBB
protocol is insecure against dishonest participants. It is easy to verify that
the attack scheme of Karlsson, Koashi, and Imoto [Phys. Rev. A 59, 162 (1999)]
is a special example of our results. To demonstrate our results further, we
construct an explicit attack scheme according to the necessary and sufficient
conditions. Our work completes the security analysis of the HBB protocol, and
the method presented may be useful for the analysis of other similar protocols.Comment: Revtex, 7 pages, 3 figures; Introduction modifie
Construction of a polarization insensitive lens from a quasi-isotropic metamaterial slab
We propose to employ the quasiisotropic metamaterial (QIMM) slab to construct
a polarization insensitive lens, in which both E- and H-polarized waves exhibit
the same refocusing effect. For shallow incident angles, the QIMM slab will
provide some degree of refocusing in the same manner as an isotropic negative
index material. The refocusing effect allows us to introduce the ideas of
paraxial beam focusing and phase compensation by the QIMM slab. On the basis of
angular spectrum representation, a formalism describing paraxial beams
propagating through a QIMM slab is presented. Because of the negative phase
velocity in the QIMM slab, the inverse Gouy phase shift and the negative
Rayleigh length of paraxial Gaussian beam are proposed. We find that the phase
difference caused by the Gouy phase shift in vacuum can be compensated by that
caused by the inverse Gouy phase shift in the QIMM slab. If certain matching
conditions are satisfied, the intensity and phase distributions at object plane
can be completely reconstructed at image plane. Our simulation results show
that the superlensing effect with subwavelength image resolution could be
achieved in the form of a QIMM slab.Comment: 25 pages, 8 figure
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