5,151 research outputs found
Bose-Hubbard model with attractive interactions
We consider the Bose-Hubbard model of atoms in an optical lattice potential
when the atom-atom interactions are attractive. If the lowest energy lattice
sites are degenerate (such as in the homogeneous case), then, at a critical
value of the interaction strength, a phase-coherent condensate becomes unstable
to a quantum superposition such that the number distribution of each of the
degenerate sites becomes double peaked. In the limit when the interaction
dominates, the superposition becomes macroscopic and has the form
, where
is the total number of atoms and the sum ranges over the energy-degenerate
sites.Comment: 4 pager, 5 figures, accepted for publication in PR
Maximal entanglement of two spinor Bose-Einstein condensates
Starting with two weakly-coupled anti-ferromagnetic spinor condensates, we
show that by changing the sign of the coefficient of the spin interaction,
, via an optically-induced Feshbach resonance one can create an
entangled state consisting of two anti-correlated ferromagnetic condensates.
This state is maximally entangled and a generalization of the Bell state from
two anti-correlated spin-1/2 particles to two anti-correlated spin atomic
samples, where is the total number of atoms.Comment: 5 pages, 3 figures, accepted for publication in PR
On-demand single-photon state generation via nonlinear absorption
We propose a method for producing on-demand single-photon states based on
collision-induced exchanges of photons and unbalanced linear absorption between
two single-mode light fields. These two effects result in an effective
nonlinear absorption of photons in one of the modes, which can lead to single
photon states. A quantum nonlinear attenuator based on such a mechanism can
absorb photons in a normal input light pulse and terminate the absorption at a
single-photon state. Because the output light pulses containing single photons
preserve the properties of the input pulses, we expect this method to be a
means for building a highly controllable single photon source.Comment: 5 pages, 2 figures, to appear in PRA. To be published in PR
Tax evasion and exchange equity: a reference-dependent approach
The standard portfolio model of tax evasion with a public good produces the perverse conclusion that when taxpayers perceive the public good to be under-/overprovided, an increase in the tax rate increases/decreases evasion. The author treats taxpayers as thinking in terms of gains and losses relative to an endogenous reference level, which reflects perceived exchange equity between the value of taxes paid and the value of public goods supplied. With these alternative behavioral assumptions, the author overturns the aforementioned result in a direction consistent with the empirical evidence. The author also finds a role for relative income in determining individual responses to a change in the marginal rate of tax
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