822 research outputs found
Condensate deformation and quantum depletion of Bose-Einstein condensates in external potentials
The one-body density matrix of weakly interacting, condensed bosons in
external potentials is calculated using inhomogeneous Bogoliubov theory. We
determine the condensate deformation caused by weak external potentials on the
mean-field level. The momentum distribution of quantum fluctuations around the
deformed ground state is obtained analytically, and finally the resulting
quantum depletion is calculated. The depletion due to the external potential,
or potential depletion for short, is a small correction to the homogeneous
depletion, validating our inhomogeneous Bogoliubov theory. Analytical results
are derived for weak lattices and spatially correlated random potentials, with
simple, universal results in the Thomas-Fermi limit of very smooth potentials.Comment: 17 pages, 4 figures. v2: published version, minor change
Spin-dependent THz oscillator based on hybrid graphene superlattices
We theoretically study the occurrence of Bloch oscillations in biased hybrid
graphene systems with spin-dependent superlattices. The spin-dependent
potential is realized by a set of ferromagnetic insulator strips deposited on
top of a gapped graphene nanoribbon, which induce a proximity exchange
splitting of the electronic states in the graphene monolayer. We numerically
solve the Dirac equation and study Bloch oscillations in the lowest conduction
band of the spin-dependent superlattice. While the Bloch frequency is the same
for both spins, we find the Bloch amplitude to be spin dependent. This
difference results in a spin-polarized ac electric current in the THz range.Comment: 4 pages, 6 figure
On the Universality of the Entropy-Area Relation
We present an argument that, for a large class of possible dynamics, a
canonical quantization of gravity will satisfy the Bekenstein-Hawking
entropy-area relation. This result holds for temperatures low compared to the
Planck temperature and for boundaries with areas large compared to Planck area.
We also relate our description, in terms of a grand canonical ensemble, to
previous geometric entropy calculations using area ensembles.Comment: 6 page
Regularized Hamiltonians and Spinfoams
We review a recent proposal for the regularization of the scalar constraint
of General Relativity in the context of LQG. The resulting constraint presents
strengths and weaknesses compared to Thiemann's prescription. The main
improvement is that it can generate the 1-4 Pachner moves and its matrix
elements contain 15j Wigner symbols, it is therefore compatible with the
spinfoam formalism: the drawback is that Thiemann anomaly free proof is spoiled
because the nodes that the constraint creates have volume.Comment: 4 pages, based on a talk given at Loops '11 in Madrid, to appear in
Journal of Physics: Conference Series (JPCS
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