49,711 research outputs found
The Universality and stability for a dilute Bose gas with a Feshbach resonance
We study the bosonic atoms with a wide Feshbach resonance at zero temperature
in terms of the renormalization group. We indicate that this system will always
collapse in the dilute limit. On the side with a positive scattering length,
the atomic superfluid is an unstable local minimum in the dilute limit and it
determines the thermodynamics of this system within its lifetime. We calculate
the equilibrium properties at zero temperature in the unitary regime. They
exhibit universal scaling forms in the dilute limit due to the presence of a
nontrivial zero temperature, zero density fixed point. Moreover, we find that
the T=0 thermodynamics of this system in the unitary limit is exactly identical
to the one for an ideal Fermi gas.Comment: 6 pages, 4 figure
Average quantum dynamics of closed systems over stochastic Hamiltonians
We develop a master equation formalism to describe the evolution of the
average density matrix of a closed quantum system driven by a stochastic
Hamiltonian. The average over random processes generally results in decoherence
effects in closed system dynamics, in addition to the usual unitary evolution.
We then show that, for an important class of problems in which the Hamiltonian
is proportional to a Gaussian random process, the 2nd-order master equation
yields exact dynamics. The general formalism is applied to study the examples
of a two-level system, two atoms in a stochastic magnetic field and the heating
of a trapped ion.Comment: 17 pages, 1 figure, submitted to Physical Review
Localizable invariants of combinatorial manifolds and Euler characteristic
It is shown that if a real value PL-invariant of closed combinatorial
manifolds admits a local formula that depends only on the f-vector of the link
of each vertex, then the invariant must be a constant times the Euler
characteristic.Comment: 14 pages, 5 figures. Some arguments are improved and one picture is
adde
Nonequilibrium noise correlations in a point contact of helical edge states
We investigate theoretically the nonequilibrium finite-frequency current
noise in a four-terminal quantum point contact of interacting helical edge
states at a finite bias voltage. Special focus is put on the effects of the
single-particle and two-particle scattering between the two helical edge states
on the fractional charge quasiparticle excitations shown in the nonequilibrium
current noise spectra. Via the Keldysh perturbative approach, we find that the
effects of the single-particle and the two-particle scattering processes on the
current noise depend sensitively on the Luttinger liquid parameter. Moreover,
the Fano factors for the auto- and cross correlations of the currents in the
terminals are distinct from the ones for tunneling between the chiral edge
states in the quantum Hall liquid. The current noise spectra in the
single-particle-scattering-dominated and the two-particle-scattering-dominated
regime are shown. Experimental implications of our results on the transport
through the helical edges in two-dimensional topological insulators are
discussed.Comment: 10 pages, 8 figure
The Photonic Band theory and the negative refraction experiment of metallic helix metamaterials
We develop a theory to compute and interpret the photonic band structure of a
periodic array of metallic helices for the first time. Interesting features of
band structure include the ingenuous longitudinal and circularly polarized
eigenmodes, the wide polarization gap [Science 325, 1513 (2009)], and the
helical symmetry guarantees the existence of negative group velocity bands at
both sides of the polarization gap and band crossings pinned at the zone
boundary with fixed frequencies. A direct proof of negative refraction via a
chiral route [Science 306, 1353 (2004)] is achieved for the first time by
measuring Gooshanchen shift through a slab of three dimensional bona fide helix
metamaterial
Nonexistence of Entanglement Sudden Death in High NOON States
We study the dynamics of entanglement in continuous variable quantum systems
(CVQS). Specifically, we study the phenomena of Entanglement Sudden Death (ESD)
in general two-mode-N-photon states undergoing pure dephasing. We show that for
these states, ESD never occurs. These states are generalizations of the
so-called High NOON states, shown to decrease the Rayleigh limit of lambda to
lambda/N, which promises great improvement in resolution of interference
patterns if states with large N are physically realized. However, we show that
in dephasing NOON states, the time to reach V_crit, critical visibility, scales
inversely with N^2. On the practical level, this shows that as N increases, the
visibility degrades much faster, which is likely to be a considerable drawback
for any practical application of these states.Comment: 4 pages, 1 figur
Hamiltonian approach to the bound state problem in QCD_2
Bosonization of the two-dimensional QCD in the large N_C limit is performed
in the framework of Hamiltonian approach in the Coulomb gauge. The generalized
Bogoliubov transformation is applied to diagonalize the Hamiltonian in the
bosonic sector of the theory, and the composite operators creating/annihilating
bosons are obtained in terms of dressed quark operators. The bound state
equation is reconstructed as a result of the generalized Bogoliubov
transformation, and the form of its massless solution, chiral pion, is found
explicitly. Chiral properties of the theory are discussed.Comment: 9 pages, LaTeX2
Mechanism for graphene-based optoelectronic switches by tuning surface plasmon-polaritons in monolayer graphene
It is shown that one can explore the optical conductivity of graphene,
together with the ability of controlling its electronic density by an applied
gate voltage, in order to achieve resonant coupling between an external
electromagnetic radiation and surface plasmon-polaritons in the graphene layer.
This opens the possibility of electrical control of the intensity of light
reflected inside a prism placed on top of the graphene layer, by switching
between the regimes of total reflection and total absorption. The predicted
effect can be used to build graphene-based opto-electronic switches.Comment: 5 page
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