180,114 research outputs found
A Lattice Model of Intercalation
The thermodynamics of the lattice model of intercalation of ions in crystals
is considered in the mean field approximation. Pseudospin formalism is used for
the description of interaction of electrons with ions and the possibility of
hopping of intercalated ions between different positions is taken into account.
Phase diagrams are built. It is shown that the effective interaction between
intercalated ions can lead to phase separation or to appearance of modulated
phase (it depends on filling of the electron energy band). At high values of
the parameter of ion transfer the ionic subsystem can pass to the
superfluid-like state
Three-body rf association of Efimov trimers
We present a theoretical analysis of rf association of Efimov trimers in a
2-component Bose gas with short-range interactions. Using the adiabatic
hyperspherical Green's function formalism to solve the quantum 3-body problem,
we obtain universal expressions for 3-body rf association rates as a function
of the s-wave scattering length . We find that the association rates scale
as in the limit of large , and diverge as whenever
an Efimov state crosses the atom-dimer threshold (where stands for the
atom-dimer scattering length). Our calculations show that trimer formation
rates as large as cm/s can be achieved with rf Rabi
frequencies of order 1 MHz, suggesting that direct rf association is a powerful
tool of making and probing few-body quantum states in ultracold atomic gases.Comment: 4 pages, 2 figure
Semiconductor cavity QED: Bandgap induced by vacuum fluctuations
We consider theoretically a semiconductor nanostructure embedded in
one-dimensional microcavity and study the modification of its electron energy
spectrum by the vacuum fluctuations of the electromagnetic field. To solve the
problem, a non-perturbative diagrammatic approach based on the Green's function
formalism is developed. It is shown that the interaction of the system with the
vacuum fluctuations of the optical cavity opens gaps within the valence band of
the semiconductor. The approach is verified for the case of large photon
occupation numbers, proving the validity of the model by comparing to previous
studies of the semiconductor system excited by a classical electromagnetic
field. The developed theory is of general character and allows for unification
of quantum and classical descriptions of the strong light-matter interaction in
semiconductor structures
Control of a single-particle localization in open quantum systems
We investigate the possibility to control localization properties of the
asymptotic state of an open quantum system with a tunable synthetic
dissipation. The control mechanism relies on the matching between properties of
dissipative operators, acting on neighboring sites and specified by a single
control parameter, and the spatial phase structure of eigenstates of the system
Hamiltonian. As a result, the latter coincide (or near coincide) with the dark
states of the operators. In a disorder-free Hamiltonian with a flat band, one
can either obtain a localized asymptotic state or populate whole flat and/or
dispersive bands, depending on the value of the control parameter. In a
disordered Anderson system, the asymptotic state can be localized anywhere in
the spectrum of the Hamiltonian. The dissipative control is robust with respect
to an additional local dephasing.Comment: 6 pages, 5 figure
Localization in open quantum systems
In an isolated single-particle quantum system a spatial disorder can induce
Anderson localization. Being a result of interference, this phenomenon is
expected to be fragile in the face of dissipation. Here we show that
dissipation can drive a disordered system into a steady state with tunable
localization properties. This can be achieved with a set of identical
dissipative operators, each one acting non-trivially only on a pair of
neighboring sites. Operators are parametrized by a uniform phase, which
controls selection of Anderson modes contributing to the state. On the
microscopic level, quantum trajectories of a system in a localized steady
regime exhibit intermittent dynamics consisting of long-time sticking events
near selected modes interrupted by jumps between them.Comment: 5 pages, 5 figure
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