66 research outputs found
Oscillatory and non-oscillatory criteria for linear four-dimensional Hamiltonian systems
summary:The Riccati equation method is used to study the oscillatory and non-oscillatory behavior of solutions of linear four-dimensional Hamiltonian systems. One oscillatory and three non-oscillatory criteria are proved. Examples of the obtained results are compared with some well known ones
Correlation-induced localization
A new paradigm of Anderson localization caused by correlations in the
long-range hopping along with uncorrelated on-site disorder is considered which
requires a more precise formulation of the basic localization-delocalization
principles. A new class of random Hamiltonians with translation-invariant
hopping integrals is suggested and the localization properties of such models
are established both in the coordinate and in the momentum spaces alongside
with the corresponding level statistics. Duality of translation-invariant
models in the momentum and coordinate space is uncovered and exploited to find
a full localization-delocalization phase diagram for such models. The crucial
role of the spectral properties of hopping matrix is established and a new
matrix inversion trick is suggested to generate a one-parameter family of
equivalent localization/delocalization problems. Optimization over the free
parameter in such a transformation together with the
localization/delocalization principles allows to establish exact bounds for the
localized and ergodic states in long-range hopping models. When applied to the
random matrix models with deterministic power-law hopping this transformation
allows to confirm localization of states at all values of the exponent in
power-law hopping and to prove analytically the symmetry of the exponent in the
power-law localized wave functions.Comment: 14 pages, 8 figures + 5 pages, 2 figures in appendice
Collective coherence in planar semiconductor microcavities
Semiconductor microcavities, in which strong coupling of excitons to confined
photon modes leads to the formation of exciton-polariton modes, have
increasingly become a focus for the study of spontaneous coherence, lasing, and
condensation in solid state systems. This review discusses the significant
experimental progress to date, the phenomena associated with coherence which
have been observed, and also discusses in some detail the different theoretical
models that have been used to study such systems. We consider both the case of
non-resonant pumping, in which coherence may spontaneously arise, and the
related topics of resonant pumping, and the optical parametric oscillator.Comment: 46 pages, 12 figure
The role of fluctuations in quantum and classical time crystals
Discrete time crystals (DTCs) are a many-body state of matter whose dynamics
are slower than the forces acting on it. The same is true for classical systems
with period-doubling bifurcations. Hence, the question naturally arises what
differentiates classical from quantum DTCs. Here, we analyze a variant of the
Bose-Hubbard model, which describes a plethora of physical phenomena and has
both a classical and a quantum time-crystalline limit. We study the role of
fluctuations on the stability of the system and find no distinction between
quantum and classical DTCs. This allows us to probe the fluctuations in an
experiment using two strongly coupled parametric resonators subject to
classical noise.Comment: 11 pages, 5 figure
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