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 Physics , 2004, DOI: 10.1103/PhysRevLett.93.033602 Abstract: We investigate the effect of slow light propagating in a degenerate atomic Fermi gas. In particular we use slow light with an orbital angular momentum. We present a microscopic theory for the interplay between light and matter and show how the slow light can provide an effective magnetic field acting on the electrically neutral fermions, a direct analogy of the free electron gas in an uniform magnetic field. As an example we illustrate how the corresponding de Haas-van Alphen effect can be seen in a neutral gas of fermions.
 Physics , 2005, DOI: 10.1103/PhysRevA.72.021801 Abstract: The effect of finite control beam on the transverse spatial profile of the slow light propagation in an electromagnetically induced transparency medium is studied. We arrive at a general criterion in terms of eigenequation, and demonstrate the existence of a set of localized, stationary transverse modes for the negative detuning of the probe signal field. Each of these diffraction-free transverse modes has its own characteristic group velocity, smaller than the conventional theoretical result without considering the transverse spatial effect.
 Physics , 2001, DOI: 10.1103/PhysRevA.64.013604 Abstract: We study semi-classical slow light propagation in trapped two level atomic quantum gases. The temperature dependent behaviors of both group velocity and transmissions are compared for low temperature Bose, Fermi, and Boltzman gases within the local density approximation for their spatial density profile.
 Physics , 2011, DOI: 10.1103/PhysRevA.83.063605 Abstract: We consider the two-color photooassociation of a quantum degenerate atomic gas into ground-state diatomic molecules via a molecular dark state. This process can be described in terms of a lambda level scheme that is formally analogous to the situation in electromagnetically-induced transparency (EIT) in atomic systems, and therefore can result in slow light propagation. We show that the group velocity of the light field depends explicitly on whether the atoms are bosons or fermions, as well as on the existence or absence of a pairing gap in the case of fermions, so that the measurement of the group velocity realizes a non-destructive diagnosis of the atomic state and the pairing gap.
 Physics , 2011, DOI: 10.1103/PhysRevB.84.035130 Abstract: Disturbances in gapless quantum many-body models are known to travel an unlimited distance throughout the system. Here, we explore this phenomenon in finite clusters with degenerate ground states. The specific model studied here is the one-dimensional J1-J2 Heisenberg Hamiltonian at and close to the Majumdar-Ghosh point. Both open and periodic boundary conditions are considered. Quenches are performed using a local magnetic field. The degenerate Majumdar-Ghosh ground state allows disturbances which carry quantum entanglement to propagate throughout the system, and thus dephase the entire system within the degenerate subspace. These disturbances can also carry polarization, but not energy, as all energy is stored locally. The local evolution of the part of the system where energy is stored drives the rest of the system through long-range entanglement. We also examine approximations for the ground state of this Hamiltonian in the strong field limit, and study how couplings away from the Majumdar-Ghosh point affect the propagation of disturbances. We find that even in the case of approximate degeneracy, a disturbance can be propagated throughout a finite system.
 中国物理 B , 2010, Abstract: This paper investigates the breaking point between fast- and slow-light in a degenerate two-level atomic system, where fast-light can be converted to slow-light arbitrarily on a single transition line by adjusting the strength of the pumping field. An equivalent incoherent pumping rate is introduced in this simplified theoretical model which exploits the dependence of this feature. The experimental observation is presented as evidence of the breaking point where the injected power is about 0.08~{\rm mW}.
 Physics , 2010, DOI: 10.1103/PhysRevLett.96.175502 Abstract: Statistics and thermally activated dynamics of crack nucleation and propagation in a two-dimensional heterogeneous material containing quenched randomly distributed defects are studied theoretically. Using the generalized Griffith criterion we derive the equation of motion for the crack tip position accounting for dissipation, thermal noise and the random forces arising from the defects. We find that aggregations of defects generating long-range interaction forces (e.g., clouds of dislocations) lead to anomalously slow creep of the crack tip or even to its complete arrest. We demonstrate that heterogeneous materials with frozen defects contain a large number of arrested microcracks and that their fracture toughness is enhanced to the experimentally accessible time scales.
 Physics , 2006, Abstract: We investigate propagation of slow-light solitons in atomic media described by the nonlinear $\Lambda$-model. Under a physical assumption, appropriate to the slow light propagation, we reduce the $\Lambda$-scheme to a simplified nonlinear model, which is also relevant to 2D dilatonic gravity. Exact solutions describing various regimes of stopping slow-light solitons can then be readily derived.
 Physics , 2001, Abstract: Recent theoretical work has shown that so-called pulled fronts propagating into an unstable state always converge very slowly to their asymptotic speed and shape. In the the light of these predictions, we reanalyze earlier experiments by Fineberg and Steinberg on front propagation in a Rayleigh-B\'enard cell. In contrast to the original interpretation, we argue that in the experiments the observed front velocities were some 15% below the asymptotic front speed and that this is in rough agreement with the predicted slow relaxation of the front speed for the time scales probed in the experiments. We also discuss the possible origin of the unusually large variation of the wavelength of the pattern generated by the front as a function of the dimensionless control parameter.
 Sintayehu Tesfa Physics , 2007, Abstract: We analyze a degenerate three-level cascade laser coupled to an external coherent light via one of the coupler mirrors and vacuum reservoir in the other, employing the stochastic differential equation associated with the normal ordering. We study the squeezing properties and also calculate the mean photon number of the cavity radiation. It turns out that the generated light exhibits up to 98.3% squeezing under certain conditions pertaining to the initial preparation of the superposition and the amplitude of the driving radiation. Moreover, the mean photon number is found to be large where there is a better squeezing. Hence it is believed that the system under consideration can generate an intense squeezed light.
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