Intrinsic Cavity QED and Emergent Quasi-Normal Modes for Single Photon

We propose a special cavity design that is constructed by terminating a one-dimensional waveguide with a perfect mirror at one end and doping a two-level atom at the other. We show that this atom plays the intrinsic role of a semi-transparent mirror for single photon transports such that quasi-normal modes (QNM's) emerge spontaneously in the cavity system. This atomic mirror has its reflection coefficient tunable through its level spacing and its coupling to the cavity field, for which the cavity system can be regarded as a two-end resonator with a continuously tunable leakage. The overall investigation predicts the existence of quasi-bound states in the waveguide continuum. Solid state implementations based on a dc-SQUID circuit and a defected line resonator embedded in a photonic crystal are illustrated to show the experimental accessibility of the generic model.Comment: 4 pages,5 figures, Comments welcom

An analysis of dynamical suppression of spontaneous emission

It has been shown recently [see, for example, S.-Y. Zhu and M. O. Scully, Phys. Rev. Lett. {\bf 76}, 388 (1996)] that a dynamical suppression of spontaneous emission can occur in a three-level system when an external field drives transitions between a metastable state and {\em two} decaying states. What is unusual in the decay scheme is that the decaying states are coupled directly by the vacuum radiation field. It is shown that decay dynamics required for total suppression of spontaneous emission necessarily implies that the level scheme is isomorphic to a three-level lambda system, in which the lower two levels are {\em both} metastable, and each is coupled to the decaying state. As such, the total suppression of spontaneous emission can be explained in terms of conventional dark states and coherent population trapping.Comment: 8 pages, 3 figure

Optimal squeezing, pure states, and amplification of squeezing in resonance fluorescence

It is shown that 100% squeezed output can be produced in the resonance fluorescence from a coherently driven two-level atom interacting with a squeezed vacuum. This is only possible for $N=1/8$ squeezed input, and is associated with a pure atomic state, i.e., a completely polarized state. The quadrature for which optimal squeezing occurs depends on the squeezing phase $\Phi ,$ the Rabi frequency $\Omega ,$ and the atomic detuning $\Delta$. Pure states are described for arbitrary $\Phi ,$ not just $\Phi =0$ or $\pi$ as in previous work. For small values of $N,$ there may be a greater degree of squeezing in the output field than the input - i.e., we have squeezing amplification.Comment: 6 pages & 7 figures, Submitted to Phys. Rev.

Superconductivity of lanthanum revisited: enhanced critical temperature in the clean limit

The thickness dependence of the superconducting energy gap $\Delta_{\rm{La}}$ of double hexagonally close packed (dhcp) lanthanum islands grown on W(110) is studied by scanning tunneling spectroscopy, from the bulk to the thin film limit. Superconductivity is suppressed by the boundary conditions for the superconducting wavefunction at the surface and W/La interface, leading to a linear decrease of the critical temperature $T_c$ as a function of the inverse film thickness. For thick, bulk-like films, $\Delta_{\rm{La}}$ and $T_c$ are 40% larger as compared to literature values of dhcp La measured by other techniques. This finding is reconciled by examining the effects of surface contamination as probed by modifications of the surface state, suggesting that the large $T_c$ originates in the superior purity of the samples investigated here.Comment: 14 pages, 7 figure

Construction of localized wave functions for a disordered optical lattice and analysis of the resulting Hubbard model parameters

We propose a method to construct localized single particle wave functions using imaginary time projection and thereby determine lattice Hamiltonian parameters. We apply the method to a specific disordered potential generated by an optical lattice experiment and calculate for each instance of disorder, the equivalent lattice model parameters. The probability distributions of the Hubbard parameters are then determined. Tests of localization and eigen-energy convergence are examined.Comment: 10 pages, 16 figure

Monte Carlo simulations of Rb2MnF4{\rm Rb_2MnF_4}, a classical Heisenberg antiferromagnet in two-dimensions with dipolar interaction

We study the phase diagram of a quasi-two dimensional magnetic system ${\rm Rb_2MnF_4}$ with Monte Carlo simulations of a classical Heisenberg spin Hamiltonian which includes the dipolar interactions between ${\rm Mn}^{2+}$ spins. Our simulations reveal an Ising-like antiferromagnetic phase at low magnetic fields and an XY phase at high magnetic fields. The boundary between Ising and XY phases is analyzed with a recently proposed finite size scaling technique and found to be consistent with a bicritical point at T=0. We discuss the computational techniques used to handle the weak dipolar interaction and the difference between our phase diagram and the experimental results.Comment: 13 pages 18 figure

Creep motion of a domain wall in the two-dimensional random-field Ising model with a driving field

With Monte Carlo simulations, we study the creep motion of a domain wall in the two-dimensional random-field Ising model with a driving field. We observe the nonlinear fieldvelocity relation, and determine the creep exponent {\mu}. To further investigate the universality class of the creep motion, we also measure the roughness exponent {\zeta} and energy barrier exponent {\psi} from the zero-field relaxation process. We find that all the exponents depend on the strength of disorder.Comment: 5 pages, 4 figure

Mosaic spin models with topological order

We study a class of two-dimensional spin models with the Kitaev-type couplings in mosaic structure lattices to implement topological orders. We show that they are exactly solvable by reducing them to some free Majorana fermion models with gauge symmetries. The typical case with a 4-8-8 close packing is investigated in detail to display the quantum phases with Abelian and non-Abelian anyons. Its topological properties characterized by Chern numbers are revealed through the edge modes of its spectrum.Comment: 4 pages, 3 figures. Final version to appear in Phys. Rev. B as a Rapid Communicatio

Deflection of Slow Light by Magneto-Optically Controlled Atomic Media

We present a semi-classical theory for light deflection by a coherent $\Lambda$-type three-level atomic medium in an inhomogeneous magnetic field or an inhomogeneous control laser. When the atomic energy levels (or the Rabi coupling by the control laser) are position-dependent due to the Zeeman effect by the inhomogeneous magnetic field (or the inhomogeneity of the control field profile), the spatial dependence of the refraction index of the atomic medium will result in an observable deflection of slow signal light when the electromagnetically induced transparency happens to avoid medium absorption. Our theoretical approach based on Fermat's principle in geometrical optics not only provides a consistent explanation for the most recent experiment in a straightforward way, but also predicts the new effects for the slow signal light deflection by the atomic media in an inhomogeneous off-resonant control laser field.Comment: 4 pages, 3 figure