Preparation of nondegenerate coherent superpositions in a three-state ladder system assisted by Stark Shifts

We propose a technique to prepare coherent superpositions of two nondegenerate quantum states in a three-state ladder system, driven by two simultaneous fields near resonance with an intermediate state. The technique, of potential application to enhancement of nonlinear processes, uses adiabatic passage assisted by dynamic Stark shifts induced by a third laser field. The method offers significant advantages over alternative techniques: (\i) it does not require laser pulses of specific shape and duration and (\ii) it requires less intense fields than schemes based on two-photon excitation with non-resonant intermediate states. We discuss possible experimental implementation for enhancement of frequency conversion in mercury atoms.Comment: 22 pages, 8 figures, 1 table, submitted to PHys. Rev.

Photoionization Suppression by Continuum Coherence: Experiment and Theory

We present experimental and theoretical results of a detailed study of laser-induced continuum structures (LICS) in the photoionization continuum of helium out of the metastable state 2s $^1S_0$. The continuum dressing with a 1064 nm laser, couples the same region of the continuum to the {4s $^1S_0$} state. The experimental data, presented for a range of intensities, show pronounced ionization suppression (by as much as 70% with respect to the far-from-resonance value) as well as enhancement, in a Beutler-Fano resonance profile. This ionization suppression is a clear indication of population trapping mediated by coupling to a contiuum. We present experimental results demonstrating the effect of pulse delay upon the LICS, and for the behavior of LICS for both weak and strong probe pulses. Simulations based upon numerical solution of the Schr\"{o}dinger equation model the experimental results. The atomic parameters (Rabi frequencies and Stark shifts) are calculated using a simple model-potential method for the computation of the needed wavefunctions. The simulations of the LICS profiles are in excellent agreement with experiment. We also present an analytic formulation of pulsed LICS. We show that in the case of a probe pulse shorter than the dressing one the LICS profile is the convolution of the power spectra of the probe pulse with the usual Fano profile of stationary LICS. We discuss some consequences of deviation from steady-state theory.Comment: 29 pages, 17 figures, accepted to PR

Phase shifts in nonresonant coherent excitation

Far-off-resonant pulsed laser fields produce negligible excitation between two atomic states but may induce considerable phase shifts. The acquired phases are usually calculated by using the adiabatic-elimination approximation. We analyze the accuracy of this approximation and derive the conditions for its applicability to the calculation of the phases. We account for various sources of imperfections, ranging from higher terms in the adiabatic-elimination expansion and irreversible population loss to couplings to additional states. We find that, as far as the phase shifts are concerned, the adiabatic elimination is accurate only for a very large detuning. We show that the adiabatic approximation is a far more accurate method for evaluating the phase shifts, with a vast domain of validity; the accuracy is further enhanced by superadiabatic corrections, which reduce the error well below $10^{-4}$. Moreover, owing to the effect of adiabatic population return, the adiabatic and superadiabatic approximations allow one to calculate the phase shifts even for a moderately large detuning, and even when the peak Rabi frequency is larger than the detuning; in these regimes the adiabatic elimination is completely inapplicable. We also derive several exact expressions for the phases using exactly soluble two-state and three-state analytical models.Comment: 10 pages, 7 figure

Stimulated Raman adiabatic passage analogs in classical physics

Stimulated Raman adiabatic passage (STIRAP) is a well established technique for producing coherent population transfer in a three-state quantum system. We here exploit the resemblance between the Schrodinger equation for such a quantum system and the Newton equation of motion for a classical system undergoing torque to discuss several classical analogs of STIRAP, notably the motion of a moving charged particle subject to the Lorentz force of a quasistatic magnetic field, the orientation of a magnetic moment in a slowly varying magnetic field, the Coriolis effect and the inertial frame dragging effect. Like STIRAP, those phenomena occur for counterintuitively ordered field pulses and are robustly insensitive to small changes in the interaction properties

Light dressed-excitons in an incoherent-electron sea: Evidence for Mollow-triplet and Autler-Townes doublet

We demonstrate that the interaction between excitons and a sea of incoherent electrons does not preclude excitons dressing by light. We investigate the role of exciton-electron scattering in the light dressing by measuring the dynamical absorption spectrum of a modulation-doped CdTe quantum well, which shows a clear evidence for significant electron scattering of the excitonic states. We show the occurrence of dressed and correlated excitons by detecting quantum coherent interferences through excitonic Autler-Townes doublet and ac Stark splitting, which evolves to Mollow triplet with gain. We also evidence the partial inhibition of the electron-exciton scattering by exciton-light coupling

A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium

We present the results of a velocity correlation study of the high latitude cloud MBM16 using a fully sampled $^{12}$CO map, supplemented by new $^{13}$CO data. We find a correlation length of 0.4 pc. This is similar in size to the formaldehyde clumps described in our previous study. We associate this correlated motion with coherent structures within the turbulent flow. Such structures are generated by free shear flows. Their presence in this non-star forming cloud indicates that kinetic energy is being supplied to the internal turbulence by an external shear flow. Such large scale driving over long times is a possible solution to the dissipation problem for molecular cloud turbulence.Comment: Uses AAS aasms4.sty macros. Accepted for publication in Ap

The effects of an extra U(1) axial condensate on the radiative decay eta' --> gamma gamma at finite temperature

Supported by recent lattice results, we consider a scenario in which a U(1)-breaking condensate survives across the chiral transition in QCD. This scenario has important consequences on the pseudoscalar-meson sector, which can be studied using an effective Lagrangian model. In particular, generalizing the results obtained in a previous paper (where the zero-temperature case was considered), we study the effects of this U(1) chiral condensate on the radiative decay eta' --> gamma gamma at finite temperature.Comment: 15 pages, LaTeX fil

Steady-state crystallization of Rydberg excitations in an optically driven lattice gas

We study resonant optical excitations of atoms in a one-dimensional lattice to the Rydberg states interacting via the van der Waals potential which suppresses simultaneous excitation of neighboring atoms. Considering two- and three-level excitation schemes, we analyze the dynamics and stationary state of the continuously-driven, dissipative many-body system employing time-dependent density-matrix renormalization group (t-DMRG) simulations. We show that two-level atoms can exhibit only nearest neighbor correlations, while three-level atoms under dark-state resonant driving can develop finite-range crystalline order of Rydberg excitations. We present an approximate rate equation model whose analytic solution yields qualitative understanding of the numerical results.Comment: 5 pages,3 figure

Entanglement reciprocation between qubits and continuous variables

We investigate how entanglement can be transferred between qubits and continuous variable (CV) systems. We find that one ebit borne in maximally entangled qubits can be fully transferred to two CV systems which are initially prepared in pure separable Gaussian field with high excitation. We show that it is possible, though not straightforward, to retrieve the entanglement back to qubits from the entangled CV systems. The possibility of deposition of multiple ebits from qubits to the initially unentangled CV systems is also pointed out.Comment: 4 pages, 3 figures, RevTeX

Diffractive Optics for Gravitational Wave Detectors

All-reflective interferometry based on nano-structured diffraction gratings offers new possibilities for gravitational wave detection. We investigate an all-reflective Fabry-Perot interferometer concept in 2nd order Littrow mount. The input-output relations for such a resonator are derived treating the grating coupler by means of a scattering matrix formalism. A low loss dielectric reflection grating has been designed and manufactured to test the properties of such a grating cavity