Standing-wave Laser Research Articles

A Simple Scheme for Two-Qubit Grover Search in Hot Trapped Ions

An alternative simple scheme is proposed to implement the two-qubit Grover search algorithm in trapped ions by applying a single standing-wave laser pulse during the two-qubit operation. The scheme is insensitive to the heating of vibrational motion, which is important in view of decoherence. Moreover a third auxiliary internal electronic state is eliminated, and the qubit definitions are the same for both ions, which makes the experiment easier and simpler.

Frequency splitting phenomenon of dual transverse modes in a Nd:YAG laser

We observed frequency splitting phenomenon of dual transverse modes (TEM 00q and TEM 01q) in a Nd:YAG microchip standing wave laser utilizing intracavity stress birefringence effects. Four resonance frequencies ( ν 00qe, ν 00qo, ν 01qe, and ν 01qo, respectively) were produced and tuned by changing the diametral compression force applied on the laser crystal. The transverse mode frequency spacing for the same longitudinal mode number (Δ ν trans) was 1.16 GHz, and the magnitude of frequency splitting (Δ ν) ranged from 0 MHz to 1.16 GHz. Based on this phenomenon, a four-mode differential standing wave laser, whose signal characteristics were a little like those of a four-mode differential travelling wave laser gyro however with a much larger frequency splitting range, was produced. The theoretical analysis is in good agreement with the experimental results. This phenomenon not only can be used to make lasers with two or more frequency differences, but also can be used to make high-resolution self-sensing laser sensors (e.g. laser force sensors and laser accelerometers).

Bose–Einstein Condensates in a One-Dimensional Optical Lattice: from Superfluidity to Number-Squeezed States

We study the phase coherence property of Bose−Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza–Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states.

Simulation of Chromium Atom Deposition Pattern in a Gaussain Laser Standing Wave with Different Laser Power

One-dimensional deposition of a neutral chromium atomic beam focused by a near-resonant Gaussian standing-laser field is discussed by using a fourth-order Runge-Kutta type algorithm. The deposition pattern of neutral chromium atoms in a laser standing wave with different laser power is discussed and the simulation result shows that the full width at half maximum (FWHM) of a nanometer stripe is 115 nm and the contrast is 2.5:1 with laser power 3.93 mW; the FWHM is 0.8 nm and the contrast is 27:1 with laser power 16 mW, the optimal laser power; but with laser power increasing to 50 mW, the nanometer structure forms multi-crests and the quality worsens quickly with increasing laser power.

Effects of atomic motion in a standing-wave laser field on the Rabi oscillations

We study the effects of the two-level-atom motion in a standing-wave laser field on the Rabi oscillations. In the presence of the resonance optical Stern–Gerlach effect, the atomic wave packet, centered initially at a node of the standing wave, is shown to evolve in such a way that the atomic population inversion remains zero when the initially de-excited atom moves between the nodes, then collapses to the ground level upon crossing the nodes, and practically returns to zero after that. This coherent population trapping is explained in the dressed-state picture. The Doppler–Rabi resonance, i.e., maximum Rabi oscillations at large values of the atom–field detuning, becomes possible if the detuning is equal to the Doppler shift. A simple formula for the population inversion is derived in the Raman–Nath approximation.

Collective transverse cavity cooling of a dense molecular beam

Based on a classical point particle description, we study light induced transverse collimation and phase space compression of a fast molecular beam traversing the crossover region of a high-Q optical cavity and a standing-wave laser beam. The molecules scatter pump laser light, far detuned from any molecular transition, into the resonant cavity mode. We show that despite a very small probability for this process for a single particle, collective enhancement can lead to significant transverse cooling and collimation above the self-organization threshold. The analytical formulae for this threshold derived from homogeneous one-dimensional (1D) models give surprisingly good estimates for the pulsed 3D case. We compare ring and standing wave cavity geometries and show that phase space compression can be achieved even for extremely small particle field coupling if compensated by a large density and pump power. In the vicinity of the critical point the compression time can be reduced by tailored seeding of the cavity mode or using a second buildup cavity for the pump field.

Fractional resonances in the atom-opticalδ-kicked accelerator

We consider resonant dynamics in a dilute atomic gas falling under gravity through a periodically pulsed standing-wave laser field. Our numerical calculations are based on a Monte Carlo method for an incoherent mixture of noninteracting plane waves, and we show that quantum resonances are highly sensitive to the relative acceleration between the atomic gas and the pulsed optical standing wave. For particular values of the atomic acceleration, we observe fractional resonances. We investigate the effect of the initial atomic momentum width on the fractional resonances and quantify the sensitivity of fractional resonances to thermal effects.

Collisional decoherence in trapped-atom interferometers that use nondegenerate sources

The coherence time, and thus sensitivity, of trapped-atom interferometers that use nondegenerate gases are limited by the collisions between the atoms. An analytic model that describes the effects of collisions between atoms in an interferometer is developed. It is then applied to an interferometer using a harmonically trapped nondegenerate atomic gas that is manipulated with a single set of standing wave laser pulses. The model is used to find the optimal operating conditions of the interferometer and direct Monte Carlo simulation of the interferometer is used to verify the analytic model.

Realizing and Detecting the Quantum Hall Effect without Landau Levels by Using Ultracold Atoms

We design an ingenious scheme to realize Haldane's quantum Hall model without Landau levels by using ultracold atoms trapped in an optical lattice. Three standing-wave laser beams are used to construct a wanted honeycomb lattice, where different on site energies in two sublattices required in the model can be implemented through tuning the phase of one laser beam. The staggered magnetic field is generated from the light-induced Berry phase. Moreover, we establish a relation between the Hall conductivity and the atomic density, enabling us to detect the Chern number with the typical density-profile-measurement technique.

A fast scheme for one-step preparation of a highly entangled cluster state in the ion-trap system

We propose to implement a highly entangled cluster state (HECS) with only one step based on the resonant interactions among N two-level ions and two different standing-wave lasers with a phase difference of π/2. The time for preparation of the HECS is related only to the frequency of the vibrational mode ν (i.e. t=2π/ν). We can ensure that the preparation time is short enough by setting the larger vibrational mode frequency ν to neglect the effect of the decoherence of the qubits. During the process of preparing the HECS, the heating effect of the vibrational mode can be neglected and the initial qubits need only one evolution with the time interval t. The reduced operation steps and the shorter preparation time make the present scheme more feasible in experiments.

Theory of dissipative chaotic atomic transport in an optical lattice

We study dissipative transport of spontaneously emitting atoms in a one-dimensional (1D) standing-wave laser field in the regimes where the underlying deterministic Hamiltonian dynamics is regular and chaotic. A Monte Carlo stochastic wave-function method is applied to simulate semiclassically the atomic dynamics with coupled internal and translational degrees of freedom. It is shown in numerical experiments and confirmed analytically that chaotic atomic transport can take the form either of ballistic motion or a random walking with specific statistical properties. The character of spatial and momentum diffusion in the ballistic atomic transport is shown to change abruptly in the atom-laser detuning regime where the Hamiltonian dynamics is irregular in the sense of dynamical chaos. We find a clear correlation between the behavior of the momentum diffusion coefficient and Hamiltonian chaos probability which is a manifestation of chaoticity of the fundamental atom-light interaction in the diffusivelike dissipative atomic transport. We propose to measure a linear extent of atomic clouds in a 1D optical lattice and predict that, beginning with those values of the mean cloud's momentum for which the probability of Hamiltonian chaos is close to 1, the linear extent of the corresponding clouds should increase sharply. A sensitive dependence of statistical characteristics of dissipative transport on the values of the detuning allows us to manipulate the atomic transport by changing the laser frequency.

Open-Loop Control for Focusing of Neutral Particles by Modulated Optical Field

The dynamics of neutral quantum particles in standing laser wave field is a subject of great interest, stimulated by the focusing problems in nanolithography with cooled atoms. The main task is to obtain different distributions of cooled atoms along the standing optical wave, for instance, to form very narrow periodical structure with a spatial period that is much less than the wavelength of the optical radiation. The effective coherent splitting has been achieved by scattering of atom wave packets by additional optical field with modulated intensity [1–3]. Dynamics of a neutral quantum particle (cooled atom), moving along x, in the field of the perpendicular standing optical wave (along y) can be described in the terms of classical pendulum with a friction [4]: y + βẏ + ω sin y = 0, (1) where overdots stand for time derivatives, the constant β plays the role of the ∗corresponding author; e-mail: nayyersms3@gmail.com

Sub-half-wavelength atom localization via coherence-controlled resonance fluorescence

We present a scheme for sub-half-wavelength localization based on phase-dependent coherent effects on resonance fluorescence. A three-level atom in the Λ configuration is considered. Two metastable states are so separated from each other that the fluorescence spectra from the different transitions do not overlap. Two dipole-allowed transitions and one dipole-forbidden transition are driven by a standing-wave laser field, a travelling-wave laser field and a microwave field, respectively. The spectrum of fluorescence from the standing-wave coupled transition is dependent not only on the position but also on the collective phase of all applied fields. When the phase is varied and fluorescence photons are detected, 50% probability is achieved in a half-wavelength region. This scheme is as efficient as previous ones based on coherence-controlled Autler–Townes spectra.

Confinement effects in a guided-wave atom interferometer with millimeter-scale arm separation

Guided-wave atom interferometers measure interference effects using atoms held in a confining potential. In one common implementation, the confinement is primarily two dimensional, and the atoms move along the nearly free dimension after being manipulated by an off-resonant standing wave laser beam. In this configuration, residual confinement along the nominally free axis can introduce a phase gradient to the atoms that limits the arm separation of the interferometer. We experimentally investigate this effect in detail, and show that it can be alleviated by having the atoms undergo a more symmetric motion in the guide. This can be achieved by either using additional laser pulses or by allowing the atoms to freely oscillate in the potential. With these techniques, we demonstrate interferometer measurement times up to $72\phantom{\rule{0.3em}{0ex}}\mathrm{ms}$ and arm separations up to $0.42\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$ with a well controlled phase, or times of $0.91\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ and separations of $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{mm}$ with an uncontrolled phase.

Performance analysis of intracavity birefringence sensing

The performance of intracavity birefringence sensing by use of a standing-wave laser is theoretically analyzed when the cavity involves internal reflection. On the three-mirror compound cavity model, the condition for converting an optical path length into a laser frequency or a retardation into an optical beat frequency with good linearity and little uncertainty is derived as a function of the cavity parameters and is numerically analyzed.

Quantum Signatures of Chaos in Adiabatic Interaction Between a Trapped Ion and a Laser Standing Wave

We study quantum motion around a classical heteroclinic point of a single trapped ion interacting with a strong laser standing wave. We construct a set of exact coherent states of the quantum system and from the exact solutions reveal that quantum signatures of chaos can be induced by the adiabatic interaction between the trapped ion and the laser standing wave, where the quantum expectation values of position and momentum correspond to the classically chaotic orbit. The chaotic region on the phase space is illustrated. The energy crossing and quantum resonance in time evolution and the exponentially increased Heisenberg uncertainty are found. The results suggest a theoretical scheme for controlling the unstable regular and chaotic motions.

量子模型分析激光驻波原子透镜的像差

量子模型分析激光驻波原子透镜的像差

Manifestation of Hamiltonian chaos in dissipative atomic transport in a standing-wave laser field

We simulate atomic ballistic transport in a standing-wave laser field in the framework of a Monte Carlo stochastic wavefunction approach in which the coherent Hamiltonian evolution is interrupted at random times by spontaneous emission events. It is shown in numerical experiments and confirmed analytically that the character of spatial and momentum diffusion of spontaneously emitting atoms changes abruptly in the atom-laser detuning regime where the deterministic Hamiltonian dynamics has been shown to be chaotic. Thus, we find a manifestation of underlying Hamiltonian chaos in the diffusive-like center-of-mass motion which can be observed in real experiments.

Investigation of electric field effects on C 20 in single molecule experiments

The effect of electric field on single molecule of C 20 in a standing wave laser field is studied. Quantum chemical computations were performed to calculate several properties of C 20. The current study shows that the electric field changes the moments of inertia, bond lengths, dipole moment, force constants, vibrational frequencies, and orientation of C 20. These results confirm that in single molecule experiments the interaction between the molecule and the probing system cannot be neglected.

A scheme for the implementation of unconventional geometric phase gates with trapped ions

We propose a scheme for the realization of unconventional geometric two-qubit phase gates with two identical two-level ions. In the present scheme, the two ions are simultaneously illuminated by a standing-wave laser pulse with its pulse frequency being tuned to the ionic transition. The gate operation time can be much shorter, making the system robust against decoherence. In addition, we choose the appropriate experimental parameters to construct the geometric phase gate in one step, and thus avoid implementing the pure geometric single qubit operation.