Showing papers on "Atomic coherence published in 1994"

Quantum sensitivity limits of an optical magnetometer based on atomic phase coherence.

Abstract: An optical magnetometer based on atomic coherence effects is analyzed using a quantum Langevin approach. The large dispersion of a phase-coherent atomic medium (``phaseonium'') at a point of vanishing absorption is used to detect magnetic level shifts via optical phase measurements in a Mach-Zehnder interferometer with sensitivities potentially superior to state-of-the-art devices. Effects of Doppler broadening and fluctuations of the driving field are discussed and a comparison to standard optical-pumping magnetometers is made.

The Birth of a Phase-cat

Abstract: We present a recipe for constructing a phase-cat, that is a superposition of two coherent states of identical phase but different amplitudes. The method relies on an effective rotation of an amplitude-cat, that is a superposition of two coherent states with identical amplitudes but different phases. We create the amplitude-cat by a dispersive atom-field interaction and achieve its effective rotation via the combination of two beam splitters and a phase shifter. We optimize the amount of phase narrowing by choosing the appropriate initial atomic superposition and by performing the appropriate delayed measurement of the final atomic coherence.

Coherent transfer of photon momentum by adiabatic following in a dark state

Abstract: We demonstrate a new technique for the mechanical manipulation of atoms with light that may be used to deflect or split an atomic beam. This technique depends on the existence of an internal superposition state of the atom that is 'dark' to resonant excitation by a particular light field. An atom in a dark state may adiabatically follow a slowly varying light field in such a way that both the internal state and the atom's momentum are changed. Because the dark state never absorbs or fluoresces, the atomic coherence, necessary for atom interferometry, is preserved. We use laser-cooled Cs atoms to demonstrate the transfer of 8 photon momenta from the slowly varying laser field to the atom.

Atomic coherence effects which produce superluminal (but causal) propagation of wavepackets

Abstract: Analytic, limited-bandwidth signals, e.g. Gaussian wavepackets, whose frequencies lie in a transparent spectral window far below the resonance of an amplifying atomic medium, can propagate with phase, group, energy and 'signal' velocities (as defined by Sommerfeld and Brillouin) all exceeding the vacuum speed of light c. This 'superluminal' propagation may occur without significant distortion or gain. The front velocity, however, is not superluminal, and therefore Einstein causality is not violated. Applications will be discussed, including the possibility of using superluminal atomic coherence in condensed matter (e.g. macroscopic mass currents in superfluid helium which arise from vortex motions) for efficient gravitational antennae.

Atomic coherence effects within the sodium D1 manifold. II. Coherent optical pumping

Abstract: For pt. I see ibid. p. 231, 1994. We consider optical pumping in the multilevel sodium D1 manifold by several coherent light fields. Coherence between atomic states is taken into account by solving the complete density matrix equations. The manifestation of population trapping and the variation of transmitted light intensity are predicted numerically and verified experimentally for the sodium D1 line. The influence of relaxation and Doppler broadening is elucidated. The interaction of a strong and a weak field is shown to create electromagnetically induced transparency.

Entropy Evolution of the Bimodal Field Interacting with an Effective Two-level Atom Via the Raman Transition

Abstract: The properties of entropy evolution of the bimodal field interacting with an effective two-level atom via the Raman transition are studied. The influences of the initial average photon number and of the atomic coherence on the evolution of the bimodal field entropy are examined. It is shown that the bimodal field is in a pure state only under certain conditions in the early stages of time evolution and later tends to a statistical mixture state with maximum entropy values; the bimodal field remains strongly entangled with the atom.

Atomic dipole squeezing and emission spectra of a nondegenerate two-photon Jaynes-Cummings model in the presence of Stark shift

Abstract: The atomic dipole squeezing and the emission spectra in a nondegenerate two-photon Jaynes–Cummings model in the presence of Stark shift for various field inputs are studied. The percentage duration of the atomic dipole squeezing is greatly enhanced by the inclusion of the Stark shift. The emission spectra show an asymmetric central two-peak structure that is quite different from that in the absence of the Stark shift. When the fields are initially in the coherent state, asymmetric coherent sidebands emerge. The effect of atomic coherence on dipole squeezing and the emission spectrum have also been incorporated

Intensity characteristics of inversionless lasers from induced atomic coherence

Abstract: We analyze a laser system consisting of N closed three-level atoms confined in a single-mode cavity and derive the conditions for the onset of lasing without inversion or with inversion. We calculate the steady-state gain and lasing in the system and show that far above the lasing threshold, depending on the pumping and decay rates, the inversionless laser may operate in three different regimes, where the intensity of the laser depends linearly on N, is proportional to \ensuremath{\surd}N , or independent of N.

Atomic coherence effects within the sodium D1 manifold. I. Creation of coherence and dressed state analysis

Abstract: The connection and similarity between two different models for lasing without inversion are studied, and various dressed state pictures enlighten its physical origin. Recent experiments on coherence effects in sodium are reviewed. The existence of atomic coherence in these experiments is critically examined. It is found that the hyperfine structure and the coupling coefficients within the sodium D1 manifold are of crucial importance.

The effect of the homogeneous broadening on the propagation of the light pulses

Abstract: The propagation of resonant pulses in a two-level homogeneously broadened atomic medium is analyzed. The pulses with the duration comparable with the atomic coherence relaxation time are considered. The effects of the long pulse area stabilization and destabilization are reported. The numerical simulation is performed.

Squeezing from ghost transitions

Abstract: We show that significant squeezing in a strong signal light field can be generated with three-level atoms in a ghost-transition setup by tuning a weak probe beam inside the Autler-Townes doublet created by the strong signal light. Close to the Rabi level, i.e., within the absorption line, processes involving both amplitude quadratures become important. Significant atomic two-photon coherence provides a vehicle for signal-amplitude fluctuations to trigger fluctuations in the probe amplitude. Subsequently, atomic coherence will feed these probe fluctuations back into the signal and enable substantial noise suppression.

Atomic coherence effects within the sodium D1 manifold. III: Lasing without inversion via population trapping

Abstract: Transient lasing without inversion has been experimentally demonstrated in sodium vapour. The principle of this atomic coherence effect can be well understood from the theory of a simple four-level system. The experimental results match with numerical simulations which take the complete hyperfine structure of the sodium D1 line into account. The differences between our system and a Raman laser are discussed.

Nonlinear theory of a laser with injected atomic coherence.

Abstract: The influence of injected atomic coherence on a laser's operation is discussed by analyzing the semiclassical equations of motion of this system. Both stationary-steady-state and time-dependent regimes of operation are investigated. We present the dependence of the stationary laser intensity and phase on the external parameters (population inversion, amplitude of atomic coherence, and detuning). For small cavity-field detuning and large atomic coherence, both frequency and phase locking occurs. The laser frequency is locked to the atomic frequency, and the phase is locked to a value determined primarily by the phase of the atomic coherence. Under certain conditions, in the inverted regime, the output intensity is an ssS-shaped function of the atomic coherence, leading to the possibility of a bistable behavior. However, only a portion of the bistable curve gives stable stationary operation, and in critical points (the location of which depends crucially on the external parameters) time-dependent instabilities branch away. When the detuning is larger than a critical value there is neither phase nor frequency locking. We find that the time-dependent behavior of the laser intensity in this case is oscillatory (quasiperiodic), and show that there is a stable limit cycle in the phase plane of the quadratures. There is a small parameter region where a stationary steady state and an oscillatory state may coexist. We also consider the nonlinear quantum theory of a laser with injected atomic coherence, and include the effect of pumping statistics. We derive the Fokker-Planck equation for the P representation, and express the noise in terms of moments. We find that in the steady state the intensity noise can be suppressed below the shot-noise limit but that the phase fluctuations are not affected by pump regularity. For nonzero detuning, we find that transient squeezing of the phase fluctuations is possible.

Gain without inversion in four level atoms using pulsed lasers

Abstract: We present results of a numerical calculation of gain without inversion in the transient regime. We show that atomic coherence and gain without population inversion can be induced on time scales short compared to atomic radiative lifetimes. We also describe the process in terms of transient dressed states.

THE ATOMIC COHERENCE AND MODEL SIMULATION OF AMORPHOUS Si 3 N 4

Abstract: The atomic coherence rule of solids is used in the model simulation of the amorphous Si 3 N 4 , the results are compared with experiment. The possible construction of the real amorphous Si 3 N 4 and the validity of coherence rule used in the model simulation of amorphous are discussed.

Enhanced interactions in atomic coherence

Abstract: In a quantum coherent system, the effect of the dipole-dipole interactions is calculated for nearest neighbours. A mean theory is used in a lattice gas approximation. It is found that the dipole interaction is negligible for low pressure but begins to have noticeable effects on the susceptibility at a number density of about 1016 cm-3.

Transfer of atomic coherence in a micromaser

Abstract: tion system. The calculated maximum squeezing for our OPA is 6 dB. The degree of squeezing is presently limited by imperfect modematching at the homodyne detector. Apart from interferometry, the present source of squeezed vacuum has other applications. It can be employed to realize quantum-nondemolition measurements, and, by coherent superposition of squeezed vacuum with bright light, squeezed bright light can be generated.