Atomic Coherence Effects Research Articles

Entanglement between collective fields via atomic coherence effects

We explore the quantum entanglement between two collective fields via atomic coherence effects. For three-level atoms in $\mathsf{V}$ configuration driven by two applied fields on two-photon resonance, one coherent superposition of the excited states is not excited, which is the counterpart of coherent population trapping. The coherence-induced depopulation makes two cavity fields in each collection combine into a quantum-beat, i.e., equivalently, the difference mode of the two components decouples from the driven atoms. The two sum modes, when they are arranged in the four-wave mixinglike interactions, can be prepared in Einstein-Podolsky-Rosen entangled state. Correspondingly, any two individual fields from different collective modes are entangled with each other. Furthermore, the effects of thermal reservoir and laser linewidths are discussed, and a generalization is given to the case in which each quantum beat involves more than two modes.

Tripartite entanglement in quantum-beat lasers

We examine the quantum correlations at steady state in a three-mode quantum-beat laser that operates well above threshold. The analysis is presented by employing the dressed-atom combination-mode picture, in which only one combination mode of three cavity fields is coupled to the active medium, while the other two combination modes are decoupled. For suitable operating conditions, the coupled mode has the intensity fluctuations below the shot noise, while the two decoupled modes retain in their vacuum states. This determines that all of the original modes exhibit sub-Poissonian statistics. When the system operates well above threshold, the van Loock-Furusawa inequality is satisfied, concluding that the genuine tripartite entanglement among three sub-Poissonian fields is established. Physically, the responsible mechanism is the combined effect of atomic coherence controlled correlated-spontaneous emission and intrinsic feedback.

Coherence transfer between atomic ground states by the technique of stimulated Raman adiabatic passage

We experimentally and theoretically demonstrate that the atomic coherence can be completely transferred or arbitrarily contributed among the different levels in a four-level atomic (tripod) scheme by a group of coupled pulse sequences. This technique can be applied to the information conversion in slow-light storage, quantum logical gates, and so on, which is based on the atomic coherence effect.

Effects of Atomic Coherence and Injected ClassicalField on Chaotic Dynamics of Non-degenerate Cascade Two-PhotonLasers

Based on the cascade two-photon laser dynamic equationderived with the technique of quantum Langevin operators withthe considerations of coherently prepared three-level atoms andthe classical field injected into the cavity, we numerically studythe effects of atomic coherence and classical field on the chaoticdynamics of a two-photon laser. Lyapunov exponent and bifurcationdiagram calculations show that the Lorenz chaos and hyperchaos canbe induced or inhibited by the atomic coherence and the classicalfield via crisis or Hopf bifurcations.

The effect of atomic coherence on absorption in four-level atomic systems: an analytical study

The absorption profile of a four-level ladder atomic system interacting with three driving fields is studied perturbatively and analytical results are presented. Numerical results where the driving field strengths are treated up to all orders are presented. The absorption features are studied in two regimes—(i) the weak middle transition coupling, i.e. Ω2 ≪ Ω1,3 and (ii) the strong middle transition coupling Ω2 ≫ Ω1,3. In case (i), it is shown that the ground-state absorption and the saturation characteristics of the population of level |2⟩ reveal deviation due to the presence of upper level couplings. In particular, the saturation curve for the population of level |2⟩ shows a dip for Ω1 = Ω3. While the populations of levels |3⟩ and |4⟩ show a maxima when this resonance condition is satisfied. Thus the resonance condition provides a criterion for maximally populating the upper levels. A second-order perturbation calculation reveals the nature of these minima (maxima). In the second case, I report two important features: (a) filtering of the Aulter–Townes doublet in the three-peak absorption profile of the ground state, which is achieved by detuning only the uppermost coupling field and (b) control of line-width by controlling the strength of the upper coupling fields. This filtering technique coupled with the control of linewidth could prove to be very useful for high resolution studies.

Mesoscopic multistability with atomic coherence effects

The steady state behaviour describing the interaction of a mesoscopic system of coherently injected two-level Rydberg atoms with a coherently driven single-mode cavity is investigated in both resonant and non-resonant regimes. Multiple-switching effects between the output field states are predicted with the atomic coherent excitation (θ) and relative coherent phase parameter (Φr) of the atomic coherent state . The relation between the transmitted field (x) and the atomic cooperation parameter (C) shows multistable behaviour for some values of the polar and azimuthal angles (θ,). The transverse field feature in the form of a Gaussian beam profile tends to degrade the multistable structure in the (C–x) and the input–output field (x–Y) relations. Micromaser action is analysed for the system with atomic coherence within and without the plane wave approximation.

Atomic coherence effects on optically pumped cesium atoms in static magnetic field

The population difference between ground states F=4 and F=3 is calculated for Cs atoms pumped on the D2 line by a resonant laser beam. The pumping efficiency for Cs atoms in a static magnetic field on two hyperfine transitions (6S1/2F=4→6P3/2F′=3 and F′=4) is calculated for various pump laser intensities. The population difference as a function of the static magnetic field exhibits a dip centered at the zero magnetic field, which corresponds well with the Zeeman coherence between sublevels of the F=4 state. The full-width at half-maximum (FWHM) of the dip as a function of the pump laser intensity shows abnormal power broadening behavior that differs for different hyperfine transitions. We present experimental results that agree with the theoretical calculations.

Optical polarization modulation by competing atomic coherence effects in a degenerate four-level Yb atomic system

A scheme of optical polarization modulation of a linearly polarized infrared probe field is studied in a degenerate four-level Yb atomic system. We have observed an anomalous transmission spectra of two circular polarization components of the probe field exhibiting an enhanced two-photon absorption and a three-photon gain with comparable magnitude, leading to the lossless transmission and enhanced circular dichroism. We carried out a proof-of-principle experiment of fast optical polarization modulation in such a system by modulating the polarization state of the coupling field. The observed enhanced two-photon absorption and three-photon gain of the probe field are due to the result of competing atomic coherence effects.

Destructive Interference in a Λ-Type CoherentlyDriven Mazer

We derive an expression of the interaction between a quantum cavityfield and an ultracold Λ-type three-level atom in which twoupper levels are coupled by a coherent driving field. The effects of thedriving-induced atomic coherence on the atomic emission probability areinvestigated. It is found that, due to the driving-induced atomiccoherence, there are two transition channels for the atom interactingwith the cavity field. Between the two transition channels, there is aquantum interference, which is a destructive interference. Thisdestructive quantum interference suppresses the emission of the atom.The atomic emission probability decreases with the increasing drivingfield.

Atomic-coherence effect on the Jaynes-Cummings model with atomic motion

The nonlinear transient effects, similar to self-induced transparency and adiabatic following, are studied for a moving two-level atom that is entering into an ideal microwave cavity in a coherent superposition of its states. The atom undergoes a one-photon transition in the cavity, sustaining a spatial field distribution for a single-mode coherent (or thermal or Fock state) field. For some particular choice of parameters of atomic coherence, removal of an appreciable amount of field energy from the cavity could be observed.

Role of atomic coherence effects in four-wave mixing using autoionizing resonances

The generation of tunable, nanosecond-pulsed extreme-ultraviolet (EUV) light $(84.92\mathrm{nm}$ to $84.97\mathrm{nm}$ $\ensuremath{\sim}14.6\mathrm{eV})$ using four-wave mixing in optically deep krypton gas was investigated experimentally and theoretically. The sum-frequency mixing scheme generated light from two overlapping autoionizing resonances, ${17s}^{\ensuremath{'}}$ and ${15d}^{\ensuremath{'}}$. We investigated whether the laser-induced atomic coherence effect of electromagnetically induced transparency (EIT) could enhance the intensity of the EUV light generated. The maximum EUV output was seen from the region where the ${15d}^{\ensuremath{'}}$ autoionizing resonance has a transparency window due to Fano-type quantum interference. An analytical model using appropriate atomic parameters explains how background absorption can prevent EIT enhancement of EUV generation; and shows how a background Raman-like coupling term in the nonlinear susceptibility can well describe the measured EUV generation spectrum.

Generation of dipole squeezing in a two-mode system with entangled coherent states of a quantized electromagnetic field

Two-mode quantized electromagnetic fields can be entangled and admit a large number of coherent states. In this paper, we consider a two-mode system that consists of a two-level atom interacting with a two-mode quantized electromagnetic field, which is initially prepared in an entangled two-mode coherent state, via a nondegenerate two-photon process in a lossless cavity. We study the quantum fluctuations in the two-mode system and investigate in detail the effects of detuning, Stark shift and atomic coherence on atomic dipole squeezing (ADS). We show that ADS strongly depends on the atomic coherence. It is found that the stronger the correlations between the two modes are involved, the more the ADS could be generated. The detuning or Stark shift has a destructive effect on ADS, but the combined effect of the detuning and Stark shift may lead to a regular, periodical and strong ADS pattern.

From laser-induced line narrowing to electromagnetically induced transparency in a Doppler-broadened system

The laser-induced line narrowing effect in Doppler broadened systems was discovered thirty years ago. We have revisited this effect to determine its role for dense gases where recent experimental studies have found many intriguing atomic coherence effects. Using the density matrix approach, we study the width of electromagnetically induced transparency under different regimes of broadening.

Generation of higher-order atomic dipole squeezing in a high-Q micromaser cavity. (VIII). Multi-photon interaction

In our preceding serial works, we have investigated the generation of higher-order atomic dipole squeezing (HOADS) in a high-Q micromaser cavity, discussing the effects of dynamic Stark shift, atomic damping, atomic coherence and nonlinear one-photon processes and different initial states (for example, correlated and uncorrelated states, superposition states, squeezed vacuum). In this paper, we continue to study HOADS in a high-Q micromaser cavity, but consider that the atom interacts with the optical field via a multi-photon transition process and that the initial atom is arbitrarily prepared. For a vacuum initial field, we demonstrate that HOADS cannot occur if the atom is initially prepared in a chaotic state and that a coherent atomic state generates less efficient and stable HOADS than an arbitrary one. It is found that large detuning may lead to enhanced and strong HOADS.

COHERENT TWO-PHOTON PULSE PROPAGATION THROUGH A COHERENTLY PREPARED MEDIUM

Propagation of pulses through a medium comprising of coherently prepared two-level atoms undergoing two-photon transition has been studied using Maxwell–Bloch equations. The solution of the electromagnetic field envelopes has been obtained under various conditions and the effect of initial atomic coherence is clearly brought out in these solutions.

Atomic Coherence in the Micromaser Injected withSlow V-type Three-State Atoms: Emission Probability

The effects of atomic coherence on the single-modetwo-photon micromaser injected with slow V-type three-state atoms arestudied for the first time. It is shown that the atomic coherence can modifythe atomic emission probability. The effects of the atomiccentre-of-mass momentum, the cavity length and other parameters are alsostudied.

Pump-coupled micromasers: coherent and incoherent coupling

We consider two micromasers coupled via the pumping beam of initially excited two-level atoms traversing the two cavities in a sequence. The atomic populations and coherences pumping the second micromaser are, therefore, prepared by the first one. To separate the effects of atomic coherence we compare the two cases of incoherent and coherent coupling, i.e., when the states of the atoms are measured between the cavities (`which path') and when not. Using an exact solution for the incoherent case, we find that the second micromaser undergoes abrupt transitions between distinct phases of the photon statistics triggered, via injected absorption, by the first one. In the case of coherent coupling, we consider the exact master equation of the fields first and, after finding its nonlinear expansion, apply standard Fokker–Planck techniques. Complementing the nonlinear treatment, we also employ numerical simulations to investigate a different regime of the system. In addition to the incoherent effects, we find that atomic coherence significantly modifies the mean and the variance of the photon number of the second field and, at the same time, establishes first order (phase locking) and second order correlations between the two fields at steady state. The time evolution exhibits abrupt jumps in the locking of the relative phase between zero and π accompanied by shut-offs of the second micromaser. The coherence effects are particularly important in the region of small pumping parameters.

Four-wave mixing under conditions of Doppler-free resonance induced by strong radiation

The possibilities of enhancing the nonlinear optical response of a gaseous medium and the radiation conversion efficiency in four-wave mixing processes through the use of atomic coherence effects and the induced elimination of the Doppler broadening of resonances are investigated. Numerical illustrations of the effects are given for experiments in progress.

Sub-Doppler absorption resonances induced by strong radiation

New possibilities are demonstrated for eliminating uncompensated Doppler broadening in different types of nonlinear optical processes by means of atomic coherence effects in strong electromagnetic fields are demonstrated.

Atomic coherence effects in the ion-trap laser

The influence of atomic coherence effects on the statistical and spectral properties of the ion-trap laser is investigated. Various pump configurations are considered for a realistic level scheme using a Ca + ion. Compared to previous suggestions, 50% more output is obtained.