Publications (You can locate these works by entering H. Y. Ling as author in the APS website: .)



Superfluid pairing in a mixture of a spin-polarized Fermi gas and a dipolar condensate

Ben Kain and Hong Y. Ling

Phys. Rev. A 85, 013631 (2012) – Published January 23, 2012

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A mixture of a spin-polarized Fermi gas and a dipolar Bose-Einstein condensate is considered in which s-wave scattering between fermions and the quasiparticles of the dipolar condensate can result in an effective attractive Fermi-Fermi interaction long-range and anisotropic in nature and tunable by the dipolar interaction. It is shown that such an interaction can significantly increase the prospect of realizing a superfluid with a gap parameter characterized with a coherent superposition of all odd partial waves. In the spirit of the Hartree-Fock-Bogoliubov mean-field approach, a theory is formulated that allows the estimation of the critical temperature when the anisotropic Fock potential is taken into consideration and the determination of the system parameters that optimize the critical temperature at which such a superfluid emerges before the system begins to phase separate.

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Cosmological inhomogeneities with Bose-Einstein condensate dark matter

Ben Kain and Hong Y. Ling

Phys. Rev. D 85, 023527 (2012) – Published January 23, 2012

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We consider the growth of cosmological perturbations to the energy density of dark matter during matter domination when dark matter is a scalar field that has undergone Bose-Einstein condensation. We study these inhomogeneities within the framework of both Newtonian gravity, where the calculation and results are more transparent, and General Relativity. The direction we take is to derive analytical expressions, which can be obtained in the small pressure limit. Throughout we compare our results to those of the standard cosmology, where dark matter is assumed pressureless, using our analytical expressions to showcase precise differences. We find, compared to the standard cosmology, that Bose-Einstein condensate dark matter leads to a scale factor, gravitational potential and density contrast that increase at faster rates.

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Singlet and triplet superfluid competition in a mixture of two-component Fermi and one-component dipolar Bose gases

Ben Kain and Hong Y. Ling

Phys. Rev. A 83, 061603 (2011) – Published June 22, 2011

Cited 1 time

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We consider a mixture of two-component Fermi and (one-component) dipolar Bose gases in which both dipolar interaction and s-wave scattering between fermions of opposite spins are tunable. We show that in the long-wavelength limit, the anisotropy in the Fermi-Fermi interaction induced by phonons of the dipolar condensate can strongly enhance the scattering in the triplet channel. We investigate in detail the conditions for achieving optimal critical temperature at which the triplet superfluid begins to compete with the singlet superfluid.

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Measurement backaction on the quantum spin-mixing dynamics of a spin-1 Bose-Einstein condensate

Keye Zhang, Lu Zhou, Hong Y. Ling, Han Pu, and Weiping Zhang

Phys. Rev. A 83, 063624 (2011) – Published June 20, 2011

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We consider a small F=1 spinor condensate inside an optical cavity driven by an optical probe field, and subject the output of the probe to a homodyne detection, with the goal of investigating the effect of measurement backaction on the spin dynamics of the condensate. Using the stochastic master equation approach, we show that the effect of backaction is sensitive to not only the measurement strength but also the quantum fluctuation of the spinor condensate. The same method is also used to estimate the atom numbers below which the effect of backaction becomes so prominent that extracting spin dynamics from this cavity-based detection scheme is no longer practical.

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Landau-Ginzburg perspective of finite-temperature phase diagrams of a two-component Fermi-Bose mixture

Michael Fodor and Hong Y. Ling

Phys. Rev. A 82, 043610 (2010) – Published October 15, 2010

Cited 1 time

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We consider a mixture of two-component Fermi and (one-component) Bose gases under the repulsive Bose-Fermi and attractive Fermi-Fermi interactions. We perform a systematic study of the finite-temperature phase diagrams in the chemical potential space, identifying, using the Landau-Ginzburg theory, the features generic to the phase diagrams within the validity of our model. We apply the theory to explore the physics of correlated BCS pairing among fermions in a tightly confined trap surrounded by a large Bose-Einstein condensate gas.

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Vortices in Bose-Einstein condensate dark matter

Ben Kain and Hong Y. Ling

Phys. Rev. D 82, 064042 (2010) – Published September 30, 2010

Cited 5 times

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If dark matter in the galactic halo is composed of bosons that form a Bose-Einstein condensate, then it is likely that the rotation of the halo will lead to the nucleation of vortices. After a review of the Gross-Pitaevskii equation, the Thomas-Fermi approximation and vortices in general, we consider vortices in detail. We find strong bounds for the boson mass, interaction strength, the shape and quantity of vortices in the halo, the critical rotational velocity for the nucleation of vortices and, in the Thomas-Fermi regime, an exact solution for the mass density of a single, axisymmetric vortex.

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Spin dynamics and domain formation of a spinor Bose-Einstein condensate in an optical cavity

Lu Zhou, Han Pu, Hong Y. Ling, Keye Zhang, and Weiping Zhang

Phys. Rev. A 81, 063641 (2010) – Published June 30, 2010

Cited 5 times

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We consider a ferromagnetic spin-1 Bose-Einstein condensate (BEC) dispersively coupled to a unidirectional ring cavity. We show that the ability of the cavity to modify, in a highly nonlinear fashion, matter-wave phase shifts adds an additional dimension to the study of spinor condensates. In addition to demonstrating strong matter-wave bistability as in our earlier publication [ L. Zhou et al. Phys. Rev. Lett. 103 160403 (2009)], we show that the interplay between atomic and cavity fields can greatly enrich both the physics of critical slowing down in spin-mixing dynamics and the physics of spin-domain formation in spinor condensates.

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Achieving ground-state polar molecular condensates by chainwise atom-molecule adiabatic passage

Jing Qian, Weiping Zhang, and Hong Y. Ling

Phys. Rev. A 81, 013632 (2010) – Published January 29, 2010

Cited 3 times

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We generalize the idea of chainwise stimulated Raman adiabatic passage (STIRAP) [ Kuznetsova et al. Phys. Rev. A 78 021402 (2008)] to a photoassociation-based chainwise atom-molecule system, with the goal of directly converting two-species atomic Bose-Einstein condensates (BEC) into a ground polar molecular BEC. We pay particular attention to the intermediate Raman laser fields, a control knob inaccessible to the usual three-level model. We find that an appropriate exploration of both the intermediate laser fields and the stability property of the atom-molecule STIRAP can greatly reduce the power demand on the photoassociation laser, a key concern for STIRAPs starting from free atoms due to the small Franck-Condon factor in the free-bound transition.

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Matter-wave bistability in coupled atom-molecule quantum gases

Lei Jiang, Han Pu, Andrew Robertson, and Hong Y. Ling

Phys. Rev. A 81, 013619 (2010) – Published January 20, 2010

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We study the matter-wave bistability in coupled atom-molecule quantum gases, in which heteronuclear molecules are created via an interspecies Feshbach resonance involving either two-species Bose or two-species Fermi atoms at zero temperature. We show that the resonant two-channel Bose model is equivalent to the nondegenerate parametric down-conversion in quantum optics, while the corresponding Fermi model can be mapped to a quantum optics model that describes a single-mode laser field interacting with an ensemble of inhomogeneously broadened two-level atoms. Using these analogies and the fact that both models are subject to the Kerr nonlinearity due to the two-body s-wave collisions, we show that under proper conditions, the population in the molecular state in both models can be made to change with the Feshbach detuning in a bistable fashion.

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Cavity-Mediated Strong Matter Wave Bistability in a Spin-1 Condensate

Lu Zhou, Han Pu, Hong Y. Ling, and Weiping Zhang

Phys. Rev. Lett. 103, 160403 (2009) – Published October 15, 2009

Cited 13 times

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We study matter-wave bistability in a spin-1 Bose-Einstein condensate dispersively coupled to a unidirectional ring cavity. A unique feature is that the population exchange among different modes of matter fields is accomplished via spin-exchange collisions. We show that the interplay between the atomic spin mixing and the cavity light field can lead to a strong matter-wave nonlinearity, making matter-wave bistability in a cavity at the single-photon level achievable.

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Detection of Fermi pairing via electromagnetically induced transparency

Lei Jiang, Han Pu, Weiping Zhang, and Hong Y. Ling

Phys. Rev. A 80, 033606 (2009) – Published September 9, 2009

Cited 3 times

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An optical spectroscopic method based on the principle of electromagnetically induced transparency (EIT) is proposed as quite a generic probing tool that provides valuable insights into the nature of Fermi paring in ultracold Fermi gases of two hyperfine states. This technique has the capability of allowing spectroscopic response to be determined in a nearly nondestructive manner and the whole spectrum may be obtained by scanning the probe-laser frequency faster than the lifetime of the sample without re-preparing the atomic sample repeatedly. A quasiparticle picture is constructed to facilitate a simple physical explanation of the pairing signature in the EIT spectra.

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Phase separation in a two-species atomic Bose-Einstein condensate with an interspecies Feshbach resonance

Lu Zhou, Jing Qian, Han Pu, Weiping Zhang, and Hong Y. Ling

Phys. Rev. A 78, 053612 (2008) – Published November 6, 2008

Cited 13 times

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We consider a mixture of two-species atomic Bose-Einstein condensates coupled to a bound molecular state at zero temperature via an interspecies Feshbach resonance. The interspecies Feshbach coupling precludes the possibility of doubly mixed phases while enables not only the pure molecular superfluid but also the pure atomic superfluids to exist as distinct phases. We show that this system is able to support a rich set of phase separations, including that between two distinct mixed atom-molecule phases. We pay particular attention to the effects of the Feschbach coupling and the particle collisions on the miscibility of this multicomponent condensate system.

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Goos-Hänchen-like shifts in atom optics

Jianhua Huang, Zhenglu Duan, Hong Y. Ling, and Weiping Zhang

Phys. Rev. A 77, 063608 (2008) – Published June 11, 2008

Cited 7 times

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We consider the propagation of a matter wave packet of two-level atoms through a square potential created by a super-Gaussian laser beam. We explore the matter wave analog of Goos-Hänchen shift within the framework of atom optics where the roles of atom and light are exchanged with respect to conventional optics. Using a vector theory, where atoms are treated as particles possessing two internal spin components, we show that not only large negative but also large positive Goos-Hänchen shifts can occur in the reflected atomic beam.

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Macroscopic Atom-Molecule Dark State and Its Collective Excitations in Fermionic Systems

Andrew Robertson, Lei Jiang, Han Pu, Weiping Zhang, and Hong Y. Ling

Phys. Rev. Lett. 99, 250404 (2007) – Published December 18, 2007

Cited 7 times

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We show that a robust macroscopic atom-molecule dark state can exist in fermionic systems, which represents a coherent superposition between the ground molecular Bose-Einstein condensates and the atomic BCS paired state. We take advantage of the tunability offered by external laser fields, and explore this superposition for demonstrating coherent oscillations between ground molecules and atom pairs. We interpret the oscillation frequencies in terms of the collective excitations of the dark state.

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Properties of a coupled two-species atom–heteronuclear-molecule condensate

Lu Zhou, Weiping Zhang, Hong Y. Ling, Lei Jiang, and Han Pu

Phys. Rev. A 75, 043603 (2007) – Published April 3, 2007

Cited 12 times

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We study the coherent association of a two-species atomic condensate into a condensate of heteronuclear diatomic molecules, using both a semiclassical treatment and a quantum mechanical approach. The differences and connections between the two approaches are examined. We show that, in this coupled nonlinear atom-molecule system, the population difference between the two atomic species plays a significant role in the ground-state stability properties as well as in coherent population oscillation dynamics.

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Adiabatic theorem for a condensate system in an atom-molecule dark state

Hong Y. Ling, Peter Maenner, Weiping Zhang, and Han Pu

Phys. Rev. A 75, 033615 (2007) – Published March 26, 2007

Cited 18 times

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We consider the adiabatic evolution of an atom-molecule dark state in a collisional two-color Raman photoassociation condensate system. By linking nonadiabaticity with the population growth in the collective excitations of the dark state, we develop an adiabatic theorem where we have consistently addressed the issues related to the Goldstone mode and the biorthonormality of the collective modes. We apply this theorem to specific examples to demonstrate its use in designing pulses that can optimize the yield of ground molecule production in the stimulated Raman adiabatic passage process.

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Adiabatic Condition for Nonlinear Systems

Han Pu, Peter Maenner, Weiping Zhang, and Hong Y. Ling

Phys. Rev. Lett. 98, 050406 (2007) – Published February 2, 2007

Cited 41 times

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The adiabatic approximation is an important concept in quantum mechanics. In linear systems, the adiabatic condition is derived with the help of the instantaneous eigenvalues and eigenstates of the Hamiltonian, a procedure that breaks down in the presence of nonlinearity. Using an explicit example relevant to photoassociation of atoms into diatomic molecules, we demonstrate that the proper way to derive the adiabatic condition for nonlinear mean-field (or classical) systems is through a linearization procedure, using which an analytic adiabatic condition is obtained for the nonlinear model under study.

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Molecular vortex generated from an atom-molecule dark state

H. Y. Ling, S. Yi, H. Pu, D. E. Grochowski, and Weiping Zhang

Phys. Rev. A 73, 053612 (2006) – Published May 26, 2006

Cited 4 times

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We consider a Raman photoassociation model in a field configuration in which a Gaussian and a first-order Laguerre Gaussian laser field are applied between the bound-bound and free-bound transitions, respectively. We show that such a configuration can lead to a coherent population trapping superposition of an atomic condensate and a ground molecular vortex of unit winding number. We develop stimulated Raman adiabatic passages that minimize the effect of mean-field shifts due to collisions, for optimal conversion of an atomic condensate into a ground molecular vortex.

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Coherent population trapping and dynamical instability in coupled atom-molecule condensates

H. Y. Ling, P. Maenner, and H. Pu

Phys. Rev. A 72, 013608 (2005) – Published July 18, 2005

Cited 10 times

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Coherent population trapping (CPT) is an important concept in many subfields of physics and chemistry. Here we analyze the collective excitation spectrum of the CPT states in a coupled atom-molecule condensate system. We find that collisions between particles can cause the CPT state to be dynamically unstable, which is a unique feature of the nonlinear system. We obtain a set of analytical criteria for determining the stability properties of the CPT state in the long-wavelength limit. We construct stability diagrams and provide a systematic classification of various instabilities according to collisional interaction strengths.

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Creating a Stable Molecular Condensate Using a Generalized Raman Adiabatic Passage Scheme

Hong Y. Ling, Han Pu, and Brian Seaman

Phys. Rev. Lett. 93, 250403 (2004) – Published December 15, 2004

Cited 59 times

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We study the Feshbach resonance assisted stimulated adiabatic passage of an effective coupling field for creating stable molecules from an atomic Bose condensate. By exploring the properties of the coherent population trapping state, we show that, contrary to the previous belief, mean-field shifts need not limit the conversion efficiency as long as one chooses an adiabatic passage route that compensates the collision mean-field phase shifts and avoids the dynamical unstable regime.

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Optical-cavity-assisted four-wave parametric amplification of atomic fields

Hong Y. Ling

Phys. Rev. A 65, 013608 (2001) – Published December 14, 2001

Cited 3 times

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We consider a system composed of a cavity field, a counterpropagating pump laser field, and a two-level Bose condensate travelling along a direction normal to the optical fields. We reduce the system, in the limit of first-order scattering approximation, to a four-wave parametric amplifier involving three momentum modes and an effective two-photon cavity mode. We treat this wave mixing as a multimode “laser” operation, and discuss the mode-locking condition under which these “laser” modes can be synchronized to operate in a continuous wave fashion. We derive the threshold lasing condition and discuss it in analogy with the Raman-anti-Stokes process in nonlinear optics. We develop a matrix formalism that enables the longitudinal spatial degree of freedom to be integrated analytically, leading to an efficient numerical algorithm for determining the steady states and their stabilities. Numerical examples will be provided and discussed. In particular, instability analysis seems to suggest Bose-Einstein condensate holds a great promise for nonlinear instability studies because of its unprecedented long interaction time with photons.

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Theory of a collective atomic recoil laser

H. Y. Ling, H. Pu, L. Baksmaty, and N. P. Bigelow

Phys. Rev. A 63, 053810 (2001) – Published April 17, 2001

Cited 8 times

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We perform a study of a collective atomic recoil laser (CARL) that goes beyond the initial growth period. The study is based on a theory that treats both internal and external degrees of atomic freedom quantum mechanically but regards the laser light as a classical field obeying Maxwell’s equations. We introduce the concepts of momentum families and diffraction groups and organize the matter wave equations in terms of diffraction groups. The steady-state lasing conditions are discussed in connection with the probe gain in the recoil-induced resonances. The nontrivial steady states and the linear stability analysis of the steady states are both carried out by the method of two-dimensional continued fractions. Both stable and unstable nontrivial steady states are calculated and discussed in the context of regarding the CARL as multiwave mixing involving many modes of matter waves and two optical fields.

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Effect of atomic recoil on the absorption spectrum of driven V-type atoms

Hong Y. Ling and Anthony Williams

Phys. Rev. A 60, 4812 (1999) – Published December 1, 1999

Cited 2 times

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A numerical method is developed for a V system driven by two counterpropagating laser fields in a momentum regime where a full quantum-mechanical treatment of the atomic variables is necessary. This method is based on a transformation by which integral equations, reduced from steady-state optical-Bloch-type equations involving the atomic center-of-mass momentum, can be transformed into inhomogeneous tridiagonal vector recurrence equations. The effect of the atomic recoil on the momentum distribution in the absence of the probe field, and, in particular, the absorption spectrum in a copropagating spectrum configuration is analyzed and discussed. Special attention is given to the Rayleigh resonance of subnatural linewidth.

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Several asymptotic subrecoil laser-cooling behaviors in arbitrary degenerate Λ systems

Hong Yuan Ling

Phys. Rev. A 59, 3714 (1999) – Published May 1, 1999

Cited 3 times

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Subrecoil cooling can be achieved in three-level Λ-type atoms subject to counterpropagating laser beams via velocity-selective coherent population trapping [A. Aspect et al., J. Opt. Soc. Am. B 6, 2112 (1989)]. This process leads to narrow peaks in the ground but a flat structure in the excited atomic momentum distributions. By taking advantage of this difference, we construct several analytical functions from which the main cooling features (with the exception of the scaling law about the fraction of subrecoil cooled atoms) can be approximated under arbitrary parameters. This method allows us to generalize the peak-momentum width from symmetric to arbitrary degenerate Λ systems, and to discuss analytically the small dependence of the momentum distributions on the laser detuning near the two-photon resonance.

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Electromagnetically induced grating: Homogeneously broadened medium

Hong Yuan Ling, Yong-Qing Li, and Min Xiao

Phys. Rev. A 57, 1338 (1998) – Published February 1, 1998

Cited 55 times

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A strong coupling standing wave, interacting with three-level Λ-type (or ladder-type) atoms, can diffract a weak probe field (propagating along a direction normal to the standing wave) into high-order diffractions, a phenomenon which we name electromagnetically induced grating (EIG). We develop in this work a theory for studying EIG in a homogeneously broadened medium consisting of three-level Λ-type atoms. We show that by taking advantage of the absorption and dispersion properties of electromagnetically induced transparency one can create an atomic grating that can effectively diffract light into the first-order direction.

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Coherent population trapping and electromagnetically induced transparency in multi-Zeeman-sublevel atoms

Hong Yuan Ling, Yong-Qing Li, and Min Xiao

Phys. Rev. A 53, 1014 (1996) – Published February 1, 1996

Cited 49 times

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We present a general formalism for studying the interaction between laser fields and degenerate-Zeeman-sublevel atoms correct up to the first order in the weak probe field. We derive from this theory the equations of motion for a Λ-type system involving S1/2, F=2P1/2, F′=1S1/2, F=1 transitions in 87Rb atoms. These equations are used to numerically investigate the coherent population trapping (CPT) schemes in the S1/2, F=2P1/2, F′=1 transition induced by a linearly polarized pumping field and the electromagnetically induced transparency exhibited in the weak probe spectrum in the S1/2, F=1P1/2, F′=1 transition. We discuss the effects of the CPT on the probe spectrum with and without the Doppler broadenings by comparing the probe spectrum derived from the real system with that derived from an ideal Λ-type system. We show that the atoms in the CPT states are shielded from interacting with the probe field while those in the absorbent states make contributions to the weak probe by the Raman anti-Stokes process, and the effect of the real system on the probe field becomes equivalent to the ideal Λ system only in the strong CPT parameter regime. © 1996 The American Physical Society.

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Theoretical investigation of phenomena in the closed Raman-driven four-level symmetrical model

Hong Yuan Ling

Phys. Rev. A 49, 2827 (1994) – Published April 1, 1994

Cited 4 times

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We construct a solution to the linear complex absorption coefficient for the closed Raman-driven four-level symmetrical model. We derive, from this solution, asymptotic expressions for the spectra around and away from the two-photon resonance in the absence as well as in the presence of the Doppler broadening. They are used for the derivations of analytical conditions and the discussion of the physical origins of various phenomena that do not appear in the traditional two-level system.

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