Showing papers on "Atomic coherence published in 2006"
TL;DR: In this paper, the authors analyzed hybrid absorptive-dispersive optical bistability and multistability behavior in a generic $N$-type atomic system driven by a degenerate probe field and a coherent coupling field by means of a unidirectional ring cavity.
Abstract: We analyze hybrid absorptive-dispersive optical bistability (OB) and multistability (OM) behavior in a generic $N$-type atomic system driven by a degenerate probe field and a coherent coupling field by means of a unidirectional ring cavity. We show that the OB can be controlled by adjusting the intensity and the detuning of the coupling field, and the OM can also be observed under the appropriate detuning. The influence of the atomic cooperation parameter on atomic OB behavior is also discussed.
231 citations
TL;DR: In this paper, the effect of spontaneously generated coherence on the Kerr nonlinearity of general three-level systems of three-dimensional (3D) systems was investigated, and it was found that the enhanced Kerr non-linearity can be attributed to the presence of an extra atomic coherence induced by the spontaneously generated Coherence.
Abstract: A theoretical investigation is carried out into the effect of spontaneously generated coherence on the Kerr nonlinearity of general three-level systems of $\ensuremath{\Lambda}$, ladder, and V-shape types. It is found, with spontaneously generated coherence present, that the Kerr nonlinearity can be clearly enhanced. In the $\ensuremath{\Lambda}$- and ladder-type systems, the maximal Kerr nonlinearity increases and at the same time enters the electromagnetically induced transparency window as the spontaneously generated coherence intensifies. As for the V-type system, the absorption property is significantly modified and therefore enhanced Kerr nonlinearity without absorption occurs for certain probe detunings. We attribute the enhancement of Kerr nonlinearity mainly to the presence of an extra atomic coherence induced by the spontaneously generated coherence.
201 citations
TL;DR: In this article, the authors demonstrate an atom localization scheme based on monitoring of the atomic coherences. And they show that this coherence has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of the atom coherence would localize the atom.
Abstract: We demonstrate an atom localization scheme based on monitoring of the atomic coherences. We consider atomic transitions in a Lambda configuration where the control field is a standing wave field. The probe field and the control field produce coherence between the two ground states. We show that this coherence has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of the atomic coherence would localize the atom. Interestingly enough the role of the cavity finesse is played by the ratio of the intensities of the pump and probe. This is in fact the reason for obtaining extreme subwavelenth localization. We suggest several methods to monitor the produced localization.
148 citations
TL;DR: In this article, an optical approach for excitation of nuclear spin states was proposed to reveal optical resonance linewidths at the hertz level with a good signal-to-noise ratio.
Abstract: Highest-resolution laser spectroscopy has generally been limited to single trapped ion systems because of the rapid decoherence that plagues neutral atom ensembles. Precision spectroscopy of ultracold neutral atoms confined in a trapping potential now shows superior optical coherence without any deleterious effects from motional degrees of freedom, revealing optical resonance linewidths at the hertz level with a good signal-to-noise ratio. The resonance quality factor of 2.4 × 1014 is the highest ever recovered in any form of coherent spectroscopy. The spectral resolution permits direct observation of the breaking of nuclear spin degeneracy for the 1S and 3P optical clock states of 87Sr under a small magnetic bias field. This optical approach for excitation of nuclear spin states allows an accurate measurement of the differential Lande g factor between 1S and 3P. The optical atomic coherence demonstrated for collective excitation of a large number of atoms will have a strong impact on quantum measurement and precision frequency metrology.
148 citations
TL;DR: A four-level atomic system with electromagnetically induced transparency with giant chi(3) and chi(5) susceptibilities of opposite signs will allow us to obtain multidimensional solitons and light condensates with surface tension properties analogous to those of usual liquids.
Abstract: We study a four-level atomic system with electromagnetically induced transparency with giant ${\ensuremath{\chi}}^{(3)}$ and ${\ensuremath{\chi}}^{(5)}$ susceptibilities of opposite signs. This system will allow us to obtain multidimensional solitons and light condensates with surface tension properties analogous to those of usual liquids.
115 citations
TL;DR: The coherent blue output is enhanced by several mechanisms, including stronger coupling to a larger fraction of the atomic population, operation at a detuning such that the vapor is nominally transparent to the 780 nm pump field, reduced losses owing to optical pumping, and optimal phase matching.
Abstract: We demonstrate production of continuous coherent blue laser light by using a five-level system in rubidium vapor. Two low-power lasers, at 780 and 776 nm, induce strong atomic coherence in the 5S-5P-5D states. The atoms decay to the 6P excited state, from which stimulated emission produces a coherent blue (420 nm) beam. We have coupled both ground-state hyperfine levels, effecting coherence between four levels. The coherent blue output is enhanced by several mechanisms, including stronger coupling to a larger fraction of the atomic population, operation at a detuning such that the vapor is nominally transparent to the 780 nm pump field, reduced losses owing to optical pumping, and optimal phase matching. We report experimental findings and compare them with results from a semiclassical Maxwell-Bloch model.
106 citations
TL;DR: In this article, the steady-state optical bistability behavior in a three-level A-type atomic system closed by a microwave field under the condition that the applied fields are in resonance with corresponding atomic transitions was investigated.
61 citations
TL;DR: The excitation and low-noise differential detection of a coherent population trapping (CPT) resonance with two modulated optical fields with orthogonal circular polarizations will enable nearly shot- noise-limited operation of atomic frequency references and magnetometers based on CPT.
Abstract: We demonstrate the excitation and low-noise differential detection of a coherent population trapping (CPT) resonance with two modulated optical fields with orthogonal circular polarizations. When a microwave phase delay of λ/4 is introduced in the optical path of one of the fields, the difference in the power transmitted through the cell in each polarization shows a narrow, dispersive resonance. The differential detection allows a high degree of suppression of laser-induced noise and will enable nearly shot-noise-limited operation of atomic frequency references and magnetometers based on CPT.
39 citations
TL;DR: In this article, an atomic optical bistable system with enhanced Kerr nonlinearity due to atomic coherence was used to demonstrate stochastic resonance (SR) in an optical ring cavity.
Abstract: Stochastic resonance (SR) is experimentally demonstrated in an atomic optical bistable system consisting of three-level atoms in $\ensuremath{\Lambda}$-type configuration confined in an optical ring cavity. The optical bistable system with enhanced Kerr nonlinearity due to atomic coherence is driven by a periodic signal and a Gaussian white noise source with variable amplitude, and displays an improved output signal-to-noise ratio, a characteristic signature of SR. The measured results match qualitatively with the theoretical predictions of the generic model for the SR phenomenon.
38 citations
TL;DR: In this paper, a single, tightly trapped atom is coupled by three laser fields in an $N$-shaped configuration of levels, whereby a $\Lambda$-type level system is weakly coupled to a metastable state.
Abstract: The spectroscopic properties of a single, tightly trapped atom are studied, when the electronic levels are coupled by three laser fields in an $N$-shaped configuration of levels, whereby a $\Lambda$-type level system is weakly coupled to a metastable state. We show that depending on the laser frequencies the response can be tuned from coherent population trapping at two-photon resonance to novel behaviour at three photon resonance, where the metastable state can get almost unit occupation in a wide range of parameters. For certain parameter regimes the system switches spontaneously between dissipative and coherent dynamics over long time scales.
28 citations
TL;DR: In this article, the probe gain with and without population inversion can be achieved with very weak incoherent pumping in a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field.
Abstract: In a three-level V-type atomic system without any external coherent driving, owing to the coherence that results from the vacuum of the radiation field, both the probe gain with and without population inversion can be achieved with very weak incoherent pumping. The gain is achieved in the absence of any external coherent driving field, so it is different from the gain without inversion in ordinary laser-driven schemes where a coherent driving field is necessary to create the coherence. The gain is also different from the conventional lasing gain because the population inversion is achieved via vacuum-induced coherence, which is dependent on the atomic coherence.
TL;DR: In this article, the authors analyse and numerically simulate the full many-body quantum dynamics of a spin-1 condensate in a single spatial mode approximation, and visualize the results of their simulations within the picture of irreducible tensor operators.
TL;DR: In this article, the entanglement of two identical two-level atoms in a single-mode thermal reservoir when these two atoms are initially prepared in coherent states was investigated, and it was discovered that the dynamical entagglement is greatly enhanced due to initial atomic coherence as compared with the case when the atoms are originally prepared in incoherent states.
Abstract: We have investigated the entanglement of two identical two-level atoms in a single-mode thermal reservoir when these two atoms are initially prepared in coherent states. It is discovered that the dynamical entanglement is greatly enhanced due to initial atomic coherence as compared with the case when the atoms are initially prepared in incoherent states. It is very valuable that we can manipulate the atomic entanglement by changing the relative phases and amplitudes of the polarized atoms.
TL;DR: In this article, the color-locked twin-noisy-field correlation effects in third-order nonlinear absorption and dispersion of ultrafast polarization beats were investigated, where the reference signal is another one-photon degenerate four-wave mixing signal, which propagates along the same optical path as the NDFWM signal.
Abstract: We investigate the color-locked twin-noisy-field correlation effects in third-order nonlinear absorption and dispersion of ultrafast polarization beats. We demonstrate a phase-sensitive method for studying the two-photon nondegenerate four-wave mixing (NDFWM) due to atomic coherence in a multilevel system. The reference signal is another one-photon degenerate four-wave-mixing signal, which propagates along the same optical path as the NDFWM signal. This method is used for studying the phase dispersion of the third-order susceptibility and for the optical heterodyne detection of the NDFWM signal. The third-order nonlinear response can be controlled and modified through the color-locked correlation of twin noisy fields.
01 Jan 2006
TL;DR: In this paper, the effect of spontaneously generated coherence on the Kerr nonlinearity of general three-level systems of Lambda, ladder, and V-shape types was investigated.
Abstract: A theoretical investigation is carried out into the effect of spontaneously generated coherence on the Kerr nonlinearity of general three-level systems of Lambda, ladder, and V-shape types. It is found, with spontaneously generated coherence present, that the Kerr nonlinearity can be clearly enhanced. In the Lambda- and ladder-type systems, the maximal Kerr nonlinearity increases and at the same time enters the electromagnetically induced transparency window as the spontaneously generated coherence intensifies. As for the V-type system, the absorption property is significantly modified and therefore enhanced Kerr nonlinearity without absorption occurs for certain probe detunings. We attribute the enhancement of Kerr nonlinearity mainly to the presence of an extra atomic coherence induced by the spontaneously generated coherence.
Dissertation•
01 Jan 2006
TL;DR: Ketterle et al. as mentioned in this paper studied the coherence properties of ultra-cold atomic gases, including a thermal cloud of atoms, a Bose-Einstein condensate and a fermion pair condensates.
Abstract: This thesis will discuss the study of coherence properties of ultra-cold atomic gases. The atomic systems investigated include a thermal cloud of atoms, a Bose-Einstein condensate and a fermion pair condensate. In each case, a different type of measurement is performed. However, all of the experiments share a common tool: an optical lattice which is used to probe these atomic gases. In the first case, we use an auto-correlation technique to study the interference pattern produced by a gas of atoms, slightly above the Bose-Einstein condensate transition temperature. A moving optical lattice is used to split and recombine the single particle atomic wavefunction. Analogous to a Young’s double slit experiment, we observe high contrast interference which is well described by the model which we develop. When we address only a velocity subset of the thermal sample, however, the contrast is enhanced and deviates from this model. In a second experiment we measure the coherence of a diatomic molecular gas, as well as the atomic Bose-Einstein condensate from which it was created. We use Bragg spectroscopy, in which atoms exchange photons with a moving optical lattice, transferring momentum to the atoms. This process can reveal the velocity distribution of the sample as energy and momentum are conserved only for a specific velocity class. Based on this measurement, we find that the atomic coherence is transferred directly to the molecular gas. We also discuss similar preliminary measurements performed on a fermion pair condensate in the BEC-BCS crossover. In a third experiment we study a fermion pair condensate into a 3D optical lattice. Such a system shares many similarities with electrons in solid materials which exhibit superconductivity, and can offer insight into mechanism which result in this behavior. We infer coherence from the sharp interference pattern observed in the expanding gas, after release. Finally, we study the abrupt onset of dissipation observed in a fermion pair condensate, as a function of velocity, in a moving optical lattice. We equate this threshold with the Landau critical velocity, and take measurements throughout the BEC-BCS crossover. The critical velocity is found to be maximum near unitarity, where the loss mechanism is predicted to crossover from phonon-like excitations to pair breaking. Thesis Supervisor: Wolfgang Ketterle Title: John D. MacAurthur Professor of Physics
TL;DR: In this paper, an effective four-level system around the D2 line, where the Rabi frequency of L1 exceeds that of L2, is experimentally investigated by fluorescent studies under the action of two driving fields L1 and L2.
Abstract: An effective four-level system around the D2 line
of 85Rb at room temperature, is experimentally investigated
by fluorescent studies
under the action of two driving fields L1 and L2.
This system exhibits unique features in fluorescence as a function of frequency
separation between L1 and L2. In particular, at two-photon resonance,
when the Rabi frequency of L1 exceeds that of L2,
signatures of Electromagnetically Induced Transperancy effect (EIT)
arising from the three-level Λ sub-system
is present as a sub-natural dip in fluorescence from the fourth level.
At comparable strengths of L1 and L2
the fluorescence features indicate a regime, where
the effects arising
from optical pumping and EIT effect due to ground hyperfine level coherence
coexist. We see in the coexistence regime, saturation
effects arising from difference frequency crossing (DFC) resonances and optical
pumping around the EIT window. At low strengths of L1, all signs of
coherence vanishes from the system and the fluorescent features result
from incoherent optical pumping through the
Autler-Townes split states of the excited state
hyperfine levels, which are split due to the stronger L2 laser.
The dominant role of the L1 laser in creating a robust transparency signal even
in the presence of an off-resonant excitation is brought out.
The results are supported by density matrix calculations.
01 Jan 2006
TL;DR: In this article, the authors describe a series of calculations and experiments that use atomic coherence for the generation of two-mode squeezed states of the electromagnetic field and propose a new quantumcommunication scheme that takes advantage of the properties of a twomode squeezed state.
Abstract: In this thesis we describe a series of calculations
and experiments that use atomic coherence for the generation of
two-mode squeezed states of the electromagnetic field. Atomic
coherence makes it possible to eliminate the problems of absorption
losses and spontaneous emission that have limited the amount of
squeezing obtained with atomic systems. Effects such as
electromagnetically induced transparency allow for efficient
generation of atomic coherence and are used as the basis for the
generation of squeezed states. We analyze the
use of a double-A configuration in order to combine a four-wave
mixing process and atomic coherence in a single system. The use of
this configuration makes it possible to eliminate absorption and
enhance the four-wave mixing process responsible for the generation
of a two-mode squeezed state. We implemented a
new detection technique, which we devised, based on the use of a
bichromatic local oscillator in a balanced heterodyne detection
scheme for the characterization of two-mode squeezed states. This
new detection technique makes it possible to characterize squeezed
states independently of the frequency separation between the modes.
In order to obtain the required phase-coherent
lasers, we designed and implemented a laser system that consists of
three stabilized external-cavity diode lasers. We obtained a system
with a residual phase noise of less than 0.04 rad². We studied
electromagnetically induced transparency in the Dl line of ⁸⁷Rb and
obtained a reduction in absorption of 92%. Experimentally, we
implemented the double-A configuration in the Dl line of ⁸⁷Rb in a
vapor cell. We were able to verify the presence of correlations
between the fields generated from the four-wave mixing process and
produced more than 10 decibels of phase-dependent noise modulation.
Finally, we propose a new quantum
communication scheme that takes advantage of the properties of a
two-mode squeezed state. This new scheme offers the possibility of
securely transmitting either a cryptographic key or a deterministic
message. We analyze the security of the scheme and find that it can
be verified with the use of the quantum correlations present in a
two-mode squeezed state.
TL;DR: In this article, the authors investigated the time evolution of the atomic dipole squeezing parameters of a Λ-type three-level atom interacting with a single-mode coherent optical field.
Abstract: By using the full quantum theory, we investigate the time evolution of the atomic dipole squeezing parameters of a Λ-type three-level atom interacting with a single-mode coherent optical field, and study the influence of the initial coherent-field intensity, the initial atomic coherence, the initial populations and energy splitting of the two lower atomic levels on the atomic dipole squeezing. The influence of a classical external driving field coupling to the atom on the atomic dipole squeezing is also explored at the end of the paper.
TL;DR: In this article, the dimensionless dynamic equations of two-photon laser with Λ atomic level configuration were derived by using the quantum Langevin equation method with the considerations of atomic coherence and injected classical fields.
Abstract: We derive the dimensionless dynamic equations of two-photon lasers with Λ atomic level configuration by using the quantum Langevin equation method with the considerations of atomic coherence and injected classical fields. Then we analyze the stability and the chaotic dynamics of the two-photon laser by calculating the bifurcation diagram and the maximum Lyapunov exponent (MLE). Our results show that the Lorenz strange attractors and one-focus strange attractors can exist in this system, and the chaos can be induced or inhibited by the injected classical fields via Hopf-bifurcations or crises, while the atomic coherence induces chaos via crises, and inhibit chaos via Hopf bifurcation or crises.
Patent•
11 Jan 2006
TL;DR: In this article, a method for implementing chromatic dispersion control by utilizing atomic coherence, belonging to the optical field, was proposed, which relates to a compensation technique of photochromatic dispersion.
Abstract: The present invention relates to a method for implementing chromatic dispersion control by utilizing atomic coherence, belonging to the optical field In particular, it relates to a compensation technique of photochromatic dispersion Said chromatic dispersion control system includes optical coupler, coherent pump, non-coherent pump and waveguide type device Said invention also provides the concrete structure of optical coupler and waveguide type device
TL;DR: In this article, a 7-level atom model was proposed, which takes into account two-photon coherence effects in saturation absorption spectroscopy and explained spectral change with laser intensity and some of crossover resonance lines.
Abstract: We propose a 7-level atom model, which takes into account two-photon coherence effects in saturation absorption spectroscopy. Using this model we explained spectral change with laser intensity and some of crossover resonance lines, which cannot be explained with Nakayama theory. The 7-level model consists of two upper levels and five lower levels, which account for polarization of both pump and probe beams in Zeeman sub levels. We compared our 7-level model with 4-level Nakayama theory for 5S - 5P transition line in Rb atoms. The results of the 7-level model calculation agree well the saturation absorption spectra data according to laser intensities.
10 Jul 2006
TL;DR: In this article, the authors show that the bandwidth for a conventional atomic vapour absorption frequency reference is limited by the atomic lifetime, and propose higher bandwidth frequency discrimination using atomic coherence mechanisms.
Abstract: We show that the bandwidth for a conventional atomic vapour absorption frequency reference is limited by the atomic lifetime, and propose higher bandwidth frequency discrimination using atomic coherence mechanisms.
TL;DR: In this article, the authors show that light fields propagating in atomic media with diamond level configuration exhibit two metastable behaviors of their relative phase, associated with separate types of atomic coherence and minimize dissipation.
Abstract: Light fields propagating in atomic media with diamond level configuration exhibit two metastable behaviors of their relative phase. These behaviours are associated with separate types of atomic coherence and minimize dissipation.
23 Jul 2006
TL;DR: In this paper, the influence of incoherent pumping on slow light propagation in rubidium atomic vapor was studied and it was shown that the pumping allowed to increase dynamic range of the system compared with the usual slow light system.
Abstract: We study influence of incoherent pumping on slow light propagation in rubidium atomic vapor. We show that the pumping allows to increase dynamic range of the system compared with the usual slow light system.
TL;DR: In this article, the cooperative behavior of spin decoherence and population transfer for a system of two driven multilevel atoms is studied, where the atoms are separated by a distance that is small compared to an optical wavelength.
Abstract: An ensemble of multilevel atoms is a good candidate for a quantum information storage device. The information is encrypted in the collective ground state atomic coherence, which, in the absence of external excitation, is decoupled from the vacuum and therefore decoherence free. However, in the process of manipulation of atoms with light pulses (writing, reading), one inadvertently introduces a coupling to the environment, i.e., a source of decoherence. The dissipation process is often treated as an independent process for each atom in the ensemble, an approach which fails at large atomic optical depths where cooperative effects must be taken into account. In this paper, the cooperative behavior of spin decoherence and population transfer for a system of two, driven multilevel atoms is studied. Not surprisingly, an enhancement in the decoherence rate is found, when the atoms are separated by a distance that is small compared to an optical wavelength; however, it is found that this rate increases even further for somewhat larger separations for atoms aligned along the direction of the driving field's propagation vector. A treatment of the cooperative modification of optical pumping rates and an effect of polarization swapping between atoms is also discussed, lending additional insight into the origin of the collective decay.