Showing papers on "Atomic coherence published in 2009"
TL;DR: Using phase control between four- wave mixing (FWM) and six-wave mixing (SWM) channels in a four-level atomic system, temporal and spatial interferences between these two nonlinear optical processes are demonstrated.
Abstract: Using phase control between four-wave mixing (FWM) and six-wave mixing (SWM) channels in a four-level atomic system, we demonstrate temporal and spatial interferences between these two nonlinear optical processes. Efficient and coexisting FWM and SWM signals are produced in the same electromagnetically induced transparency window via atomic coherence. The temporal interference has a femtosecond time scale corresponding to the optical transition frequency. Such studies of intermixing between different order nonlinear optical processes with a controllable phase delay can have important applications in high-precision measurements, coherence quantum control, and quantum information processing.
208 citations
TL;DR: In this article, Bragg diffraction was employed to retrieve the stored optical information impressed into the atomic coherence by the incident light fields, which can be manipulated by an applied magnetic field and was able to observe collapses and revivals due to the rotation of the stored atomic Zeeman coherence for times longer than 15
Abstract: We report on the storage of orbital angular momentum of light in a cold ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The stored information can be manipulated by an applied magnetic field and we were able to observe collapses and revivals due to the rotation of the stored atomic Zeeman coherence for times longer than $15\text{ }\ensuremath{\mu}\text{s}$.
94 citations
TL;DR: In this paper, the power dependences of enhancement and suppression in four-wave mixing (FWM) processes were investigated. But the power dependence on the interference was not investigated.
Abstract: We report our observations of enhancement and suppression between two competing four-wave mixing (FWM) processes. The results show the evolution of the dressed effects (from pure enhancement into pure suppression) in the degenerate FWM processes. Moreover, due to induced atomic coherence in the system, there exist different interplays between these two FWM processes via different detuning parameters. In addition, the power dependences of enhancement and suppression are studied. Theoretical calculations are carried out, which are in good agreement with the experimental observations.
48 citations
TL;DR: In this paper, the dynamics of a two-level system driven by a strong off-resonant electromagnetic field was studied and an analytical solution for arbitrary pulse shape was derived.
Abstract: We study dynamics of a two-level system driven by a strong off-resonant electromagnetic field. We derive an analytical solution for arbitrary pulse shape. We discuss possible applications and presented experimental demonstration of the results obtained.
46 citations
TL;DR: In this article, the authors report experimental observations of spatial shift and splitting of four-wave mixing (FWM) signal beams induced by additional dressing laser beams, which are caused by the enhanced cross-Kerr nonlinearity due to atomic coherence in a two-level atomic system.
Abstract: We report our experimental observations of spatial shift and splitting of four-wave mixing (FWM) signal beams induced by additional dressing laser beams. These effects are caused by the enhanced cross-Kerr nonlinearity due to atomic coherence in a two-level atomic system. The spatial separation and number of the split FWM beams can both be controlled by the intensity of the dressing beam, the Kerr nonlinearity, and atomic density. Theoretical results agree quite well with the observations. Studies of such controlled beam splitting can be very useful in understanding spatial soliton formation and interactions, and in applications for spatial signal processing.
36 citations
TL;DR: In this article, an enhancement in Raman scattering in Rb atomic vapor due to the atomic coherence initially prepared by a weak write laser was demonstrated. But the effect of the coherence on the spatial distribution of the atomic spin coherence was not explored.
Abstract: We demonstrate experimentally an enhancement in Raman scattering in Rb atomic vapor due to the atomic coherence initially prepared by a weak write laser. We find that the enhanced Raman scattering depends on the spatial distribution of the atomic spin coherence and can be explained with a simple picture of three-wave mixing. This effect can in principle be used to have a light conversion efficiency near unity in Raman process. Such an enhanced Raman scattering may have practical applications in quantum information, nonlinear optics, and laser spectroscopy.
19 citations
TL;DR: In this article, the authors demonstrate the fast and accurate control of the evolution of collective atomic coherences in an erbium-doped solid using external electric fields, which is achieved by controlling the inhomogeneous broadening of the ion emitting at 1536 nm using an electric field gradient, thanks to the linear Stark effect.
Abstract: We demonstrate the fast and accurate control of the evolution of collective atomic coherences in an erbium-doped solid using external electric fields. This is achieved by controlling the inhomogeneous broadening of erbium ions emitting at 1536 nm using an electric field gradient, thanks to the linear Stark effect. The manipulation of atomic coherence is characterized with the collective spontaneous emission (optical free induction decay (FID)) emitted by the sample after an optical excitation, which does not require any previous preparation of the atoms. We show that controlled dephasing and rephasing of the atoms by the electric field result in collapses and revivals of the optical FID. Our results show that the use of external electric fields does not introduce any substantial decoherence and enables the manipulation of collective atomic coherence with a very high degree of precision on the timescale of tens of nanoseconds. This provides an interesting resource for photonic quantum state storage and quantum state manipulation.
19 citations
TL;DR: In this article, a scheme for achieving giant enhancement of the self-Kerr nonlinearity in a four-level Y-type atom with two highest nearly degenerate lying levels was proposed.
Abstract: We propose a new scheme for achieving giant enhancement of the self-Kerr nonlinearity in a four-level Y-type atom with two highest nearly degenerate lying levels. We have found that, owing to the quantum interference effect that originates from spontaneous emission from two closely lying levels, large Kerr nonlinearity can be achieved under appropriate conditions. In particular, in addition to the amplitudes, the phases of the applied fields also affect the Kerr nonlinearity. We attribute the enhancement of Kerr nonlinearity mainly to the presence of some extra atomic coherence terms induced by the spontaneously generated coherence. We present a physical understanding of our numerical results using analytical explanation.
19 citations
TL;DR: In this article, the quantum phase transitions between superfluid and Mott insulator states for ultracold bosons occupying two bands of an optical lattice were studied. And the two atomic states are resonantly coupled by a single cavity mode which mediates transitions between the two bosonic particle modes via absorption or emission of a cavity photon.
Abstract: We study the quantum phase transitions between superfluid and Mott insulator states for ultracold bosons occupying two bands of an optical lattice The two atomic states are resonantly coupled by a single cavity mode which mediates transitions between the two bosonic particle modes via absorption or emission of a cavity photon This coupling between the bands shifts the appearance of the Mott insulator phase towards deeper optical lattice potentials and stronger on-site interaction strength, as atomic coherence can build up via photon assisted tunneling in both bands Varying the intra and interband on-site interactions leads to several different atomic phase configurations There are even parameter regions where a mean field approach predicts concurrence of a Mott insulator state in one band, while atoms in the second band stay superfluid
15 citations
TL;DR: In this article, the negative refraction can be carried out with deeply depressing absorption and without simultaneously requiring both negative electric permittivity and magnetic permeability in an ideal situation where the two chirality coefficients have the same amplitude but the opposite phase.
Abstract: Electromagnetic chirality-induced negative refraction in a four-level atomic medium is investigated by initially preparing coherent states of the atom. We show that the negative refraction can be carried out with deeply depressing absorption and without simultaneously requiring both negative electric permittivity and magnetic permeability in an ideal situation where the two chirality coefficients have the same amplitude but the opposite phase.
14 citations
TL;DR: In this article, the coherence of spin-polarized atoms trapped in a light-shift-free one-dimensional optical lattice during their interaction with a clock laser on the 1S_0-^3P_0 transition was investigated.
Abstract: We investigated the coherence of spin-polarized ^{87}Sr atoms trapped in a light-shift-free one-dimensional optical lattice during their interaction with a clock laser on the ^1S_0-^3P_0 transition. Collapses and revivals appeared for more than 50 Rabi cycles, attributed to the thermal distribution of discrete vibrational states in the lattice potential. The population oscillation in the clock states lasted more than 1s, demonstrating high immunity from decoherence. This long atomic coherence suggests the feasibility of Pauli blocking of collisions in optical clock excitation.
TL;DR: In this article, a narrow (1 mm) coated cell geometry was employed to study hyperfine EIT and slow and stored light in warm R87b vapor, with results comparable to those in buffer gas cells and showing the promise of such cells for several applications.
Abstract: Alkali vapor cells with antirelaxation coated walls can have long atomic coherence times. However, using such coated cells in the hyperfine configuration for electromagnetically induced transparency (EIT) requires longitudinal atomic motion to be confined to less than the hyperfine wavelength. We employed a narrow (1 mm) coated cell geometry to study hyperfine EIT and slow and stored light in warm R87b vapor, with results comparable to those in buffer gas cells and showing the promise of such cells for several applications.
TL;DR: In this article, the coherence of spin-polarized 87 Sr atoms trapped in a light-shift-free one-dimensional optical lattice during their interaction with a clock laser on the 1 S 0 − 3 P 0 transition was investigated.
Abstract: We investigated the coherence of spin-polarized 87 Sr atoms trapped in a light-shift-free one-dimensional optical lattice during their interaction with a clock laser on the 1 S 0 – 3 P 0 transition. Collapses and revivals appeared for more than 50 Rabi cycles, attributed to the thermal distribution of discrete vibrational states in the lattice potential. The population oscillation in the clock states lasted more than 1 s, demonstrating high immunity from decoherence. This long atomic coherence suggests the feasibility of Pauli blocking of collisions in optical clock excitation.
TL;DR: In this paper, the steady-state optical bistability and optical multistability (OM) behavior in the quasi-Λ-type atomic system driven by a probe field and a coherent coupling field inside a unidirectional ring cavity are investigated.
Abstract: The steady-state optical bistability (OB) and optical multistability (OM) behavior in the quasi-Λ-type atomic system driven by a probe field and a coherent coupling field inside a unidirectional ring cavity are shown, and the effects of coupling-field detuning and coupling-field intensity on the OB and OM behavior are investigated. The transition from OB to OM or vice versa is found by varying the detuning of the coherent coupling field or by adjusting the intensity of the coupling field. The influence of the atomic cooperation parameter on the OM behavior is also discussed.
TL;DR: In this article, a short control pulse applied to the middle of an ultraslow light envelope results in coherence conversion between two ground states, causing both coherence depletion and recovery.
Abstract: Using an ultraslow light-based double-Λ-type configuration we demonstrate atomic coherence swing between two different frequencies in a nondegenerate four-wave mixing scheme. A short control pulse applied to the middle of an ultraslow light envelope results in coherence conversion between two ground states, causing both coherence depletion and recovery, resulting in a temporal hole and amplification in the ultraslow light envelope. This outcome holds potential for temporally and spatially localized coherence control of ultraslow light in such applications as a selective photon trap.
TL;DR: In this article, the authors investigate the generation and evolution of continuous-variable entanglement via an incoherent pump in a single-atom cavity electrodynamics (CQED) system.
Abstract: We investigate the generation and evolution of continuous-variable (CV) entanglement via an incoherent pump in a single-atom cavity electrodynamics (CQED) system. The atomic coherence in such a ? configuration is introduced by driving the lower two levels with a strong classical field of Rabi frequency ?m. It is shown that the intensity of the driving field can influence effectively the period of the entanglement between the two cavity modes.
TL;DR: In this article, the authors proposed a scheme of obtaining Ramsey fringes based on pulsed coherent optical information storage, which is free of light shifts as the interrogating process is separated from the optical pumping process.
Abstract: We propose a scheme of obtaining Ramsey fringes based on pulsed coherent optical information storage. Unlike the usual frequency references where the Ramsey fringes are obtained by detecting the population of a certain state, we get the Ramsey fringes by detecting the atomic coherence. The central line of the Ramsey fringes can be used as a frequency reference in an absorption-cell-based atomic frequency standard. This scheme is free of light shifts as the interrogating process is separated from the optical pumping process, and the cavity pulling effect is negligible due to the low $Q$ requirement. Encoding the Ramsey interference into the retrieval light pulse has the merit of high signal-to-noise ratio. This scheme is promising for building small, compact, and stable atomic clocks.
TL;DR: In this article, the authors proposed a scheme for robust writing and storage of optical phase information in populations of metastable states of the atoms with a tripod structure of levels by using frequency-chirped laser pulses.
Abstract: We propose a scheme for robust writing and storage of optical phase information in populations of metastable states of the atoms with a tripod structure of levels by using frequency-chirped laser pulses. The method provides much longer storage times compared with the schemes based on the collective atomic spin coherences. A negligible excitation of the atom provides immunity to decoherence induced by decay of the excited states. The method is robust against small-to-medium variations in the laser pulse intensity and speed of the chirp and, being insensitive to resonance conditions, it is effective both in homogeneously and inhomogeneously broadened media.
TL;DR: In this paper, the authors present an experimental study of the light transmission through an optical cavity coupled with coherently prepared cold Rb atoms, where the cavity transmission spectrum exhibits spectral peaks representing the cavity normal modes associated with the multi-atom vacuum Rabi splitting and the intra-cavity dark state manifested by the combined EIT effects of the absorption suppression and the steep normal dispersion.
Abstract: When a coherently prepared atomic medium is confined in an optical cavity, the atomic coherence and interference manifested by electromagnetically induced transparency (EIT) can be manipulated and enhanced by the collective atom–cavity coupling and the cavity feedback. We present an experimental study of the light transmission through an optical cavity coupled with coherently prepared cold Rb atoms. In the frequency domain, the cavity transmission spectrum exhibits spectral peaks representing the cavity normal modes associated with the multi-atom vacuum Rabi splitting and the intra-cavity dark state manifested by the combined EIT effects of the absorption suppression and the steep normal dispersion. In the time domain, a light pulse coupled into the cavity mode propagates with a slow group velocity and the propagation time delay is significantly increased by the cavity feedback.
TL;DR: In this paper, the evolution of coherence between two nondegenerate ground levels has been investigated in Rb atomic vapor using STIRAP and fractional StIRAP, a time-dependent coherence is prepared and indirectly monitored by the generated coherent Raman scattering signal proportional to the coherence.
TL;DR: In this paper, population transfer in a two-level system interacting with a strong off-resonant electromagnetic field was studied and it was shown that the effects of tunneling in an electric field enhances the probability of excitation.
Abstract: We study population transfer in a two-level system interacting with a strong off-resonant electromagnetic field. We show that the effects of tunneling in an electric field enhances the probability of excitation. We discuss the possible applications of results obtained to the generation of XUV radiation.
TL;DR: In this paper, the atomic coherence in a three-level Λ atom is studied, in which each optical transition is driven by a coherent field and the metastable states are coupled to each other via a microwave field.
Abstract: The atomic coherence in a three-level Λ atom is studied, in which each optical transition is driven by a coherent field and the metastable states are coupled to each other via a microwave field. It’s shown that the atomic coherence crucially depends on the relative phase delay between the envelopes of the amplitudes of the three coupling fields. In particular, when the phase delay is adjusted to 0 or π, the maximal atomic coherence arises, while the maximal atomic coherence doesn’t occur once the phase delay is changed to π/2. The maximal atomic coherence is attributed to the trapping of the population in the lower sublevels.
TL;DR: In this paper, an experimental implementation of stimulated Raman adiabatic passage (STIRAP), electromagnetically induced transparency (EIT) and the retrieval of light pulses in a Pr 3+ :Y 2 SiO 5 crystal was reported.
Abstract: We report on the experimental implementation of stimulated Raman adiabatic passage (STIRAP), electromagnetically induced transparency (EIT) and the retrieval of light pulses in a Pr 3+ :Y 2 SiO 5 crystal. We apply coherent, adiabatic processes to control population dynamics and atomic coherences in selected hyperfine levels of the praseodymium dopants in the crystal. Our data demonstrate efficient adiabatic population transfer by conventional STIRAP as well as by an alternative transfer process, i.e. b-STIRAP. Moreover, we investigate dark resonances, driven by EIT in a A-type and in a V-type level scheme. We apply EIT to create atomic coherences in Pr3 + :Y 2 SiO 5 . The persistent coherence is monitored by delayed retrieval of light pulses from the medium.
TL;DR: In this article, three paths of photon transition are coupled with three laser fields, and the effects of the laser field coupling with two upper levels on optical bistability are discussed.
Abstract: Optical bistability（OB） and optical multistability（OM） behaviour of ladder-type four-level atom in a unidirectional ring cavity driven by three laser fields is studied. Three paths of photon transition are coupled with the laser fields. In this case, the laser field Ω B coupling with two middle levels is very important. When the Ω B is increased, optical bistability threshold significantly decreases and optical multistability appears. The effects of the laser field coupling with two upper levels on optical bistability are also discussed. Furthermore, we analyze the effects of the detuning of probe field and atomic cooperation parameter on OB and OM.
14 Jun 2009
TL;DR: In this paper, self-induced transparency (SIT) is used to render a medium transparent to a resonant laser field, in which an optical pulse propagates in the medium such that an integer number of Rabi oscillations are performed.
Abstract: The ability to render a medium transparent to a resonant laser field opens a wide range of applications, from slow light and dark state polariton physics to light-matter interfaces. In atomic vapours at room temperature, Doppler broadening plays, in general, a negative role tending to reduce transparency. In a two-level (2L) system Doppler-free transparency can be achieved by means of self-induced transparency (SIT) (Fig.1(a,d)), which consists in preparing an optical pulse propagating in the medium such that an integer number of Rabi oscillations are performed [1]. Therefore, SIT requires a very precise temporal control of the Rabi frequency, i.e. the pulse area being an integer multiple of 2π. In three- (3L) and/or multi- level atomic systems, resonant transparency could be achieved by using induced atomic coherences, e.g., by means of the coherent population trapping (CPT) [2] and the electromagnetically induced transparency (EIT) phenomena [3] or via a double-STIRAP process [4]. In all these cases, the required two-photon (or Raman) resonance condition severely restricts the applications of the previous approaches to laser fields with nearly identical frequencies.
TL;DR: In this paper, the entanglement of a three-level atom in Λ configuration interacting with two quantized field modes by using logarithmic negativity was investigated, and the relationship of the atomic coherence and the entropy between two fields which are initially prepared in vacuum or thermal states was investigated.
Abstract: We investigate the entanglement of a three-level atom in Λ configuration interacting with two quantized field modes by using logarithmic negativity. Then, we study the relationship of the atomic coherence and the entanglement between two fields which are initially prepared in vacuum or thermal states. We find that if the two fields are prepared in thermal states, the atomic coherence can induce the entanglement between two thermal fields. However, there is no coherence-induced entanglement between two vacuum fields.
31 May 2009
TL;DR: In this paper, the photon logic gate is observed using ultra-low light, where the routing is based on atomic coherence enhanced by ultraslow light and the building block of the photon gate is photon routing phenomenon.
Abstract: Photon logic gates are observed using ultraslow light. The building block of the photon logic gate is photon routing phenomenon, where the routing is based on atomic coherence enhanced by ultraslow light.
14 Jun 2009
TL;DR: In this paper, the Trapped Rainbow method for stopping light is shown to be resilient to the presence of material losses, i.e. even with high material losses there are still guided electromagnetic modes, characterised by a real propagation constant and complex frequency which can assume a zero group velocity and be excited in a time domain experiment.
Abstract: It has recently been theoretically demonstrated that guided electromagnetic waves propagating along an adiabatically tapered negative-refractive-index metamaterial (MM) heterostructure can be considerably slowed down and stored by the Trapped-Rainbow method [1]. Here, we shall explain that, in principle, this method simultaneously allows for broad bandwidth operation (since it does not rely on group index resonances), large delay-bandwidth products (since a wave packet can be completely stopped and buffered indefinitely) and high, almost 100%, in/out-coupling efficiencies. By nature, the presented scheme invokes solid-state materials and, as such, is not subject to low-temperature or atomic coherence limitations. A wave analysis, which demonstrates the halting of a monochromatic field component travelling along the heterostructure, is followed by a pertinent ray analysis, which unmistakably illustrates the trapping of the associated light-ray and the formation of a double light-ray cone (‘optical clepsydra’) at the point where the ray is trapped. We shall explain that this method for stopping light is resilient to the presence of material losses, i.e. even in the presence of high material losses there are still guided electromagnetic modes, characterised by a real propagation constant and complex frequency which can assume a zero group velocity and be excited in a time-domain experiment.
01 Jan 2009
TL;DR: In this article, the effects of many-body Coulomb interactions on the optical response of Germanium nanocrystals (NCs) have been analyzed and the results indicate that Ge NCs can be used to generate optically and electrically controllable slow light.
Abstract: SLOW LIGHT IN GERMANIUM NANOCRYSTALS Umit Keles M.S. in Physics Advisor: Assoc. Prof. Dr. Ceyhun Bulutay August, 2009 The phenomena of quantum coherence has been applied with great success in the atomic systems. For optoelectronic applications the interest is inherently directed towards the semiconductor heterostructures. Large number of works have proposed and analyzed the atomic quantum coherence effects in the semiconductors. In this respect, nanocrystals (NCs) are very promising structures for seeking the quantum coherence phenomena due to their atomic-like electronic structure. Furthermore, their robust structure, integrability and larger excitonic lifetimes with respect to atomic systems makes them more promising candidates for the technological applications. Within an atomistic pseudopotential electronic structure framework, the optical Bloch equations (OBEs) originating from atomic coherence theory are derived and solved numerically for Ge NCs. The results are interpreted in the context of coherent population oscillations (CPO). Narrow dips are observed in the absorption profiles which corresponds to high dispersions within a transparency window and produce slow light. A systematic study of the size-scaling of slow-down factor with respect to NC diameter and controllable slow light by applying external Stark field are provided. The results indicate that Ge NCs can be used to generate optically and electrically controllable slow light. The many-body Coulomb interactions which underlie the quantum coherence and dephasing are of central importance in semiconductor quantum confined systems. The effects of many-body interactions on the optical response of Ge NCs have been analyzed. The semiconductor optical Bloch equations (SBEs) are derived in a semiclassical approach and the Coulomb correlations are included at the level of Hartree-Fock approximation.