Electro-optic quantum memory for light using two-level atoms

We present a simple quantum memory scheme that allows for the storage of a light field in an ensemble of two-level atoms. The technique is analogous to the NMR gradient echo for which the imprinting and recalling of the input field are performed by controlling a linearly varying broadening. Our protocol is perfectly efficient in the limit of high optical depths and the output pulse is emitted in the forward direction. We provide a numerical analysis of the protocol together with an experiment performed in a solid state system. In close agreement with our model, the experiment shows a total efficiency of up to 15%, and a recall efficiency of 26%. We suggest simple realizable improvements for the experiment to surpass the no-cloning limit.     

The polarization of light emitted from sputtered Mg atoms

The polarization fraction of light emitted from Mg atoms excited during bombardment of the Mg polycrystalline target by low-energy Ne⁺ ions has been measured. Taking into account the results, a possible mechanism of excitation of sputtered atoms is suggested.     

Generation of light using two-level atoms with initial coherence

The Fokker-Planck equation for the Glauber quasi-probability is derived, which describes one-photon generation of light in lasers and micromasers using atoms with initial coherence. Stationary lasing and masing conditions are analyzed. In particular, the case of an inversionless transition is considered. The line shape and the photon statistics are found. The field state for lasing on an inversionless transition is found to be coherent.     

A theory of two-photon light generation involving inversionless two-level atoms

We propose a theory that makes it possible to examine both laser and micromaser two-photon light generation. The theory is based on the Lamb-Scully model, in which two-level atoms have initial coherence. Such an initial state allows for light generation involving atoms without inversion or even atoms with negative population inversion in the transition. We analyze the conditions needed for the emergence of squeezed states of the light field. We also show that the photon statistics in lasing is always classical but that there appears a state of the field squeezed in the phase with maximum photodetection shot-noise suppression. For a micromaser we find a regime where sub-Poisson light with a shot-noise suppression level of 60% is realized in an inversionless transition. In another regime, a squeezed state that produces 75% suppression of noise can be generated. Zh. éksp. Teor. Fiz. 115, 1605–1618 (May 1999)     

Dependence of phase dynamics of light interacting with two-level atoms on the initial state of atoms

We have studied the phase properties of initially coherent light interacting with two identical two-level atoms using the Hermitian phase operator of Pegg and Barnett. The results show that, in a certain initial state of the atoms, the field would, to a certain extent, preserve its order in phase, even for a long interaction time with the two atoms.     

Measuring speed of the light emitted by an ultrarelativistic source

The velocity of the light pulse emitted by an ultrarelativistic electron bunch is directly measured. The measured velocity is within 0.3% of the standard speed of light in a vacuum. The result can be considered as the most direct experimental confirmation of the second postulate of special relativity.     

From quantum light emitted by single molecule to classical light emitted by molecular ensemble

Fluorescence from an ensemble of noninteracting molecules excited by continuous laser radiation is considered as a glow of M individual molecules. The expression that governs the autocorrelation function (ACF) of fluorescence from M molecules is derived based on the theoretical expression that governs the ACF of fluorescence from a single-molecule. Fluctuations of blinking fluorescence and its statistical properties are analyzed using a computer simulation. The results of statistical analysis of the computer experiment are in good agreement with the derived formula that governs the ACF of fluorescence from several molecules.     

Atomic squeezing in assembly of two two-level atoms interacting with a single mode coherent radiation

Saito and Ueda [Phys. Rev. A 59, 3959 (1999)] studied atomic and radiation squeezing in interaction of a single mode coherent state of radiation with two excited two-level atoms, using the Jaynes Cummings Hamiltonian. They considered α real and studied squeezing of the Dicke operator S_x using the Kitagawa-Ueda criterion for squeezing and coupling times less than or nearly equal to . We obtain results to all orders in coupling time for atoms, which are initially in (i) fully excited, (ii) superradiant or in (iii) ground states and obtain more general results. We use our recently reported criterion for atomic squeezing, of which the Kitagawa-Ueda criterion is a special case, and obtain a much stronger (nearly 95%) atomic squeezing than that (nearly 1.1%) reported by Saito and Ueda.     

Controlling light by light with three-level atoms inside an optical cavity

We present our experimental demonstration of controlling the cavity output intensity of one laser beam with the intensity of another laser beam in a composite system consisting of a collection of three-level ?-type rubidium atoms and an optical ring cavity. When the intensity of the controlling beam is modulated with a square waveform, the cavity output power switches on and off (with a distinction ratio better than 20:1) between two steady-state values. This all-optical switching effect is the result of combined absorption and enhanced Kerr nonlinearity near resonance in such three-level atomic systems because of atomic coherence and can find applications in optical communication and optical computation.     

Simultaneous jumps in two two-level atoms

We demonstrate the importance of collective behaviour in two identical two-level atoms. When the atoms become very close together a cascade three-level atom analysis can be adopted to show the increasing possibility of simultaneous jumps. Due to the dipole-dipole interaction the intermediate one-atom excited state is detuned by a large amount when the atoms are close together but leaving the upper two-atom excited state in two-photon resonance. The relative importance of multiple jumps compared with stepwise independent jumps is then changed dramatically.     

Modified optical bloch equations in nonlocal systems of two-level atoms interacting with ultrashort light pulses

Modified optical Bloch equations for two-level atoms in the radiation field with the complex polarization vector, the complex amplitude, and the complex wave vector are derived. A specific case is considered in which a field of this kind acts on a separate atom of a nonlocal atomic system. The solution of the modified equations for the interaction of atoms with ultrashort light pulses is obtained.     

两纠缠原子与相干态光场相互作用过程中光场的量子特性

采用时间演化算符和数值计算方法,研究了两全同二能级纠缠原子与相干态光场相互作用过程中光场的量子特性,结果表明:两原子初始纠缠度和相干态光场强度对系统光场的二阶相干性质和压缩效应有很大的影响.     

存在偶极间相互作用的两能级原子的消相干

两个两能级原子置于外部环境(热库)中,当计及原子偶极间的相互作用时,通过研究两个原子约化密度矩阵,分析原子状态消相干规律。     

Scattering of atoms by light

This review discusses the latest theoretical and experimental achievements in the resonant light pressure acting on the translational motion of atoms. Alongside with the effects due to the spontaneous light pressure (atomic deflection, velocity bunching, cooling), various manifestations of the effects of induced light pressure are considered in detail. This paper provides the theory and experiments of atoms scattering by a standing light wave under the conditions of coherent and non-coherent interaction, diffraction and interference of atomic beams. The problems where atomic motion along two trajectories and Landau-Zener transitions between them are essential, are studied. The kinetic phenomena (scattering, cooling, channeling) due to the motion of the particles exposed to gradient force and also friction and diffusion caused by spontaneous emission are considered. The influence of the recoil effect under spontaneous emission of atoms on non-linear polarization phenomena is discussed.     

The decay dynamics of a slab of two-level atoms excited by an ultrashort resonant pulse

The decay dynamics of a slab of two-level atoms excited by an ultrashort resonant pulse are analyzed by means of the eigenmodes determined by the interaction of the resonance with the slab geometry. The node structure in the spatio-temporal excited atom distribution and the forward-backward asymmetry are identified with the decays of individual modes and with interference between adjacent modes.     

Polarization analysis of the light emitted by an optically pumped3He gas

Optical measurements of the nuclear polarizationM of an optically pumped pure³He gas have been performed. They consist in monitoring the circular polarization of various helium lines emitted by the discharge. We have demonstrated the possibility to use the orange line (587.5 nm) to measureM and we have calibrated this technique over the pressure range 0.4–6.5 Torr. The circular polarization of the light has been analyzed using a new device which includes a static polarimeter and photodiodes as light sensors. The intensity of the discharge was modulated and the detection was made at the frequency of modulation.Laboratoire associé au Centre National de la Recherche Scientifique et a l'Université P. M. Curie     

Decoherence in a system of many two-level atoms

I show that the decoherence in a system of degenerate two-level atoms interacting with a bosonic heat bath is for any number of atoms governed by a generalized Hamming distance (called "decoherence metric") between the superposed quantum states, with a time-dependent metric tensor that is specific for the heat bath. The decoherence metric allows for the complete characterization of the decoherence of all possible superpositions of many-particle states, and can be applied to minimize the overall decoherence in a quantum memory. For qubits which are far apart, the decoherence is given by a function describing single-qubit decoherence times the standard Hamming distance. I apply the theory to cold atoms in an optical lattice interacting with blackbody radiation.     

Stimulated emission by two-level atoms pumped to the upper level

We analyze the quantum properties of the light generated by a two-level laser in which the two-level atoms available in a closed cavity are pumped to the upper level by means of electron bombardment. We carry out our analysis by putting the noise operators associated with a vacuum reservoir in normal order. The normal ordering of the noise operators leads to normally-ordered quadrature and photon-number variance. It so turns out that the light generated by the two-level laser operating well above threshold is coherent and the light generated by the same laser operating at threshold is chaotic.     

Coherent backscattering of nonmonochromatic light by an ensemble of cold atoms

The coherent backscattering of light by an ensemble of cold atoms in a magneto-optical trap is studied theoretically. The effect of the width and shape of the incident light spectrum on the enhancement factor and total intensity of the backscattered light is analyzed. The calculations are performed for ⁸⁵Rb atoms with allowance for the entire hyperfine and Zeeman structure of the ground and excited states of the atoms, spatial inhomogeneity of the atomic cloud, and motion of the atoms.