Showing papers on "Atomic coherence published in 2000"

Resonant Nonlinear Optics in Phase-Coherent Media

Abstract: Publisher Summary This chapter reviews some recent theoretical and experimental studies on resonantly enhanced nonlinear interactions in phase-coherent media (“phaseonium”). Basic physics of resonant enhancement and applications such as efficient optical phase conjugation and nonlinear laser spectroscopy are discussed in the chapter. It suggests an efficient optical parametric oscillator based on population trapped atoms. Such an oscillator has very remarkable properties because it combines high efficiency with wide tunability. It illustrates those efficient nonlinear interactions in phase coherent media can be extended into domains involving just a few interacting light quanta at a time. This indicates that an entire new domain of quantum nonlinear optics is emerging from these studies. The chapter explores that unusually efficient frequency up-conversion using atomic coherence in a cascade system has been observed.

Enhancement of magneto-optic effects via large atomic coherence in optically dense media

Abstract: We utilize the generation of large atomic coherence to enhance the resonant nonlinear magneto-optic effect by several orders of magnitude, thereby eliminating power broadening and improving the fundamental signal-to-noise ratio. A proof-of-principle experiment is carried out in a dense vapor of Rb atoms. Detailed numerical calculations are in good agreement with the experimental results. Applications such as optical magnetometry or the search for violations of parity and time reversal symmetry are feasible.

Coherence properties of a continuous atom laser

Abstract: We investigate the coherence properties of an atomic beam evaporatively cooled in a magnetic guide, assuming thermal equilibrium in the quantum degenerate regime. The gas experiences two-dimensional, transverse Bose-Einstein condensation rather than a full three-dimensional condensation because of the very elongated geometry of the magnetic guide. First order and second order correlation functions of the atomic field are used to characterize the coherence properties of the gas along the axis of the guide. The coherence length of the gas is found to be much larger than the thermal de Broglie wavelength in the strongly quantum degenerate regime. Large intensity fluctuations present in the ideal Bose gas model are found to be strongly reduced by repulsive atomic interactions; this conclusion is obtained with a one-dimensional classical field approximation valid when the temperature of the gas is much higher than its chemical potential, k B T » |μ|.

Pancharatnam Phase of Two-Mode Optical Fields with Kerr Nonlinearity

Abstract: The Pancharatnam phase when an ideal cavity is filled with a Kerr-like medium and coupling is affected through a nondegenerate Raman two-photon process is studied. A careful investigation is made seeking exact results on the temporal evolution of atomic inversion and Pancharatnam phase. We invoke the mathematical notion of maximum variation of a function to construct a measure for Pancharatnam phase fluctuations. It is shown that Pancharatnam phase contains explicit information about the statistics of the field and atomic coherence, and is also shown that addition of the Kerr medium has an important effect on the properties of this phase. The results show that the effect of the Kerr medium changes the quasiperiod of the Pancharatnam phase evolution. The influence of Stark shift on the atomic inversion and the Pancharatnam phase in both presence and absence of the nonlinear medium is examined. General conclusions reached are illustrated by numerical results.

Collective effects in the self-interference of a single photon emitted by two atoms

Abstract: Collective effects in the spontaneous emission pattern of two identical two-level atoms a fixed distance apart and sharing initially a single excitation are investigated. It is shown that the interference can take place even when it is known for certain which atom is excited initially. This interference is due solely to the atomic coherence established through multiple photon absorptions and reemissions and will disappear if it is ignored. The interference patterns with and without collective effects are compared for symmetric and antisymmetric initial states. The dark center from an antisymmetric state is shown both analytically and numerically.

Quantum-state tomography using phase-sensitive amplification

Abstract: The phase-sensitive linear amplification has been exploited for the tomographic reconstruction of single as well as multimode entangled fields. For the phase-sensitive amplification of a single mode cavity field both the correlated emission laser (CEL) and the driven three-level atomic system are used as amplifiers. A CEL amplifier amplifies both the quadratures of the field equally but introduces an unequal amount of noise in them. In this amplifier, the added noise in one of the quadratures of the field is quenched at the expense of enhanced noise in the conjugate quadrature. The noise-free quadrature of the amplified field is measured by using a balanced homodyne detector (BHD). A one-to-one correspondence, in between the phase of the atomic coherence in CEL amplifier and the phase of the local oscillator (LO) used in the BHD, helps to record the noise-free quadrature of the field for a set of its phases. The measured quadrature distribution is then used to reconstruct the Wigner distribution of the field by using inverse Radon transformation. It is shown that in the limits of strong enough squeezing and sufficiently large gain the Wigner distribution of the initial field is recovered. This model has been applied to a Schrodinger-cat state and the Wigner function of its initial state is successfully reconstructed after its amplification through a two-photon CEL amplifier. In a driven three-level atomic system amplifier the atomic coherence in between the upper and the lower levels is produced by an external driving field. This system exhibits a range of interesting behaviour depending upon the strength of external driving field. For a weak driving field this system acts as a phase-insensitive amplifier whereas, it behaves as a perfect degenerate parametric amplifier at the other extreme of the driving field strength. In the parametric limit of its operation, this system quenches added noise from both the quadratures of the field however, one of the quadratures gets amplification at the cost of deamplification in the conjugate one. The amplified field quadrature is measured by using a BHD. A one-to-one correspondence in between the phase of the external driving field and the phase of the LO, helps to record the field quadrature with optimum gain over a set of its phases. The measured quadrature distribution is then used to reconstruct the Wigner function of the original field. This model is also applied to reconstruct the Wigner function of a Schrodinger-cat state. For a multimode entangled state of a cavity field two cases of interest are discussed. In the first case, the cavity modes are defined in terms of different frequency components and in the other case, the field modes consist of two orthogonal polarization states. In both these cases the cavity field is amplified by using CEL amplifiers. The measurement of the amplified field, consisting of different frequency components, is realized by seperating it out into its frequency components such that each frequency component is measured at a seperate set of BHD. However, for the measurement of a bimode field, having the same frequency, a single set of BHD is quite suffice. In this case the amplified field is first passed through a polarizer and then through a phase-shifter before its detection through a BHD. This arrangement helps to record the joint quadrature distribution of the bimode field. The measured quadrature distributions of both these fields are then used to reconstruct the Wigner functions of the fields. It is shown that for sufficiently large squeezing and for large enough gain in each mode of the field the Wigner functions of the initial states are successfully recovered.

Inhomogeneous broadening-dependent spectral features in a four-level atomic system

Abstract: New spectral features in an inhomogeneously broadened N-type four-level atomic system are analyzed and discussed. The atomic-level scheme uses an incoherent pumping rate in place of the incoherent recycling pump. We show that the gain profile includes an extra dip that appears only in the Doppler-broadened case. The dependence of this feature on various parameters, as well as consequences for the dispersion, are explored theoretically. For certain combinations of temperature and incoherent pump rate, this gain is shown to be independent of temperature fluctuations.

Nonlinear manipulation and control of matter waves

Abstract: This paper reviews some of our recent results in nonlinear atom optics. In addition to nonlinear wave-mixing between matter waves, we also discuss the dynamical interplay between optical and matter waves. This new paradigm, which is now within experimental reach, has the potential to impact a number of fields of physics, including the manipulation and applications of atomic coherence, and the preparation of quantum entanglement between microscopic and macroscopic systems. Possible applications include quantum information processing, matter-wave holography, and nanofabrication.

Self-Organized Formation of Atomic Coherence via Photon Exchange in a Coupled Atom-Photon System

Abstract: The formation of the atomic coherence via a photon field has been considered to play an essential role in the laser action. The importance of the formation has been also recognized from the viewpoint of cavity QED. This paper analyzes quantum mechanical dynamics of a self-organized formation of coherence between atoms and photon field. We solved an equation of a reduced density operator for a quantum laser model with plural atoms by using coherent states and orthogonal polynomials, and obtained a solution in a continued fraction form. We numerically evaluate time evolution of averaged physical quantities and quasi-probability density of photon field. Under an appropriate condition for laser oscillation, time evolution of an average of induced atomic dipole moments shows a co-operative phenomenon. Numerical evaluation of the quasi-probability density of a photon field reveals that a coherently more stabilized and stronger photon field emerges as the number of atoms increases. To our knowledge, this is the ...

Correlation of matched electric fields in four-level atoms via electromagnetically induced transparency

Abstract: We investigated the matching of two continuous fields in a closed four-level system quantum mechanically. When the atomic coherence is prepared in the dressed state by two strong external coupling fields, fluctuations of phase and amplitude between the two probe fields are selectively absorbed, while these fields are mainly transparent in the media. Such selective absorption establishes the phase and amplitude correlation between the two weak probe fields over a wide range of frequencies. However, the correlation remains limited by the standard quantum limit, because of the addition of the anti-phase atomic noise during the four-wave mixing process.

Freezing Light via atomic coherence

Abstract: We prove that it is possible to freeze a light pulse (ie, to bring it to a full stop) or even to make its group velocity negative in a coherently driven Doppler broadened atomic medium via electromagnetically induced transparency (EIT) This remarkable phenomenon of the ultra-slow EIT polariton is based on the spatial dispersion of the refraction index $n(\w,k)$, ie, its wavenumber dependence, which is due to atomic motion and provides a negative contribution to the group velocity This is related to, but qualitatively different from, the recently observed light slowing caused by large temporal (frequency) dispersion

Coherent control of the polarization of optical pulses using electromagnetically induced transparency

Abstract: Electromagnetically induced transparency (EIT) refers to a phenomenon, whereby the optically resonant transition is rendered nearly transparent by applying a strong coupling laser field. The mechanism of EIT is usually explained in terms of quantum coherence or quantum interference. This EIT has attracted increasing interest because absorption associated with nonlinear optical processes can be removed. In the typical three-level /spl lambda/-system, which includes the ground state and the metastable state, when the atomic population is prepared in the superposition of the states by the coupling fields, the optical response of the media to the probe field is significantly modified. Since this is a coherent control of an electric field by another field via the atomic coherence, several schemes to control light coherently have been suggested. We propose an optical coherent control scheme of the polarization of optical pulses using the EIT quantum coherence, and numerically study its applicability to fast optical switching.

Atomic coherence-state phase conjugation in optical coherent transients

Abstract: Summary form only given. Time-domain four- and six-wave mixing has been demonstrated as an important input scheme for proposed spatial-spectral holographic processing devices. Optimizing the design of these devices requires an understanding of the optical coherent transient phenomena resulting from time-domain wave mixing. In this paper, we show that a particular set of six-wave mixing signals can be directly related to the coherence-state pathways of time-domain four-wave mixing.

Freezing Light via Atomic Coherence

Abstract: We prove that it is possible to freeze a light pulse (i.e., to bring it to a full stop) or even to make its group velocity negative in a coherently driven Doppler broadened atomic medium via electromagnetically induced transparency (EIT). This remarkable phenomenon of the ultra-slow EIT polariton is based on the spatial dispersion of the refraction index $n(\w,k)$, i.e., its wavenumber dependence, which is due to atomic motion and provides a negative contribution to the group velocity. This is related to, but qualitatively different from, the recently observed light slowing caused by large temporal (frequency) dispersion.

Atom-cavity dynamics in the limit of ultraslow atomic decoherence

Abstract: Summary form only given. An underlying premise of quantum computing is the preservation of system coherence over long time scales. Here, we report studies of atom-cavity dynamics wherein behavior observed is distinctively related to the ultraslow atomic decoherence found in one such system. In our experiment, the atomic decoherence time is four orders of magnitude longer than the empty-cavity lifetime, making the atomic coherence the longest-lived system parameter. The phenomenon we observe here may be loosely thought of as cavity-mediated self-driven optical nutation, i.e., optical nutation driven by the active atoms own coherent emission into the cavity mode.