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Mon, 02 Jul 2001 00:00:00 +0200Mon, 02 Jul 2001 00:00:00 +0200Influence of center-of-mass correlations on spontaneous emission and Lamb shift in dense atomic gases
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1290
Abstract: Local field effects on the rate of spontaneous emission and Lamb shift in a dense gas of atoms are discussed taking into account correlations of atomic center-of-mass coordinates. For this the exact retarded propagator in the medium is calculated in independent scattering approximation and employing a virtual-cavity model. The resulting changes of the atomic polarizability lead to modi cations of the medium response which can be of the same order of magnitude but of opposite sign than those due to local field corrections of the dielectric function derived by Morice, Castin, and Dalibard [Phys.Rev.A 51, 3896 (1995)].M. Fleischhauerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1290Mon, 02 Jul 2001 00:00:00 +0200Dark-State Polaritons in Electromagnetically Induced Transparency
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1291
Abstract: We identify form-stable coupled excitations of light and matter ("dark-state polaritons") associated with the propagation of quantum fields in Electromagnetically Induced Transparency. The properties of the dark-state polaritons such as the group velocity are determined by the mixing angle between light and matter components and can be controlled by an external coherent field as the pulse propagates. In particular, light pulses can be decelerated and "trapped" in which case their shape and quantum state are mapped onto metastable collective states of matter. Possible applications of this reversible coherent-control technique are discussed.M. Fleischhauer; M. D. Lukinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1291Mon, 02 Jul 2001 00:00:00 +0200Quantum limit of optical magnetometry in the presence of ac-Stark shifts
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1292
Abstract: We analyze systematic (classical) and fundamental (quantum) limitations of the sensitivity of optical magnetometers resulting from ac-Stark shifts. We show that incontrast to absorption-based techniques, the signal reduction associated with classical broadening can be compensated in magnetometers based on phase measurements using electromagnetically induced transparency (EIT). However due to ac-Stark associated quantum noise the signal-to-noise ratio of EIT-based magnetometers attains a maximum value at a certain laser intensity. This value is independent on the quantum statistics of the light and defines a standard quantum limit of sensitivity. We demonstrate that an EIT-based optical magnetometer in Faraday configuration is the best candidate to achieve the highest sensitivity of magnetic field detection and give a detailed analysis of such a device.M. Fleischhauer; A. B. Matsko; M.O. Scullypreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1292Mon, 02 Jul 2001 00:00:00 +0200Entanglement of Atomic Ensembles by Trapping Correlated Photon States
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1293
Abstract: We describe a general technique that allows for an ideal transfer of quantum correlations between light fields and metastable states of matter. The technique is based on trapping quantum states of photons in coherently driven atomic media, in which the group velocity is adiabatically reduced to zero. We discuss possible applications such as quantum state memories, generation of squeezed atomic states, preparation of entangled atomic ensembles and quantum information processing.M. D. Lukin; S. F. Yelin; M. Fleischhauerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1293Mon, 02 Jul 2001 00:00:00 +0200How to Trap Photons? Storing Single-Photon Quantum States in Collective Atomic Excitations
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1294
Abstract: We show that it is possible to "store" quantum states of single-photon fields by mapping them onto collective meta-stable states of an optically dense, coherently driven medium inside an optical resonator. An adiabatic technique is suggested which allows to transfer non-classical correlations from traveling-wave single-photon wave-packets into atomic states and vise versa with nearly 100% efficiency. In contrast to previous approaches involving single atoms, the present technique does not require the strong coupling regime corresponding to high-Q micro-cavities. Instead, intracavity Electromagnetically Induced Transparency is used to achieve a strong coupling between the cavity mode and the atoms.M. Fleischhauer; S.F. Yelin; M. D. Lukinpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1294Mon, 02 Jul 2001 00:00:00 +0200Mirrorless oscillation based on resonantly enhanced 4-wave mixing: All-order analytic solutions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1295
Abstract: The phase transition to mirrorless oscillation in resonantly enhanced four-wave mixing in double-A systems are studied analytically for the ideal case of infinite lifetimes of ground-state coherences. The stationary susceptibilities are obtained in all orders of the generated fields and analytic solutions of the coupled nonlinear differential equations for the field amplitudes are derived and discussed.M. Fleischhauerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1295Mon, 02 Jul 2001 00:00:00 +0200Threshold and linewidth of a mirrorless parametric oscillator
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1296
Abstract: We analyze the above-threshold behavior of a mirrorless parametric oscillator based on resonantly enhanced four wave mixing in a coherently driven dense atomic vapor. It is shown that, in the ideal limit, an arbitrary small flux of pump photons is sufficient to reach the oscillator threshold. We demonstrate that due to the large group velocity delays associated with coherent media, an extremely narrow oscillator linewidth is possible, making a narrow-band source of non-classical radiation feasible.M. Fleischhauer; M.D. Lukin; A. B. Matsko; M. O. Scullypreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1296Mon, 02 Jul 2001 00:00:00 +0200Enhancement of Magneto-Optic Effects via Large Atomic Coherence
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1297
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.V. A. Sautenkov; M. D. Lukin; C. J. Bednar; G. R. Welch; M. Fleischhauer; V. L. Velichansky; M. O. Scullypreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1297Mon, 02 Jul 2001 00:00:00 +0200Quantum noise and correlations in resonantly enhanced wave mixing based on atomic coherence
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1299
Abstract: We investigate the quantum properties of fields generated by resonantly enhanced wave mixing based on atomic coherence in Raman systems. We show that such a process can be used for generation of pairs of Stokes and anti-Stokes fields with nearly perfect quantum correlations, yielding almost complete (i.e. 100%) squeezing without the use of a cavity. We discuss the extension of the wave mixing interactions into the domain of a few interacting light quanta.M. D. Lukin; A. B. Matsko; M. Fleischhauer; M. O. Scullypreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1299Mon, 02 Jul 2001 00:00:00 +0200Coherent population transfer beyond the adiabatic limit: generalized matched pulses and higher-order trapping states
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1301
Abstract: We show that the physical mechanism of population transfer in a 3-level system with a closed loop of coherent couplings (loop-STIRAP) is not equivalent to an adiabatic rotation of the dark-state of the Hamiltonian but coresponds to a rotation of a higher-order trapping state in a generalized adiabatic basis. The concept of generalized adiabatic basis sets is used as a constructive toolto design pulse sequences for stimulated Raman adiabatic passage (STIRAP) which give maximum population transfer also under conditions when the usual condition of adiabaticty is only poorly fulfilled. Under certain conditions for the pulses (generalized matched pulses) there exists a higher-order trapping state, which is an exact constant of motion and analytic solutions for the atomic dynamics can be derived.M. Fleischhauer; R. Unanyan; B.W. Shore; K. Bergmannpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1301Mon, 02 Jul 2001 00:00:00 +0200Interacting Dark Resonances: Interference Effects Induced by Coherently Altered Quantum Superpositions
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1304
Abstract: We predict the possibility of sharp, high-contrast resonances in the optical response of a broad class of systems, wherein interference effects are generated by coherent perturbation or interaction of dark states. The properties of these resonances can be manipulated to design a desired atomic response.M. D. Lukin; S.F. Yelin; M. Fleischhauer; M. O. Scullypreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1304Mon, 02 Jul 2001 00:00:00 +0200Thermal Properties of Interacting Bose Fields and Imaginary-Time Stochastic Differential Equations
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1305
Abstract: Matsubara Green's functions for interacting bosons are expressed as classical statistical averages corresponding to a linear imaginary-time stochastic differential equation. This makes direct numerical simulations applicable to the study of equilibrium quantum properties of bosons in the non-perturbative regime. To verify our results we discuss an oscillator with quartic anharmonicity as a prototype model for an interacting Bose gas. An analytic expression for the characteristic function in a thermal state is derived and a Higgs-type phase transition discussed, which occurs when the oscillator frequency becomes negative.L. I. Plimak; M. Fleischhauer; D. F. Wallspreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1305Mon, 02 Jul 2001 00:00:00 +0200Dipole Blockade and Quantum Information Processing in Mesoscopic Atomic Ensembles
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1287
Abstract: We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting "dipole blockade" can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as non-classical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.M.D. Lukin; M. Fleischhauer; R. Cote; L.M. Duan; D. Jaksch; J.I. Cirac; P. Zollerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1287Fri, 01 Jun 2001 00:00:00 +0200Quantum-field-theoretical techniques for stochastic representation of quantum problems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1286
Abstract: We describe quantum-field-theoretical (QFT) techniques for mapping quantum problems onto c-number stochastic problems. This approach yields results which are identical to phase-space techniques [C.W. Gardiner, Quantum Noise (1991)] when the latter result in a Fokker-Planck equation for a corresponding pseudo-probability distribution. If phase-space techniques do not result in a Fokker-Planck equation and hence fail to produce a stochastic representation, the QFT techniques nevertheless yield stochastic di erence equations in discretised time.L.I. Plimak; M. Fleischhauer; M.K. Olsen; M.J. Collettpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1286Fri, 01 Jun 2001 00:00:00 +0200On quantum logic operations based on photon-exchange interactions in an ensemble of non-interacting atoms
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1288
Abstract: The recently proposed idea to generate entanglement between photon states via exchange interactions in an ensemble of atoms (J. D. Franson and T. B. Pitman, Phys. Rev. A 60 , 917 (1999) and J. D. Franson et al., (quant- ph/9912121)) is discussed using an S -matix approach. It is shown that if the nonlinear response of the atoms is negligible and no additional atom-atom interactions are present, exchange interactions cannot produce entanglement between photons states in a process that returns the atoms to their initial state. Entanglement generation requires the presence of a nonlinear atomic response or atom-atom interactions.M. Fleischhauerpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1288Fri, 01 Jun 2001 00:00:00 +0200Diagram expansions in classical stochastic field theory / Diagram series and stochastic differential equations
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1217
We show that the solution to an arbitrary c-number stochastic differential equation (SDE) can be represented as a diagram series. Both the diagram rules and the properties of the graphical elements reflect causality properties of the SDE and this series is therefore called a causal diagram series. We also discuss the converse problem, i.e. how to construct an SDE of which a formal solution is a given causal diagram series. This then allows for a nonperturbative summation of the diagram series by solving this SDE, numerically or analytically.L.I. Plimak; M. Fleischhauer; M. J. Collettpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1217Tue, 15 May 2001 00:00:00 +0200Diagram expansions in classical stochastic field theory. I. Regularisations, stochastic calculus and causal Wick's theorem
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1216
Abstract: We aim to establish a link between path-integral formulations of quantum and classical field theories via diagram expansions. This link should result in an independent constructive characterisation of the measure in Feynman path integrals in terms of a stochastic differential equation (SDE) and also in the possibility of applying methods of quantum field theory to classical stochastic problems. As a first step we derive in the present paper a formal solution to an arbitrary c-number SDE in a form which coincides with that of Wick's theorem for interacting bosonic quantum fields. We show that the choice of stochastic calculus in the SDE may be regarded as a result of regularisation, which in turn removes ultraviolet divergences from the corresponding diagram series.L.I. Plimak; M. Fleischhauer; M.J. Collettpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1216Tue, 15 May 2001 00:00:00 +0200