D. Meschede

Universität des Saarlandes, Saarbrücken, Saarland, Germany

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Publications (178)489.25 Total impact

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    ABSTRACT: We report on the observation of cooperative radiation of exactly two neutral atoms strongly coupled to the single mode field of an optical cavity in the good cavity limit. Monitoring the cavity output power, we observe super- and subradiant Rayleigh scattering into the cavity mode for certain relative distances between the two atoms. Surprisingly, due to cavity backaction onto the atoms, the cavity output power for superradiant scattering is almost equal to the single emitter case. These effects are quantitatively explained by a classical model as well as by a quantum mechanical model based on Dicke states. We extract information on the relative phases of the light fields at the atom positions and employ advanced cooling to reduce the jump rate between super- and subradiant configurations. Thereby we improve the control over the system to a level where the realization of two-atom entanglement schemes involving optical cavities becomes feasible.
    08/2014;
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    ABSTRACT: We experimentally realize an enhanced Raman control scheme for neutral atoms that features an intrinsic suppression of the two-photon carrier transition, but retains the sidebands which couple to the external degrees of freedom of the trapped atoms. This is achieved by trapping the atom at the node of a blue detuned standing wave dipole trap. We apply this method to perform resolved sideband cooling to the two-dimensional vibrational ground state and to coherently manipulate the atomic motion. The presented scheme requires minimal additional resources and can be applied to experiments with challenging optical access, as we demonstrate by our implementation for atoms strongly coupled to an optical cavity.
    06/2014;
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    ABSTRACT: When a physical object is in a quantum superposition, interference among the possible quantum paths affects the outcomes of a measurement. Gaining knowledge about the system with an intermediate measurement smears out, if not completely destroys, the resulting interference pattern. Based on this idea, Leggett and Garg formulated an inequality relating two-time correlation measurements, which establishes a quantitative criterion for discerning quantum superposition on a fundamental ground. Originally proposed to test realism of macroscopic physical objects, the inequality is here used to prove the non-classicality of the motion of a cesium atom, which propagates on a space-time discrete lattice. Making use of ideal negative measurements to test the atom's motion, we obtain a 6 sigma experimental violation of the Leggett-Garg inequality. From a broader perspective, our findings provide rigorous validation of the idea that quantum transport experiments cannot be interpreted in terms of classical trajectories.
    04/2014;
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    ABSTRACT: We demonstrate cooling of the motion of a single neutral atom confined by a dipole trap inside a high-finesse optical resonator. Cooling of the vibrational motion results from electromagnetically induced transparency (EIT)-like interference in an atomic Λ-type configuration, where one transition is strongly coupled to the cavity mode and the other is driven by an external control laser. Good qualitative agreement with the theoretical predictions is found for the explored parameter ranges. Further, we demonstrate EIT cooling of atoms in the dipole trap in free space, reaching the ground state of axial motion. By means of a direct comparison with the cooling inside the resonator, the role of the cavity becomes evident by an additional cooling resonance. These results pave the way towards a controlled interaction among atomic, photonic, and mechanical degrees of freedom.
    02/2014; 89(3).
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    ABSTRACT: We analyze the quantum jumps of an atom interacting with a cavity field. The strong atom-field interaction makes the cavity transmission depend on the time dependent atomic state, and we present a Hidden Markov Model description of the atomic state dynamics which is conditioned in a Bayesian manner on the detected signal. We suggest that small variations in the observed signal may be due to spatial motion of the atom within the cavity, and we represent the atomic system by a number of hidden states to account for both the small variations and the internal state jump dynamics. In our theory, the atomic state is determined in a Bayesian manner from the measurement data, and we present an iterative protocol, which determines both the atomic state and the model parameters. As a new element in the treatment of observed quantum systems, we employ a Bayesian approach that conditions the atomic state at time t on the data acquired both before and after t and we show that the state assignment by this approach is more decisive than the usual conditional quantum states, based on only earlier measurement data.
    12/2013; 89(4).
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    ABSTRACT: We present an in situ method to measure the birefringence of a single vacuum window by means of microwave spectroscopy on an ensemble of cold atoms. Stress-induced birefringence can cause an ellipticity in the polarization of an initially linearly polarized laser beam. The amount of ellipticity can be reconstructed by measuring the differential vector light shift of an atomic hyperfine transition. Measuring the ellipticity as a function of the linear polarization angle allows us to infer the amount of birefringence Δn at the level of 10(-8) and identify the orientation of the optical axes. The key benefit of this method is the ability to separately characterize each vacuum window, allowing the birefringence to be precisely compensated in existing vacuum apparatuses.
    The Review of scientific instruments 12/2013; 84(12):126103. · 1.52 Impact Factor
  • International Quantum Electronics Conference; 05/2013
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    ABSTRACT: We report on the experimental realization of electric quantum walks, which mimic the effect of an electric field on a charged particle in a lattice. Starting from a textbook implementation of discrete-time quantum walks, we introduce an extra operation in each step to implement the effect of the field. The recorded dynamics of such a quantum particle exhibits features closely related to Bloch oscillations and interband tunneling. In particular, we explore the regime of strong fields, demonstrating contrasting quantum behaviors: quantum resonances versus dynamical localization depending on whether the accumulated Bloch phase is a rational or irrational fraction of 2π.
    Physical Review Letters 05/2013; 110(19):190601. · 7.73 Impact Factor
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    ABSTRACT: Spin-dependent optical potentials allow us to use microwave radiation to manipulate the motional state of trapped neutral atoms (F\"orster et al. 2009 Phys. Rev. Lett. 103, 233001). Here, we discuss this method in greater detail, comparing it to the widely-employed Raman sideband coupling method. We provide a simplified model for sideband cooling in a spin-dependent potential, and we discuss it in terms of the generalized Lamb-Dicke parameter. Using a master equation formalism, we present a quantitative analysis of the cooling performance for our experiment, which can be generalized to other experimental settings. We additionally use microwave sideband transitions to engineer motional Fock states and coherent states, and we devise a technique for measuring the population distribution of the prepared states.
    Journal of Physics B Atomic Molecular and Optical Physics 02/2013; 46(10). · 2.03 Impact Factor
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    ABSTRACT: We report on controlled doping of an ultracold Rb gas with single neutral Cs impurity atoms. Elastic two-body collisions lead to a rapid thermalization of the impurity inside the Rb gas, representing the first realization of an ultracold gas doped with a precisely known number of impurity atoms interacting via s-wave collisions. Inelastic interactions are restricted to a single three-body recombination channel in a highly controlled and pure setting, which allows us to determine the Rb-Rb-Cs three-body loss rate with unprecedented precision. Our results pave the way for a coherently interacting hybrid system of individually controllable impurities in a quantum many-body system.
    Physical Review Letters 12/2012; 109(23):235301. · 7.73 Impact Factor
  • Dieter Meschede
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    ABSTRACT: Den diesjährigen Physik‐Nobelpreis erhielten zu gleichen Teilen Serge Haroche und David Wineland für ihre bahnbrechenden experimentellen Methoden, die es ermöglichen, individuelle Quantensysteme zu messen und zu manipulieren.
    Physik in unserer Zeit 11/2012; 43(6):272-273.
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    ABSTRACT: We experimentally demonstrate real-time feedback control of the joint spin-state of two neutral cesium atoms inside a high finesse optical cavity. The quantum states are discriminated by their different cavity transmission levels. A Bayesian update formalism is used to estimate state occupation probabilities as well as transition rates. We stabilize the balanced two-atom mixed state, which is deterministically inaccessible, via feedback control and find very good agreement with Monte Carlo simulations. On average, the feedback loop achieves near optimal conditions by steering the system to the target state marginally exceeding the time to retrieve information about its state.
    Physical Review Letters 10/2012; 109(17):173601. · 7.73 Impact Factor
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    U Wiedemann, W Alt, D Meschede
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    ABSTRACT: The internal state of organic photochromic spiropyran molecules adsorbed on optical microfibres is optically controlled and measured by state-dependent light absorption. Repeated switching between the states is achieved by exposure to the evanescent field of a few nanowatts of light guided in the microfibre. By adjusting the microfibre evanescent field strength the dynamic equilibrium state of the molecules is controlled. Time-resolved photoswitching dynamics are measured and modelled with a rate equation model. We also study how many times the photochromic system can be switched before undergoing significant photochemical degradation.
    Optics Express 06/2012; 20(12):12710-20. · 3.55 Impact Factor
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    ABSTRACT: Engineering quantum particle systems, such as quantum simulators and quantum cellular automata, relies on full coherent control of quantum paths at the single particle level. Here we present an atom interferometer operating with single trapped atoms, where single particle wave packets are controlled through spin-dependent potentials. The interferometer is constructed from a sequence of discrete operations based on a set of elementary building blocks, which permit composing arbitrary interferometer geometries in a digital manner. We use this modularity to devise a space-time analogue of the well-known spin echo technique, yielding insight into decoherence mechanisms. We also demonstrate mesoscopic delocalization of single atoms with a separation-to-localization ratio exceeding 500; this result suggests their utilization beyond quantum logic applications as nano-resolution quantum probes in precision measurements, being able to measure potential gradients with precision 5 x 10(-4) in units of gravitational acceleration g.
    Proceedings of the National Academy of Sciences 06/2012; 109(25):9770-4. · 9.81 Impact Factor
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    ABSTRACT: Ultracold gases doped with impurity atoms are promising hybrid systems that pave the way for investigation of a series of novel and interesting scenarios: They can be employed for studying polaron physics, the impurity atoms can act as coherent probes for the many-body system, and the coherent cooling of neutral atoms containing quantum information has been proposed. Here, we immerse single and few Cs atoms into an ultracold Rb cloud. Elastic collisions lead to rapid thermalization of both sub-systems, while inelastic collisions lead to a loss of Cs from the trap. When thermalized, the impurity atom is localized inside the Rb gas. The ultracold Rb gas remains effectively unaffected by the interaction with the Cs impurity atoms. The poster will present details of the experimental setup, sequence and data analysis needed to extract the interspecies scattering length and three-body loss coefficient from the thermalization dynamics and loss rates measured.
    06/2012;
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    ABSTRACT: We show that the presence of an interaction in the quantum walk of two atoms leads to the formation of a stable compound, a molecular state. The wave function of the molecule decays exponentially in the relative position of the two atoms; hence it constitutes a true bound state. Furthermore, for a certain class of interactions, we develop an effective theory and find that the dynamics of the molecule is described by a quantum walk in its own right. We propose a setup for the experimental realization as well as sketch the possibility to observe quasi-particle effects in quantum many-body systems.
    New Journal of Physics 01/2012; 14(7). · 4.06 Impact Factor
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    A Mawardi, S Hild, A Widera, D Meschede
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    ABSTRACT: We apply the Collins-Huygens integral to analytically describe propagation of a doughnut beam generated by a spiral phase plate. Measured beam profiles in free space and through an ABCD-lens system illustrate excellent agreement with theory. Applications range from the creation of optical beams with angular momentum to microscopy to trapping neutral atoms. The method extends to other beam shaping components, too.
    Optics Express 10/2011; 19(22):21205-10. · 3.55 Impact Factor
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    ABSTRACT: We report on the controlled insertion of individual Cs atoms into an ultracold Rb gas at about 400 nK. This requires to combine the techniques necessary for cooling, trapping and manipulating single laser cooled atoms around the Doppler temperature with an experiment to produce ultracold degenerate quantum gases. In our approach, both systems are prepared in separated traps and then combined. Our results pave the way for coherent interaction between a quantum gas and a single or few neutral atoms of another species.
    Applied Physics B 09/2011; · 1.78 Impact Factor
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    ABSTRACT: Coherent control and delocalization of individual atoms is a pivotal challenge in quantum technologies. As a new step on this road, we present an individual atom interferometer that is capable of splitting a trapped Cs atom by up to 10 μm, allowing us to measure potential gradients on the microscale. The atom is confined in a 1D optical lattice, which is capable of performing discrete state-dependent shifts to split the atom by the desired number of sites. We establish a high degree of control, as the initial atom position, vibrational state and spin state can all be prepared with above 95% fidelity. To unravel decoherence effects and phase influences, we have explored several basic interferometer geometries, among other things demonstrating a positional spin echo to cancel background effects. As a test case, an inertial force has been applied and successfully measured using the atomic phase. This will offer us a new tool to investigate the interaction between two atoms in a controlled model system.
    06/2011;
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    ABSTRACT: Using EIT, the refractive index of one atom inside a high finesse optical cavity is manipulated and the atomic motion has been cooled close to the axial ground state of the standing wave dipole trap.
    05/2011;

Publication Stats

3k Citations
489.25 Total Impact Points

Institutions

  • 2014
    • Universität des Saarlandes
      • Physikalische und Theoretische Chemie
      Saarbrücken, Saarland, Germany
  • 1970–2013
    • University of Bonn
      • Institute for Applied Physics
      Bonn, North Rhine-Westphalia, Germany
  • 2011
    • Universiti Malaysia Perlis
      • School of Microelectronic Engineering
      Kangar, Perlis, Malaysia
  • 1990–1992
    • Max Planck Institute of Quantum Optics
      Arching, Bavaria, Germany
  • 1987–1988
    • Yale University
      • Department of Physics
      New Haven, CT, United States