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Quantum technologies

Dieter Meschede's research group
Home AMO physics colloquia
  • Prof. Philipp Treutlein

  • Invited speaker: Prof. Philipp Treutlein
    Affiliation: Universität Basel
    Title: Quantum Metrology With Ultracold Atoms On A Chip
    Time and room: 17:15, lecture hall IAP
    Abstract: Atom chips provide a versatile quantum laboratory for experiments with ultracold atomic gases. Electromagnetic fields from microstructured wires and electrodes are used to cool, trap, and coherently manipulate the quantum state of the atoms. This enables chip-based atomic clocks and interferometers, which combine high precision with a compact and robust setup. In such an interferometer, we generate spin-squeezed states of the atoms through the "one-axis twisting model" first described by Kitagawa and Ueda in 1993. These multi-particle entangled states are a useful resource for quantum metrology, as they allow one to overcome the standard quantum limit of interferometric measurement.

    High-resolution imaging of electromagnetic fields is a metrology task for which atom chips are particularly well-suited. We have used ultracold atoms for microwave field imaging near on-chip waveguides. This novel technique is of interest for testing and optimizing integrated microwave circuits, which are at the heart of modern communication technology.

    M. F. Riedel, P. Böhi, Yun Li, T. W. Hänsch, A. Sinatra, and P. Treutlein, Nature 464, 1170 (2010).
    R. Schmied and P. Treutlein, New J. Phys. 13, 065019 (2011).
    P. Böhi, M. F. Riedel, T. W. Hänsch, and P. Treutlein, Appl. Phys. Lett. 97, 051101 (2010).

  • Prof. Serge Haroche

  • Invited speaker: Prof. Serge Haroche
    Affiliation: Collège de France und Ecole Normale Supérieure, Paris
    Title: Real Time Quantum Feedback Control Of Non-Classical Field States In A Cavity
    Time and room: 13:15, lecture hall IAP
    Abstract: In our Cavity Quantum Electrodynamics experiments, we use a beam of Rydberg atoms to manipulate and probe non-destructively microwave photons trapped in a very high Q superconducting cavity. In recent years, we have realized ideal quantum non-demolition (QND) measurements of photon numbers, observed the radiation quantum jumps due to cavity relaxation and prepared non-classical fields such as Fock and Schrödinger cat states. Combining QND photon counting with a homodyne mixing method, we have reconstructed the Wigner functions of these non-classical states and, by taking snapshots of these functions at increasing times, obtained movies of the decoherence process.

    The next step in this research program was to demonstrate ways to protect these non-classical states against decoherence. One natural method is to implement a procedure analogous to the feedback strategies used to stabilize complex systems in classical physics. A probe measures the system state, a controller determines the action leading it towards the chosen operating point and an actuator realizes this action. Juggling, for instance, relies on feedback loops from the eye to the hands through the brain. Transferring the feedback concept to the quantum world faces a fundamental difficulty: quantum measurement changes randomly the state of the system and this change must be taken into account in the feedback procedure. In our first demonstration experiment, we have chosen as an operating point a fixed photon number in our cavity. The “eye” in this “photon juggling game” is the beam of Rydberg atoms which performs a weak QND measurement extracting a partial information about the photon number. The “brain” is a computer using this information to estimate in real time the state of the field in the cavity and the “hand” is a classical microwave source feeding the cavity. These operations are performed in successive loops bringing the field towards the desired photon number. Subsequent quantum jumps of the field are detected by the computer and their effect is reversed by the feedback procedure. In this way, a pre-determined photon number is maintained in a steady state. We hope to be able to extend soon these experiments to the protection of other non-classical states such as Schrödinger cats of radiation.

  • Dr. Peter Rosenbusch

  • Invited speaker: Dr. Peter Rosenbusch
    Affiliation: Observatoire de Paris
    Title: Atomic Clocks, Exchange Interaction And Giant Coherence Times
    Time and room: 17:15, lecture hall IAP
    Abstract: Thanks to atomic clocks the second is the best realised SI unit with a relative accuracy of today 2x 10^-16. In addition to time keeping, these laboratory devices perform powerful tests of fundamental physics such as tests of general relativity or the constancy of constants. The SYRTE is the French national laboratory of standards regarding time and frequency. It operates about 15 clocks and interferometers using laser cooled atoms of various kinds. We will present an overview of the SYRTE’s activities including strategies to improve the clock and interferometer sensitivity. We will focus on a Trapped Atom Clock on a Chip, where magnetic confinement is used to increase the experiment time and hence reduce the spectroscopic linewidth. The trap increases the atom density by 4 orders of magnitude such that novel phenomena arise from the atom-atom interactions: for an ensemble of thermal atoms, we observe giant coherence times of 58+/-12 s. The underlying new mechanism based on the exchange interaction is of such a general nature that it is applicable in many cold atom experiments and possibly other systems.

  • Serge Rosenblum

  • Invited speaker: Serge Rosenblum
    Affiliation: Faculty of Chemistry, Weizmann Institute of Science, Rehovot, Israel
    Time and room: 9:00 h, IAP Conference Room

  • Prof. Axel Kuhn

  • Invited speaker: Prof. Axel Kuhn
    Affiliation: University of Oxford
    Title: Single-Photon Shaping and Storage in Cavity-QED (or the "Tower-Bridge Photon")
    Time and room: 17:15, seminar room 1 in HISKP
    Abstract: We investigate the feasibility of implementing elementary light-matter interfaces for quantum networking. The combination of a deterministic single photon source based on vacuum stimulated adiabatic rapid passage [1,2], and a quantum memory is outlined [3,4]. Both systems are able to produce and process temporally shaped photonic wavepackets, and also provide a way of maintaining the indistinguishability of retrieved and original photons.

    Single atoms coupled to high-finesse cavities provide a unique way to deterministically generate a stream of single photons of small bandwidth [1]. We report on our latest results obtained with a strongly coupled atom-cavity system based on 87Rb. Atoms are injected into the cavity (Finesse F=80,000, L=80 μm) with an atomic fountain, which gives rise to atom-cavity interaction times of up to 0.5 ms. We demonstrate that this arrangement is a highly efficient source delivering indistinguishable single photons of arbitrary temporal shape [5], and we show how to derive analytic expressions for the optimum driving laser pulse [2]. Furthermore, we show that one can successfully imprint arbitrary phase jumps to individual photons and monitor these with a two-photon interference experiment of the Hong-Ou-Mandel type. Based on the successful photon generation, it is discussed how to invert the process such that a single atom absorbs a single impinging photon of arbitrary given shape with a probability close to unity. To do so, we analytically derive the shape of the driving pulse required to maintain impedance matching of the cavity to the incoming photonic wavepacket throughout its whole duration [4].

    We also report on the control of trapped atoms with optical tweezers [6]. This new technique allows handling many atoms independently, and therefore paves the way to QIP with scalable atomic arrays.

    [1] A. Kuhn and D. Ljunggren, “Cavity-based single-photon sources,” Contemporary Physics 51, 289 (2010); [2] G.S. Vasilev, D. Ljunggren, and A. Kuhn, “Single-photons made-to-measure,” New Journal of Physics 12, 063024 (2010); [3] M. Himsworth, P.B.R. Nisbet, J. Dilley, G. Langfahl-Klabes, and A. Kuhn, “EIT-based quantum memory for single photons from cavity-QED,” Appl. Phys. B 103, 579-589 (2011); [4] J. Dilley, P.B.R. Nisbet, B.W. Shore, and A. Kuhn, “Cavity-based single-atom quantum memory,” submitted, arXiv:1105:1699 [quant-ph]; [5] P. Nisbet, J. Dilley, and A. Kuhn, “Highly efficient source for indistinguishable photons of controlled shape,” submitted, arXiv:1106.6292v1 [quant-ph]; [6] L. Brandt, C. Muldoon, T. Thiele, J. Dong, E. Brainis, and A. Kuhn, “Spatial light modulators for the manipulation of individual atoms,” Appl. Phys. B 102, 443-450 (2011)