G. Hétet

Karlsruhe Institute of Technology, Karlsruhe, Baden-Wuerttemberg, Germany

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Publications (36)136.48 Total impact

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    ABSTRACT: We perform a free-space measurement and control of the refractive index of a single trapped ion in the presence of quantum interference effects. The single atom refractive index is characterized by the Faraday rotation of a laser field tightly focused onto a trapped and laser-cooled barium ion. It is tuned using the internal ion state that is optically controlled via a V or a Λ scheme. Measurements of the phase shift associated with an electromagnetically induced transparency are then performed and the internal state on the qubit transition is read-out with a detection fidelity of (98±1)%.
    Physical Review A 10/2013; 88(4). · 3.04 Impact Factor
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    ABSTRACT: We perform a high-resolution real-time readout of the motion of a single trapped and laser-cooled Ba^{+} ion. By using an interferometric setup, we demonstrate a shot-noise-limited measurement of thermal oscillations with a resolution of 4 times the standard quantum limit. We apply the real-time monitoring for phase control of the ion motion through a feedback loop, suppressing the photon recoil-induced phase diffusion. Because of the spectral narrowing in the phase-locked mode, the coherent ion oscillation is measured with a resolution of about 0.3 times the standard quantum limit.
    Physical Review Letters 03/2013; 110(13):133602. · 7.73 Impact Factor
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    ABSTRACT: A scheme for entangling distant atoms is realized, as proposed in the seminal paper by [C. Cabrillo et al., Phys. Rev. A 59, 1025 (1999)]. The protocol is based on quantum interference and detection of a single photon scattered from two effectively one meter distant laser cooled and trapped atomic ions. The detection of a single photon heralds entanglement of two internal states of the trapped ions with high rate and with a fidelity limited mostly by atomic motion. Control of the entangled state phase is demonstrated by changing the path length of the single-photon interferometer.
    Physical Review Letters 02/2013; 110(8):083603. · 7.73 Impact Factor
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    ABSTRACT: Faraday rotation of a laser field induced by a single atom is demonstrated by tightly focussing a linearly polarized laser beam onto a laser-cooled ion held in a harmonic Paul trap. The polarization rotation signal is further used to measure the phase-shift associated with electromagnetically-induced-transparency and to demonstrate read-out of the internal state on the qubit transition with a detection fidelity of 98 $\pm$ 1%. These results have direct implications for single atom magnetometery and dispersive read-out of atomic superpositions.
    12/2012;
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    ABSTRACT: We investigate the quantum electrodynamic (QED) properties of an atomic electron close to the focus of a spherical mirror. We first show that the spontaneous emission and excited-state level shift of the atom can be fully suppressed with mirror-atom distances of many wavelengths. A three-dimensional theory predicts that the spectral density of vacuum fluctuations can indeed vanish within a volume λ3 around the atom, with the use of a far-distant mirror covering only half of the atomic emission solid angle. The modification of these QED atomic properties is also computed as a function of the mirror size, and large effects are found for only moderate numerical apertures. We also evaluate the long-distance ground-state energy shift (Casimir-Polder shift) and find that it scales as (λ/R)2 at the focus of a hemispherical mirror of radius R, as opposed to the well-known (λ/R)4 scaling law for an atom at a distance R from an infinite plane mirror. Our results are relevant for investigations of QED effects as well as free-space coupling to single atoms using high-numerical-aperture lenses.
    Physical Review A 11/2012; 82:063812. · 3.04 Impact Factor
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    ABSTRACT: We propose a quantum memory protocol where a input light field can be stored onto and released from a single ground state atomic ensemble by controlling dynamically the strength of an external static and homogeneous field. The technique relies on the adiabatic following of a polaritonic excitation onto a state for which the forward collective radiative emission is forbidden. The resemblance with the archetypal Electromagnetically-Induced-Transparency (EIT) is only formal because no ground state coherence based slow-light propagation is considered here. As compared to the other grand category of protocols derived from the photon-echo technique, our approach only involves a homogeneous static field. We discuss two physical situations where the effect can be observed, and show that in the limit where the excited state lifetime is longer than the storage time, the protocols are perfectly efficient and noise-free. We compare the technique to other quantum memories, and propose atomic systems where the experiment can be realized.
    New Journal of Physics 08/2012; 15(4). · 4.06 Impact Factor
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    ABSTRACT: State mapping between atoms and photons and photon-photon interactions play an key role in scalable quantum information processing. First, we consider the interaction of a single atom with a quantized light pulse propagating in free space. We show the dependence of the atomic excitation on (i) the quantum state of the pulse and (ii) the overlap between the pulse waveform and the atomic dipole pattern. We present a detailed study for both n-photon Fock state and coherent state pulses with various temporal shapes. The work is extended to the dynamics of two spatial modes propagating from opposite directions to the atom. Second, we propose a setup for quantum memory based on a single two-level atom in a half cavity with a moving mirror. We show that various temporal shapes of incident photon can be efficiently stored and readout by shaping the time-dependent decay rate γ(t) describing the interaction between the atom and the light. We present an analytical expression for the efficiency of the storage and study its dependence on the ratio between the incident light field bandwidth and the atomic decay rate. We discuss possible implementations and experimental issues, particularly for a single atom or ion in a half cavity as well as a superconducting qubit in the circuit QED.
    06/2012;
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    ABSTRACT: Efficient self-interference of single photons emitted by a sideband-cooled barium ion is demonstrated. First, the technical tools for performing efficient coupling to the quadrupolar transition of a single 138Ba+ ion are presented. We show efficient Rabi oscillations of the internal state of the ion by using a highly stabilized 1.76-μm fiber laser resonant with the S1/2-D5/2 transition. We then show sideband cooling of the ion's motional modes and use it as a means to enhance the interference contrast of the ion with its mirror image to up to 90%. Last, we measure the dependence of the self-interference contrast on the mean phonon number, thereby demonstrating the potential of the setup for single-atom thermometry close to the motional ground state.
    Physical Review A 01/2012; · 3.04 Impact Factor
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    ABSTRACT: We propose a setup for quantum memory based on a single two-level atom in a half cavity with a moving mirror. We show that various temporal shapes of incident photon can be efficiently stored and readout by shaping the time-dependent decay rate $\gamma(t)$ between the atom and the light. This is achieved uniquely by an appropriate motion of the mirror without the need for additional control laser or atomic level. We present an analytical expression for the efficiency of the process and study its dependence on the ratio between the incident light field bandwidth and the atomic decay rate. We discuss possible implementations and experimental issues, particularly for a single atom or ion in a half cavity quantum optical setup as well as a superconducting qubit in the context of circuit QED.
    Physical Review A 11/2011; 85(1). · 3.04 Impact Factor
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    ABSTRACT: We present experimental results demonstrating 87% efficiency for single pulse recall, and storage of up to 20 pulses using a three level gradient echo memory with hot rubidium vapour as the storage medium. We also present results showing pulse resequencing, as well as pulse splitting and spectral manipulation. The decoherence mechanisms affecting the system, in particular scattering due to the control field and how it can be minimised by turning the control field off during storage, are also discussed.
    AIP Conference Proceedings. 10/2011; 1363(1):383-388.
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    ABSTRACT: We report absorption experiments from a single trapped atom. We focus a weak and narrow band Gaussian light beam onto an optically cooled 138Ba+ ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.35%. Using this result, we then demonstrate Electromagnetically-Induced-Transparency (EIT) of the ion and present a novel set-up where the single ion is used as a mirror in a Fabry-Perrot type cavity.
    10/2011;
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    ABSTRACT: By tightly focusing a laser field onto a single cold ion trapped in front of a far-distant dielectric mirror, we could observe a quantum electrodynamic effect whereby the ion behaves as the optical mirror of a Fabry-Pérot cavity. We show that the amplitude of the laser field is significantly altered due to a modification of the electromagnetic mode structure around the atom in a novel regime in which the laser intensity is already changed by the atom alone. We propose a direct application of this system as a quantum memory for single photons.
    Physical Review Letters 09/2011; 107(13):133002. · 7.73 Impact Factor
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    ABSTRACT: Export Date: 30 July 2012, Source: Scopus, doi: 10.1063/1.3630216, Language of Original Document: English, Correspondence Address: Buchler, B.C.; ARC Centre of Excellence for Quantum-Atom Optics, Department of Quantum Science, Australian National University, Canberra, ACT 0200, Australia, References: Julsgaard, B., Sherson, J., Cirac, J.I., Flurášek, J., Polzik, E.S., (2004) Nature, 432, p. 482;, Sponsors: Aust. Res. Counc. Cent. Excellence Quantum Comput. Technol.; Tamagawa University; Aust. Res. Counc. Cent. Excellence Quantum-Atom Opt.; Res. Lab. Electron. Massachusetts Inst. Technol.; NewSpec Pty Ltd
    AIP Conference Proceedings; 01/2011
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    ABSTRACT: Conference code: 89833, Export Date: 30 July 2012, Source: Scopus, Art. No.: 6193812, doi: 10.1109/IQEC-CLEO.2011.6193812, Language of Original Document: English, Correspondence Address: Sparkes, B.M.; Department of Quantum Science, Research School of Physics and Engineering, Australian National University, Canberra, ACT, Australia; email: ben.sparkes@anu.edu.au, References: Hosseini, M., Sparkes, B.M., Campbell, G., Lam, P.K., Buchler, B.C., High efficiency coherent optical memory with warm rubidium vapour (2010) Nature Commun., 2, p. 174;, Sponsors: Australian National University (ANU); Macquarie University, MQ Photonics Research Centre; The University of Sydney, School of Physics; The University of Queensland (UQ); Griffith University
    2011 Int. Quantum Electron. Conf., IQEC 2011 and Conf. Lasers and Electro-Optics, CLEO Pacific Rim 2011 Incorporating the Australasian Conf. Optics, Lasers and Spectroscopy and the Australian Conf.; 01/2011
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    ABSTRACT: In this Letter, we report an absorption spectroscopy experiment and the observation of electromagnetically induced transparency from a single trapped atom. We focus a weak and narrow band Gaussian light beam onto an optically cooled 138Ba+ ion using a high numerical aperture lens. Extinction of this beam is observed with measured values of up to 1.35%. We demonstrate electromagnetically induced transparency of the ion by tuning a strong control beam over a two-photon resonance in a three-level Λ-type system. The probe beam extinction is inhibited by more than 75% due to population trapping.
    Physical Review Letters 10/2010; 105(15):153604. · 7.73 Impact Factor
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    ABSTRACT: The burgeoning fields of quantum computing and quantum key distribution have created a demand for a quantum memory. The gradient echo memory scheme is a quantum memory candidate for light storage that can boast efficiencies approaching unity, as well as the flexibility to work with either two or three level atoms. The key to this scheme is the frequency gradient that is placed across the memory. Currently the three level implementation uses a Zeeman gradient and warm atoms. In this paper we model a new gradient creation mechanism - the ac Stark effect - to provide an improvement in the flexibility of gradient creation and field switching times. We propose this scheme in concert with a move to cold atoms (~1 mK). These temperatures would increase the storage times possible, and the small ensemble volumes would enable large ac Stark shifts with reasonable laser power. We find that memory bandwidths on the order of MHz can be produced with experimentally achievable laser powers and trapping volumes, with high precision in gradient creation and switching times on the order of nanoseconds possible. By looking at the different decoherence mechanisms present in this system we determine that coherence times on the order of 10s of milliseconds are possible, as are delay-bandwidth products of approximately 50 and efficiencies over 90%.
    Physical Review A 08/2010; · 3.04 Impact Factor
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    ABSTRACT: Photon echo schemes are excellent candidates for high efficiency coherent optical memory. They are capable of high-bandwidth multipulse storage, pulse resequencing and have been shown theoretically to be compatible with quantum information applications. One particular photon echo scheme is the gradient echo memory (GEM). In this system, an atomic frequency gradient is induced in the direction of light propagation leading to a Fourier decomposition of the optical spectrum along the length of the storage medium. This Fourier encoding allows precision spectral manipulation of the stored light. In this Letter, we show frequency shifting, spectral compression, spectral splitting, and fine dispersion control of optical pulses using GEM.
    Optics Letters 04/2010; 35(7):1091-3. · 3.39 Impact Factor
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    ABSTRACT: The bandwidth and versatility of optical devices have revolutionized information technology systems and communication networks. Precise and arbitrary control of an optical field that preserves optical coherence is an important requisite for many proposed photonic technologies. For quantum information applications, a device that allows storage and on-demand retrieval of arbitrary quantum states of light would form an ideal quantum optical memory. Recently, significant progress has been made in implementing atomic quantum memories using electromagnetically induced transparency, photon echo spectroscopy, off-resonance Raman spectroscopy and other atom-light interaction processes. Single-photon and bright-optical-field storage with quantum states have both been successfully demonstrated. Here we present a coherent optical memory based on photon echoes induced through controlled reversible inhomogeneous broadening. Our scheme allows storage of multiple pulses of light within a chosen frequency bandwidth, and stored pulses can be recalled in arbitrary order with any chosen delay between each recalled pulse. Furthermore, pulses can be time-compressed, time-stretched or split into multiple smaller pulses and recalled in several pieces at chosen times. Although our experimental results are so far limited to classical light pulses, our technique should enable the construction of an optical random-access memory for time-bin quantum information, and have potential applications in quantum information processing.
    Nature 09/2009; 461(7261):241-5. · 38.60 Impact Factor
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    ABSTRACT: We investigate the properties of a recently proposed gradient echo memory (GEM) scheme for information mapping between optical and atomic systems. We show that GEM can be described by the dynamic formation of polaritons in k space. This picture highlights the flexibility and robustness with regards to the external control of the storage process. Our results also show that, as GEM is a frequency-encoding memory, it can accurately preserve the shape of signals that have large time-bandwidth products, even at moderate optical depths. At higher optical depths, we show that GEM is a high fidelity multimode quantum memory.
    Physical Review Letters 12/2008; 101(20):203601. · 7.73 Impact Factor
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    ABSTRACT: We propose a photon echo quantum memory scheme using detuned Raman coupling to long-lived ground states. In contrast to previous three-level schemes based on controlled reversible inhomogeneous broadening that use sequences of pi pulses, the scheme does not require accurate control of the coupling dynamics to the ground states. We present a proof-of-principle experimental realization of our proposal using rubidium atoms in a warm vapor cell. The Raman resonance line is broadened using a magnetic field that varies linearly along the direction of light propagation. Inverting the magnetic field gradient rephases the atomic dipoles and re-emits the light pulse in the forward direction.
    Optics Letters 11/2008; 33(20):2323-5. · 3.39 Impact Factor

Publication Stats

424 Citations
136.48 Total Impact Points

Institutions

  • 2013
    • Karlsruhe Institute of Technology
      • Physikalisches Institut
      Karlsruhe, Baden-Wuerttemberg, Germany
  • 2010–2013
    • University of Innsbruck
      • Institut für Experimentalphysik
      Innsbruck, Tyrol, Austria
  • 2008–2011
    • University of Otago
      • Department of Physics
      Dunedin, Otago, New Zealand
  • 2006–2011
    • Australian National University
      • Department of Quantum Science (DQS)
      Canberra, Australian Capital Territory, Australia