# Quantum technologies

Dieter Meschede's research group
Group members
Victor Gomer
 Last positionin our group: Postdoc
 Field of researchin our group: Cavity QED

## Publications(up to 2004)

• I. Dotsenko, W. Alt, S. Kuhr, D. Schrader, M. Müller, Y. Miroshnychenko, V. Gomer, A. Rauschenbeutel and D. Meschede
Application of electro-optically generated light fields for Raman spectroscopy of trapped Cesium atoms, Appl. Phys. B 78, 711-717 (2004)BibTeX
ABSTRACT »
We present an apparatus for generating a multi-frequency laser field to coherently couple the F=3 and F=4 ground state of trapped cesium atoms through Raman transitions. We use a single frequency diode laser and generate sidebands by means of a 9.2 GHz electro-optic modulator. With an interferometer, we separated the sidebands and carrier, sending them to the trapped atoms in opposite directions. The Rabi oscillation of the populations of F=3 and F=4 is monitored. We find that due to destructive quantum interference of two simultaneous Raman transitions the expected Rabi frequency is reduced by a factor that is in quantitative agreement with theoretical expectations. It is demonstrated how this interference can be suppressed experimentally. Besides, we demonstrate the application of the setup for Raman spectroscopy of Zeeman sublevels and of the vibrational states of a small number of trapped atoms.
• D. Schrader, S. Kuhr, W. Alt, Y. Miroshnychenko, I. Dotsenko, W. Rosenfeld, M. Khudaverdyan, V. Gomer, A. Rauschenbeutel and D. Meschede
Controlled transport of single neutral atom qubits, Proceedings of the 16th ICOLS, (2003)BibTeX
ABSTRACT »
We have prepared and detected quantum coherences of trapped cesium atoms with long dephasing times. Controlled transport by an “optical conveyor belt” over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. The dominating dephasing effects are experimentally identified and found to be of technical rather than fundamental nature.
• S. Kuhr, W. Alt, D. Schrader, I. Dotsenko, Y. Miroshnychenko, W. Rosenfeld, M. Khudaverdyan, V. Gomer, A. Rauschenbeutel and D. Meschede
Coherence properties and quantum state transportation in an optical conveyor belt, Phys. Rev. Lett. 91, 213002 (2003)arXivBibTeX
ABSTRACT »
We have prepared and detected quantum coherences with long dephasing times at the level of single trapped cesium atoms. Controlled transport by an "optical conveyor belt" over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. The limiting dephasing effects are experimentally identified and are of technical rather than fundamental nature. We present an analytical model of the reversible and irreversible dephasing mechanisms. Coherent quantum bit operations along with quantum state transport open the route towards a "quantum shift register" of individual neutral atoms.
• W. Alt, D. Schrader, S. Kuhr, M. Müller, V. Gomer and D. Meschede
Single atoms in a standing-wave dipole trap, Phys. Rev. A 67, 033403 (2003)arXivBibTeX
ABSTRACT »
We trap a single cesium atom in a standing-wave optical dipole trap. Special experimental procedures, designed to work with single atoms, are used to measure the oscillation frequency and the atomic energy distribution in the dipole trap. These methods rely on unambiguously detecting presence or loss of the atom using its resonance fluorescence in the magneto-optical trap.
• B. Ueberholz, S. Kuhr, D. Frese, V. Gomer and D. Meschede
Cold collisions in a high-gradient magneto-optical trap, J. Phys. B: At. Mol. Opt. Phys. 35, 4899 (2002)BibTeX
ABSTRACT »
We present a detailed analysis of the cold collision measurements performed in a high-gradient magneto-optical trapwith a few trapped Cs atomsfirst presented in Ueberholz et al (J. Phys. B: At.Mol. Opt. Phys. 33 (2000) L135). The ability to observe individual loss events allows us to identify two-body collisions that lead to the escape of only one of the colliding atoms (up to 10% of all collisional losses). Possible origins of these events are discussed here. We also observed strong modifications of the total loss rate with variations in the repumping laser intensity. This is explained by a simple semiclassical model based on optical suppression of hyperfine-changing collisions between ground-state atoms.
• S. Kuhr, W. Alt, D. Schrader, M. Müller, V. Gomer and D. Meschede
Deterministic Delivery of a Single Atom, Science 293, 278 (2001)BibTeX
ABSTRACT »
We report the realization of a deterministic source of single atoms. A standing-wave dipole trap is loaded with one or any desired number of cold cesium atoms from a magneto-optical trap. By controlling the motion of the standing wave, we adiabatically transport the atom with submicrometer precision over macroscopic distances on the order of a centimeter. The displaced atom is observed directly in the dipole trap by fluorescence detection. The trapping field can also be accelerated to eject a single atom into free flight with well-defined velocities.
• D. Schrader, S. Kuhr, W. Alt, M. Müller, V. Gomer and D. Meschede
An optical conveyor belt for single neutral atoms, Appl. Phys. B 73, 819 (2001)arXivBibTeX
ABSTRACT »
Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical "single-atom conveyor belt" represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand.
• V. Gomer and D. Meschede
A single trapped atom: Light-matter interaction at the microscopic level, Ann. Phys. (Leipzig) 10, 9-18 (2001)BibTeX
ABSTRACT »
For a single trapped atom the fluctuations of resonance fluorescence reveal its dynamic evolution at all relevant time scales. We review experimental results, extend interpretations and express expectations for future systems with fully controlled quantum properties.
• D. Frese, B. Ueberholz, S. Kuhr, W. Alt, D. Schrader, V. Gomer and D. Meschede
Single Atoms in an Optical Dipole Trap: Towards a Deterministic Source of Cold Atoms, Phys. Rev. Lett. 85, 3777 (2000)arXivBibTeX
ABSTRACT »
We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of 100% and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of $4.2\pm 0.7$ s has been measured. Possible applications are briefly discussed.
• H. Schadwinkel, V. Gomer, U. Reiter, B. Ueberholz and D. Meschede
Quantum Fluctuations of a Single Trapped Atom: Transient Rabi Oscillations and Magnetic Bistability, IEEE J. of Quantum Electronics 36, 1358 (2000)arXivBibTeX
ABSTRACT »
Isolation of a single atomic particle and monitoring its resonance fluorescence is a powerful tool for studies of quantum effects in radiation-matter interactions. We present observations of quantum dynamics of an isolated neutral atom stored in a magneto-optical trap. By means of photon orrelations in the atom's resonance fluorescence we demonstrate the well-known phenomenon of photon antibunching which corresponds to transient Rabi oscillations in the atom. Through polarization-sensitive photon correlations, we show a novel example of resolved quantum fluctuations: pontaneous magnetic orientation of an atom. These effects can only be observed with a single atom.
• B. Ueberholz, S. Kuhr, D. Frese, D. Meschede and V. Gomer
Counting Cold Collisions, J. Phys. B: At. Mol. Opt. Phys. 33, L135 (2000)arXivBibTeX
ABSTRACT »
We have experimentally explored a novel possibility to study exoergic cold atomic collisions. Trapping of small countable atom numbers in a shallow magneto-optical trap and monitoring of their temporal dynamics allows us to directly observe isolated two-body atomic collisions and provides detailed information on loss statistics. A substantial fraction of such cold collisional events has been found to result in the loss of one atom only. We have also observed for the first time a strong optical suppression of ground-state hyperfine-changing collisions in the trap by its repump laser field.
• H. Schadwinkel, U. Reiter, V. Gomer and D. Meschede
Magneto-optical trap as an optical lattice, Phys. Rev. A 61, 013409 (1999)BibTeX
ABSTRACT »
We study the magneto-optical trap (MOT) as an optical lattice with a setup providing full phase control for all light fields. Although completely different light fields are possible for various phases, we have found experimental evidence that stored atoms are generally localized in micropotentials of the six-beam lattice. The influence of the phase variation is surprisingly small, suggesting that the robust behavior of the MOT is a consequence of this fact. We find furthermore good agreement of our experimental data with a simple theoretical model which reduces the complicated MOT to a description of steady-state atoms localized at points of the deepest adiabatic light-shift potential.
• V. Gomer, F. Strauch, B. Ueberholz, S. Knappe and D. Meschede
Single-atom dynamics revealed by photon correlations, Phys. Rev. A 58, R1657 (1998)BibTeX
ABSTRACT »
We have studied a single neutral atom stored in a magneto-optical trap by recording arrival times of fluorescence photons emitted by the atom. Photon correlations at nanosecond scales (Rabi oscillations), at microseconds (intensity and polarization correlations), and also at milliseconds (position correlations) reveal the dynamical behavior of the atomic excitation, of the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size.
• D. Meschede, V. Gomer and H. Monien
Atomic Bose-Einstein Condensates: A Model for Macroscopic Quantum Systems, Naturwissenschaften 85, 203 85, 203-218 (1998)BibTeX
ABSTRACT »
A novel type of macroscopic quantum system has recently become available through the experimental realization of Bose condensates from neutral atoms. We review experimental results and the elementary quantum mechanical approach and outline advanced theoretical concepts regarding finite size, potentials, dimensionality, and interactions.
• V. Gomer, B. Ueberholz, S. Knappe, F. Strauch, D. Frese and D. Meschede
Decoding the dynamics of a single trapped atom from photon correlations, Appl. Phys. B 67, 689 (1998)BibTeX
ABSTRACT »
Information on the dynamics of a single neutral atom can be decoded from fluctuations in the resonance fluorescence. We have measured two-time photon correlations of individual cesium atoms stored in a magneto-optical trap. We observe strong correlations at nanosecond scales (Rabi oscillations), at microseconds (intensity and polarization correlations), and also at milliscconds (position correlations) revealing the dynamical behavior of the atomic excitation, of the atomic orientation, and of its transport in the trap at both the optical wavelength scale and the trap size. In this article we compare our experimental results with a simplified model of an atom moving through an optical lattice. We investigate the influence of light-field topogaphy and of the multilevel character of the atom on the shape and the visibility of the correlations.
• A. Rauschenbeutel, H. Schadwinkel, V. Gomer and D. Meschede
Standing light fields for cold atoms with intrinsically stable and variable time phases, Opt. Comm. 148, 45 (1998)BibTeX
ABSTRACT »
We present a novel method to realise a standing light field with a stable configuration in two or three dimensions. A single standing wave formed by two counterpropagating beams is folded and brought into intersection with itself. The values of the relative timephases are stable, a priori known, and can be altered arbitrarily by means of retardation plates. The polarisation configurations of three orthogonal standing waves include the standard magnetooptical trap and a novel three-dimensional pure polarisation lattice which we have investigated in a first spectroscopic measurement, providing strong evidence for atomic localisation in both cases.
• O. Harms, M. Zehnpfennig, V. Gomer and D. Meschede
Photodetachment spectroscopy of stored H- ions, J. Phys. B:. At. Mol. Phys. 30, 3781 (1997)BibTeX
ABSTRACT »

Threshold photodetachment of negative hydrogen ions stored in a Penning trap has been studied. The electron afﬁnity of hydrogen is determined to 6082.8(7) cm−1 in good agreement with previous experiments. The Wigner law has been found to be valid in a region of 400 cm−1 above the threshold.

• F. Strauch, V. Gomer, H. Schadwinkel, B. Ueberholz, D. Haubrich and D. Meschede
Diffraction by cold atoms, Opt. Comm. 145, 57 (1997)BibTeX
ABSTRACT »
We have observed diffraction of a laser probe beam by a trapped sample of cold atoms. The effect is only visible in the vicinity of a resonance line. The observed diffraction pattern arises from interference of the incident and scattered light wave, allowing reconstruction of geometric properties of the trapped sample from the holographic record.
• V. Gomer, O. Harms, D. Haubrich, H. Schadwinkel, F. Strauch, B. Ueberholz, S. aus der Wiesche and D. Meschede
Magnetostatic traps for charged and neutral particles, Hyperfine Interactions 109, 281-292 (1997)BibTeX
ABSTRACT »
We have constructed magnetostatic traps from permanent magnets for trapping charged and neutral atoms. Two storage experiments are presented: a compact Penning trap for light ions and magnetic trapping of single neutral atoms. The dynamics of cold neutral atoms and their loss mechanisms in a quadrupole magnetostatic trap are discussed.