# Quantum technologies

Dieter Meschede's research group
Publications - Trapped Atoms as Qubits

### 2006

• Y. Miroshnychenko, W. Alt, I. Dotsenko, L. Förster, M. Khudaverdyan, D. Meschede, D. Schrader and A. Rauschenbeutel
An atom-sorting machine, Nature 442, 151 (2006)BibTeX
ABSTRACT »
Laser cooling and trapping techniques allow us to control and manipulate neutral atoms. Here we rearrange, with submicrometre precision, the positions and ordering of laser-trapped atoms within strings by manipulating individual atoms with optical tweezers. Strings of equidistant atoms created in this way could serve as a scalable memory for quantum information.
• D. Meschede and A. Rauschenbeutel
Manipulating single atoms, Adv. At. Mol. Opt. Phys. 53, 75 (2006)BibTeX
ABSTRACT »
Neutral atoms are interesting candidates for experimentally investigating the transition from well-understood quantum objects to many particle and macroscopic physics. Furthermore, the ability to control neutral atoms at the single atom level opens new routes to applications such as quantum information processing and metrology. We summarize experimental methods and findings in the preparation, detection, and manipulation of trapped individual neutral atoms. The high efficiency and the observed long coherence times of the presented methods are favorable for future applications in quantum information processing.
• Y. Miroshnychenko, W. Alt, I. Dotsenko, L. Förster, M. Khudaverdyan, A. Rauschenbeutel and D. Meschede
Precision preparation of strings of trapped neutral atoms, New J. Phys. 8, 191 (2006)arXivBibTeX
ABSTRACT »
We have recently demonstrated the creation of regular strings of neutral caesium atoms in a standing wave optical dipole trap using optical tweezers [Y. Miroshnychenko et al., Nature, in press (2006)]. The rearrangement is realized atom-by-atom, extracting an atom and re-inserting it at the desired position with sub-micrometer resolution. We describe our experimental setup and present detailed measurements as well as simple analytical models for the resolution of the extraction process, for the precision of the insertion, and for heating processes. We compare two different methods of insertion, one of which permits the placement of two atoms into one optical micropotential. The theoretical models largely explain our experimental results and allow us to identify the main limiting factors for the precision and efficiency of the manipulations. Strategies for future improvements are discussed.
• L. Förster, W. Alt, I. Dotsenko, M. Khudaverdyan, D. Meschede, Y. Miroshnychenko, S. Reick and A. Rauschenbeutel
BibTeX
ABSTRACT »
We implement a technique for loading a preset number of up to 19 atoms from a magneto-optical trap into a standing wave optical dipole trap. The efficiency of our technique is characterized by measuring the atom number before and after the loading process. Our analysis reveals details of the trap dynamics that are usually masked when working with larger atomic ensembles. In particular, we identify a low-loss collisional blockade mechanism. It forces the atoms to redistribute in the periodic potential until they are all stored in individual trapping sites, thereby strongly reducing site occupation number fluctuations.
• Y. Miroshnychenko, W. Alt, I. Dotsenko, L. Förster, M. Khudaverdyan, D. Meschede, S. Reick and A. Rauschenbeutel
Inserting two atoms into a single optical micropotential, Phys. Rev. Lett. 97, 243003 (2006)arXivBibTeX
ABSTRACT »
We recently demonstrated that strings of trapped atoms inside a standing wave optical dipole trap can be rearranged using optical tweezers [Y. Miroshnychenko et al., Nature, in press (2006)]. This technique allows us to actively set the interatomic separations on the scale of the individual trapping potential wells. Here, we use such a distance-control operation to insert two atoms into the same potential well. The detected success rate of this manipulation is 16(+4/-3) %, in agreement with the predictions of a theoretical model based on our independently determined experimental parameters.

### 2005

• M. Khudaverdyan, W. Alt, I. Dotsenko, L. Förster, S. Kuhr, D. Meschede, Y. Miroshnychenko, D. Schrader and A. Rauschenbeutel
Adiabatic Quantum State Manipulation of Single Trapped Atoms, Phys. Rev. A 71, 031404 (2005)arXivBibTeX
ABSTRACT »
We use microwave induced adiabatic passages for selective spin flips within a string of optically trapped individual neutral Cs atoms. We position-dependently shift the atomic transition frequency with a magnetic field gradient. To flip the spin of a selected atom, we optically measure its position and sweep the microwave frequency across its respective resonance frequency. We analyze the addressing resolution and the experimental robustness of this scheme. Furthermore, we show that adiabatic spin flips can also be induced with a fixed microwave frequency by deterministically transporting the atoms across the position of resonance.
• S. Kuhr, W. Alt, D. Schrader, I. Dotsenko, Y. Miroshnychenko, A. Rauschenbeutel and D. Meschede
Analysis of dephasing mechanisms in a standing-wave dipole trap, Phys. Rev. A 72, 023406 (2005)arXivBibTeX
ABSTRACT »
We study in detail the mechanisms causing dephasing of hyperfine coherences of cesium atoms confined by a far off-resonant standing wave optical dipole trap [S. Kuhr et al., Phys. Rev. Lett. 91, 213002 (2003)]. Using Ramsey spectroscopy and spin echo techniques, we measure the reversible and irreversible dephasing times of the ground state coherences. We present an analytical model to interpret the experimental data and identify the homogeneous and inhomogeneous dephasing mechanisms. Our scheme to prepare and detect the atomic hyperfine state is applied at the level of a single atom as well as for ensembles of up to 50 atoms.

### 2004

• D. Schrader, I. Dotsenko, M. Khudaverdyan, Y. Miroshnychenko, A. Rauschenbeutel and D. Meschede
Neutral Atom Quantum Register, Phys. Rev. Lett. 93, 150501 (2004)arXivBibTeX
ABSTRACT »
We demonstrate the realization of a quantum register using a string of single neutral atoms which are trapped in an optical dipole trap. The atoms are selectively and coherently manipulated in a magnetic field gradient using microwave radiation. Our addressing scheme operates with a high spatial resolution and qubit rotations on individual atoms are performed with 99% contrast. In a final read-out operation we analyze each individual atomic state. Finally, we have measured the coherence time and identified the predominant dephasing mechanism for our register.
• 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.

### 2003

• Y. Miroshnychenko, D. Schrader, S. Kuhr, W. Alt, I. Dotsenko, M. Khudaverdyan, A. Rauschenbeutel and D. Meschede
Continued imaging of the transport of a single neutral atom, Opt. Express 11, 3498-3502 (2003)BibTeX
ABSTRACT »
We have continuously imaged the controlled motion of a single atom as well as of a small number of distinguishable atoms with observation times exceeding one minute. The Cesium atoms are confined to potential wells of a standing wave optical dipole trap which allows to transport them over macroscopic distances. The atoms are imaged by an intensified CCD camera, and spatial resolution near the diffraction limit is obtained.
• 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.

### 2002

• W. Alt
An objective lens for efficient fluoresence detection of single atoms, Optik 113, 142 (2002)arXivBibTeX
ABSTRACT »
We present the design of a diffraction limited, long working distance monochromatic objective lens for efficient light collection. Consisting of four spherical lenses, it has a numerical aperture of 0.29, an effective focal length of 36 mm and a working distance of 36.5 mm. This inexpensive system allows us to detect 8·10^4 fluorescence photons per second from a single cesium atom stored in a magneto-optical trap.

### 2001

• 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.

### 2000

• 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.