Quantentechnologie
Dieter Meschede's research group
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Gruppenmitglieder Dieter Meschede
Gruppenmitglieder Dieter Meschede
Gruppenmitglieder
| Professor Dr. Dieter Meschede | |||||||||||||||||
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Publications
2012
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A digital atom interferometer with single particle control on a discretized spacetime geometry, Accepted, (2012)ABSTRACT »To appear.
2011
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Bound Molecules in an Interacting Quantum Walk, arXiv:1105.1051, (2011)arXiv
ABSTRACT »We investigate a system of two atoms in an optical lattice, performing a quantum walk by state-dependent shift operations and a coin operation acting on the internal states. The atoms interact, e.g., by cold collisions, whenever they are in the same potential well of the lattice. Under such conditions they typically develop a bound state, so that the two atoms effectively perform a quantum walk together, rarely moving further from each other than a few lattice sites. The theoretical analysis is based on a theory of quantum walks with a point defect, applied to the difference variable. We also discuss the feasibility of an experimental realization in existing quantum walk experiments.
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Direct Observation and Analysis of Spin-Dependent Transport of Single Atoms in a 1D Optical Lattice, J. Korean Phys. Soc. 59, 2947 (2011)arXivABSTRACT »We have directly observed spin-dependent transport of single cesium atoms in a 1D optical lattice. A superposition of two circularly polarized standing waves is generated from two counter propagating, linearly polarized laser beams. Rotation of one of the polarizations by $\pi$ causes displacement of the $\sigma^{+}$- and $\sigma^{-}$-lattices by one lattice site. Unidirectional transport over several lattice sites is achieved by rotating the polarization back and forth and flipping the spin after each transport step. We have analyzed the transport efficiency over 10 and more lattice sites, and discussed and quantified relevant error sources.
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Coherently Walking, Rocking and Blinding Single Neutral Atoms, J. Phys.: Conf. Ser. 264, 012021 (2011)ABSTRACT »Advances in the preparation and detection, but most importantly in the coherent manipulation of single neutral atoms have allowed the observation of intriguing phenomena of quantum physics in recent years. We discuss developments to prepare and detect single neutral atoms in a one-dimensional optical lattice potential with single site resolution. Moreover, using two different experimental techniques, a state-dependent optical lattice potential on the one hand and a high-finesse optical cavity on the other hand, we have obtained coherent control over single neutral atoms. The former has enabled us to observe the quantum walk of atoms in position space, and to coherently control the motion of trapped atoms via microwave radiation. The latter offers a means to non-destructively detect the atomic spin state, thereby revealing quantum jumps of single atoms, or the altered optical properties of single atoms when subject to electromagnetically-induced transparency.
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Optical nanofibers and spectroscopy, Applied Physics B 105, 3–15 (2011)arXivABSTRACT »We review our recent progress in the production and characterization of tapered optical fibers with a sub-wavelength diameter waist. Such fibers exhibit a pronounced evanescent field and are therefore a useful tool for highly sensitive evanescent wave spectroscopy of adsorbates on the fiber waist or of the medium surrounding. We use a carefully designed flame pulling process that allows us to realize preset fiber diameter profiles. In order to determine the waist diameter and to verify the fiber profile, we employ scanning electron microscope measurements and a novel accurate in situ optical method based on harmonic generation. We use our fibers for linear and non-linear absorption and fluorescence spectroscopy of surface-adsorbed organic molecules and investigate their agglomeration dynamics. Furthermore, we apply our spectroscopic method to quantum dots on the surface of the fiber waist and to caesium vapor surrounding the fiber. Finally, towards dispersive measurements, we present our first results on building and testing a single-fiber bi-modal interferometer.
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ABCD-treatment of a propagating doughnut beam generated by a spiral phase plate, Optics Express 19, 21205-21210 (2011)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.
2010
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Imprinting Patterns of Neutral Atoms in an Optical Lattice using Magnetic Resonance Techniques, New J. Phys. 12, 065027 (2010)arXivABSTRACT »We prepare arbitrary patterns of neutral atoms in a one-dimensional (1D) optical lattice with single-site precision using microwave radiation in a magnetic field gradient. We give a detailed account of the current limitations and propose methods to overcome them. Our results have direct relevance for addressing planes, strings or single atoms in higher-dimensional optical lattices for quantum information processing or quantum simulations with standard methods in current experiments. Furthermore, our findings pave the way for arbitrary single-qubit control with single-site resolution.
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Analyzing quantum jumps of one and two atoms strongly coupled to an optical cavity, J. Opt. Soc. Am. B 27, A152 (2010)arXivABSTRACT »We induce quantum jumps between the hyperfine ground states of one and two Cesium atoms, strongly coupled to the mode of a high-finesse optical resonator, and analyze the resulting random telegraph signals. We identify experimental parameters to deduce the atomic spin state nondestructively from the stream of photons transmitted through the cavity, achieving a compromise between a good signal-to-noise ratio and minimal measurement-induced perturbations. In order to extract optimum information about the spin dynamics from the photon count signal, a Bayesian update formalism is employed, which yields time-dependent probabilities for the atoms to be in either hyperfine state. We discuss the effect of super-Poissonian photon number distributions caused by atomic motion.
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Measurement of submicrometre diameters of tapered optical fibres using harmonic generation, Opt. Express 18, 7693–7704 (2010)ABSTRACT »Applications of subwavelength-diameter optical fibres in nonlinear optics require precise knowledge of the submicrometre fibre waist diameter. We demonstrate a new technique for optical measurement of the diameter based on second- and third-harmonic generation with an accuracy of better than 2%. To generate the harmonic light, inter-modal phase matching must be achieved. We find that the phase-matching condition allows us to unambiguously deduce the fibre diameter from the wavelength of the harmonic light. High-resolution scanning electron microscope imaging is used to verify the results.
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Optical control of the refractive index of a single atom, Phys. Rev. Lett. 105, 153603 (2010)arXivABSTRACT »We experimentally demonstrate the elementary case of electromagnetically induced transparency with a single atom inside an optical cavity probed by a weak field. We observe the modification of the dispersive and absorptive properties of the atom by changing the frequency of a control light field. Moreover, a strong cooling effect has been observed at two-photon resonance, increasing the storage time of our atoms twenty-fold to about 16 seconds. Our result points towards all-optical switching with single photons.
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Single Cs Atoms as Collisional Probes in a large Rb Magneto-Optical Trap, Phys. Rev. A 82, 042722 (2010)arXivABSTRACT »We study cold interspecies collisions of cesium and rubidium in a strongly imbalanced system with single and few Cs atoms. Observation of the single-atom fluorescence dynamics yields insight into light-induced loss mechanisms, while both subsystems can remain in steady state. This significantly simplifies the analysis of the dynamics, as Cs-Cs collisions are effectively absent and the majority component remains unaffected, allowing us to extract a precise value of the Rb-Cs collision parameter. Extending our results to ground-state collisions would allow to use single neutral atoms as coherent probes for larger quantum systems.
2009
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Nearest-Neighbor Detection of Atoms in a 1D Optical Lattice by Fluorescence Imaging, Phys. Rev. Lett. 102, 053001 (2009)arXivABSTRACT »We overcome the diffraction limit in fluorescence imaging of neutral atoms in a sparsely filled one-dimensional optical lattice. At a periodicity of 433 nm, we reliably infer the separation of two atoms down to nearest neighbors. We observe light induced losses of atoms occupying the same lattice site, while for atoms in adjacent lattice sites, no losses due to light induced interactions occur. Our method points towards characterization of correlated quantum states in optical lattice systems with filling factors of up to one atom per lattice site.
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Microwave Control of Atomic Motion in Optical Lattices, Phys. Rev. Lett. 103, 233001 (2009)arXivABSTRACT »We control the quantum mechanical motion of neutral atoms in an optical lattice by driving microwave transitions between spin states whose trapping potentials are spatially offset. Control of this offset with nanometer precision allows for adjustment of the coupling strength between different motional states, analogous to an adjustable effective Lamb-Dicke factor. This is used both for efficient one-dimensional sideband cooling of individual atoms to a vibrational ground state population of 97% and to drive coherent Rabi oscillation between arbitrary pairs of vibrational states. We further show that microwaves can drive well resolved transitions between motional states in maximally offset, shallow lattices, and thus in principle allow for coherent control of long-range quantum transport.
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Quantum Walk in Position Space with Single Optically Trapped Atoms, Science 325, 174 (2009)arXivABSTRACT »The quantum walk is the quantum analog of the well-known random walk, which forms the basis for models and applications in many realms of science. Its properties are markedly different from the classical counterpart and might lead to extensive applications in quantum information science. In our experiment, we implemented a quantum walk on the line with single neutral atoms by deterministically delocalizing them over the sites of a one-dimensional spin-dependent optical lattice. With the use of site-resolved fluorescence imaging, the final wave function is characterized by local quantum state tomography, and its spatial coherence is demonstrated. Our system allows the observation of the quantum-to-classical transition and paves the way for applications, such as quantum cellular automata.
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Strong effective saturation by optical pumping in three-level systems, Phys. Rev. A 80, 063801 (2009)ABSTRACT »We have studied nonlinear absorption from the In P1/2,3/2 ground-state doublet in a resistively heated high-temperature cell and a hollow cathode lamp. Using probe and pump lasers at 410 and 451 nm, respectively, absorption spectra with nonlinear properties caused by saturated absorption, coherent dark resonances, and optical pumping are observed. A theoretical description in terms of a density-matrix theory agrees very well with the observed spectra and identifies optical pumping as a dominating process of broadening in the stepwise contribution rather than velocity-changing collisions. Our experiments suggest that the theory used here is widely applicable in saturation spectroscopy on three-level Λ systems.
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Quantum jumps and spin dynamics of interacting atoms in a strongly coupled atom-cavity system , Phys. Rev. Lett. 103, 123006 (2009)arXivABSTRACT »We experimentally investigate the spin dynamics of one and two neutral atoms strongly coupled to a high finesse optical cavity. We observe quantum jumps between hyperfine ground states of a single atom. The interaction-induced normal-mode splitting of the atom-cavity system is measured via the atomic excitation. Moreover, we observe the mutual influence of two atoms simultaneously coupled to the cavity mode.
2008
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Controlled insertion and retrieval of atoms coupled to a high-finesse optical resonator, New J. Phys. 10, 073023 (2008)arXivABSTRACT »We experimentally investigate the interaction between one and two atoms and the field of a high-finesse optical resonator. Laser-cooled caesium atoms are transported into the cavity using an optical dipole trap. We monitor the interaction dynamics of a single atom strongly coupled to the resonator mode for several hundred milliseconds by observing the cavity transmission. Moreover, we investigate the position-dependent coupling of one and two atoms by shuttling them through the cavity mode. We demonstrate an alternative method, which suppresses heating effects, to analyze the atom-field interaction by retrieving the atom from the cavity and by measuring its final state.
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Continuous-wave coherent ultraviolet source at 326 nm based on frequency trippling of fiber amplifiers, Opt. Express 16, 16803-16808 (2008)ABSTRACT »We have demonstrated a tunable single frequency source of continuous-wave (CW) coherent ultraviolet (UV) radiation at λ_3ω = 326 nm. Laser light of a tunable diode laser at λ_ω = 977 nm was split and injected into two independent fiber amplifiers yielding 1 W and 0.4 W, respectively. The 1 W branch was resonantly frequency doubled, resulting in 120 mW of useful power at λ_2ω = 488 nm. The third harmonic was generated by summation of the second branch of λ_ω and λ_2ω which were enhanced by a doubly resonant cavity. This light source has TEM_00 character and can be continuously tuned over more than 18 GHz. It is of interest for efficient laser cooling of In and potentially other applications.
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Laser cooling of an indium atomic beam enabled by magnetic fields, Phys. Rev. A 77, 033402 (2008)ABSTRACT »We demonstrate magnetic field enabled optical forces on a neutral indium atomic beam in a light field consisting of five frequencies. The role of dark magnetic ground state sublevels is studied and enables us to cool the atomic beam transversely to near the Doppler limit with laser frequencies tuned above the atomic resonance. The effect of laser cooling can be explained with transient effects in the light potential created by the standing wave light field where the atoms are optically pumped into the dark states and recycled by Larmor precession.
2007
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Cold-Atom Physics Using Ultrathin Optical Fibers: Light-Induced Dipole Forces and Surface Interactions, Phys. Rev. Lett. 99, 163602 (2007)arXivABSTRACT »The strong evanescent field around ultrathin unclad optical fibers bears a high potential for detecting, trapping, and manipulating cold atoms. Introducing such a fiber into a cold-atom cloud, we investigate the interaction of a small number of cold cesium atoms with the guided fiber mode and with the fiber surface. Using high resolution spectroscopy, we observe and analyze light-induced dipole forces, van der Waals interaction, and a significant enhancement of the spontaneous emission rate of the atoms. The latter can be assigned to the modification of the vacuum modes by the fiber.
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Species-selective microwave cooling of a mixture of rubidium and caesium atoms, New J. Phys. 9, 147 (2007)ABSTRACT »We have sympathetically cooled a small sample of 133Cs atoms with 87Rb to below 1 μK. Evaporative cooling was realized with microwave radiation driving the Rb ground-state hyperfine transition. By analysing the sympathetic cooling dynamics, we derive a lower limit of the modulus of the Rb–Cs interspecies triplet s-wave scattering length of 200 a_0. For temperatures below 5 μK we observe strong non-exponential losses of the Cs sample in the presence of the Rb sample.
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Ultra-sensitive surface absorption spectroscopy using sub-wavelength diameter optical fibers, Opt. Express 15, 11952-11958 (2007)arXivABSTRACT »The guided modes of sub-wavelength diameter air-clad optical fibers exhibit a pronounced evanescent field. The absorption of particles on the fiber surface is therefore readily detected via the fiber transmission. We show that the resulting absorption for a given surface coverage can be orders of magnitude higher than for conventional surface spectroscopy. As a demonstration, we present measurements on sub-monolayers of 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) molecules at ambient conditions, revealing the agglomeration dynamics on a second to minutes timescale.
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Quantum information processing using selectively addressed atoms, J. Mod. Opt. 54, 1537-1540 (2007)ABSTRACT »In summary, a much clearer picture is now emerging regarding the various atomic and optical approaches. In this article, the worldwide state of the art in this important area of quantum information processing is discussed. The QGATES project encompassed both theoretical and experimental work in the general areas of trapped neutral atoms, cavity QED and trapped ions.
2006
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An atom-sorting machine, Nature 442, 151 (2006)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.
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Manipulating single atoms, Adv. At. Mol. Opt. Phys. 53, 75 (2006)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.
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Precision preparation of strings of trapped neutral atoms, New J. Phys. 8, 191 (2006)arXivABSTRACT »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.
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Number-triggered loading and collisional redistribution of neutral atoms in a standing wave dipole trap, New J. Phys. 8, 259 (2006)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.
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Resist-assisted atom lithography with group III elements, Appl. Phys. B 85, 487-491 (2006)ABSTRACT »Resist-assisted atom lithography with group III elements, specifically with gallium and indium, is demonstrated. Self-assembled monolayers (SAM) of nonanethiols prepared on thin sputtered gold films were exposed to a beam of neutral gallium and indium atoms through a physical mask. The interaction of the Ga and In atoms with the nonanethiol layer, followed by a wet etching process, creates well defined structures on the gold film, with features below 100 nm. The threshold of the lithographic process was estimated by optical methods and found to be around 3 gallium atoms and 12 indium atoms per thiol molecule. Our experiments suggest that resist-assisted atom lithography can be realized with group III elements and possibly extended to new neutral atomic species.
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Inserting two atoms into a single optical micropotential, Phys. Rev. Lett. 97, 243003 (2006)arXivABSTRACT »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
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Optik, Licht und Laser, 2. überarbeitete und erweiterte Auflage, Teubner, (2005)
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Adiabatic Quantum State Manipulation of Single Trapped Atoms, Phys. Rev. A 71, 031404 (2005)arXivABSTRACT »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.
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Submicrometer position control of single trapped neutral atoms, Phys. Rev. Lett. 95, 033002 (2005)arXivABSTRACT »We optically detect the positions of single neutral cesium atoms stored in a standing wave dipole trap with a sub-wavelength resolution of 143 nm rms. The distance between two simultaneously trapped atoms is measured with an even higher precision of 36 nm rms. We resolve the discreteness of the interatomic distances due to the 532 nm spatial period of the standing wave potential and infer the exact number of trapping potential wells separating the atoms. Finally, combining an initial position detection with a controlled transport, we place single atoms at a predetermined position along the trap axis to within 300 nm rms.
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Complex Light-Mask Generation for Atom Guiding by Time and Frequency Domain Intensity Superposition, Laser Physics 15, 95 (2005)ABSTRACT »We propose to generate a complex light mask for atom nanofabrication by multiplexing light fields sequentially in the time domain or synchronously in the frequency domain. The method effectively superposes intensities rather than electric fields and may be useful for atomic beams at thermal velocity and also at very slow velocities.
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The atom pencil: serial writing in the sub-micrometre domain, Appl. Phys. B 80, 941 (2005)ABSTRACT »The atom pencil we describe here is a versatile tool that writes arbitrary structures by atomic deposition in a serial lithographic process. This device consists of a transversely laser-cooled and collimated cesium atomic beam that passes through a 4-pole atom-flux concentrator and impinges on to micron- and sub-micron-sized apertures. The aperture translates above a fixed substrate and enables the writing of sharp features with sizes down to 280 nm. We have investigated the writing and clogging properties of an atom pencil tip fabricated from silicon oxide pyramids perforated at the tip apex with a sub-micron aperture.
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Tunable Whispering Gallery Mode Resonators for Cavity Quantum Electrodynamics, Phys. Rev. A 72, 031801(R) (2005)arXivABSTRACT »We theoretically study the properties of highly prolate shaped dielectric microresonators. Such resonators sustain whispering gallery modes that exhibit two spatially well separated regions with enhanced field strength. The field per photon on the resonator surface is significantly higher than e.g. for equatorial whispering gallery modes in microsphere resonators with a comparable mode volume. At the same time, the frequency spacing of these modes is much more favorable, so that a tuning range of several free spectral ranges should be attainable. We discuss the possible application of such resonators for cavity quantum electrodynamics experiments with neutral atoms and reveal distinct advantages with respect to existing concepts.
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Analysis of dephasing mechanisms in a standing-wave dipole trap, Phys. Rev. A 72, 023406 (2005)arXivABSTRACT »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.
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Atomic nanofabrication: perspectives for serial and parallel deposition , J. Phys.: Conference Series 19, 118 (2005)ABSTRACT »Recent advances in atomic nanofabrication with laser manipulated atomic beams are discussed with regard to the creation of arbitrary structures.
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Advancing atomic nanolithography: cold atomic Cs beam exposure of alkanethiol self-assembled monolayers, J. Phys.: Conference Series 119, 109 (2005)ABSTRACT »We report the results of a study into the quality of functionalized surfaces for nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent post-etch pattern definition and minimum feature size all depend on the quality of the Au substrate used in atomic nanolithographic experiments. We find sputtered Au substrates yield much smoother surfaces and a higher density of {111} oriented grains than evaporated Au surfaces. A detailed study of the self-assembly mechanism using molecular resolution AFM and STM has shown that the monolayer is composed of domains with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. Exposure of the SAM to an optically-cooled atomic Cs beam traversing a two-dimensional array of submicron material masks ans also standing wave optical masks allowed determination of the minimum average Cs dose (2 Cs atoms per SAM molecule) and the realization of
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Dynamics of atoms interacting via the radiation field in an optical dipole trap, Laser Physics 15, 1189-1203 (2005)ABSTRACT »Theoretical study and computer simulation results for the stochastic dynamics of atoms localized in an optical dipole trap are presented. This dynamics is governed by the optical trap potential, cooling due to the Doppler effect, and heating due to the emission and absorption of virtual photons, i.e., due to the resonant dipole-dipole interactions (RDDI). It is shown that the RDDI becomes essential for closely spaced atoms, but the effect can be significantly improved by irradiating the atoms in the trap with an additional resonance probe laser beam. By varying both the optical dipole trap parameters and intensity of the probe laser field, the role of RDDI in the atomic dynamics in the trap is clarified in detail.
2004
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Neutral Atom Quantum Register, Phys. Rev. Lett. 93, 150501 (2004)arXivABSTRACT »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.
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One- and two-color laser spectroscopy of indium vapor in an all-sapphire cell, Phys. Rev. A 70, 033810 (2004)ABSTRACT »We present saturation and polarization laser spectroscopy experiments of indium vapor with a single color on the 410 nm transition and with two colors at 410 and 451 nm. The spectra observed by polarization spectroscopy are discussed in terms of a quantitative model. The line shapes observed with two-color spectroscopy can phenomenologically be described taking into account hyperfine changing collisions, velocity changing collisions, and dark resonances. As an application, we actively stabilized a 410 nm diode laser on the resonances of saturation and polarization spectroscopy, and obtained long term frequency stabilities in the 100 kHz–1 MHz range.
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Application of electro-optically generated light fields for Raman spectroscopy of trapped Cesium atoms, Appl. Phys. B 78, 711-717 (2004)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
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Atom lithography, Yearbook of Science and Technology, McGraw-Hill, (2003)
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Gerthsen Physik, Springer, Heidelberg, (2003)
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Continued imaging of the transport of a single neutral atom, Opt. Express 11, 3498-3502 (2003)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.
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Optics, Light and Lasers, 1. Auflage, Wiley-VCH, Weinheim , (2003)
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Atomic nanofabrication with complex light fields, Appl. Phys. B 77, 1-9 (2003)ABSTRACT »The method of neutral atom lithography allows one to transfer to a substrate a 2D intensity modulation of an atomic beam imposed by an inhomogeneous light field. The complexity of the pattern depends on the properties of the light field constructed from the superposition of multiple laser beams. For the design of suitable light fields we present a mathematical model with a corresponding numerical simulation of the so-called inverse problem. Furthermore, details of an experiment carried out with a holographically reconstructed light field are discussed.
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Controlled transport of single neutral atom qubits, Proceedings of the 16th ICOLS, (2003)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.
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Coherence properties and quantum state transportation in an optical conveyor belt, Phys. Rev. Lett. 91, 213002 (2003)arXivABSTRACT »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.
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Single atoms in a standing-wave dipole trap, Phys. Rev. A 67, 033403 (2003)arXivABSTRACT »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.
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Atomic nanofabrication: atomic deposition and lithography by laser and magnetic forces, J. Phys. D: Appl. Phys. 36, R17-R38 (2003)ABSTRACT »Atomic deposition on a surface can be controlled at the nanometre scale by means of optical and magnetic forces. Impingement of atoms on the surface can lead to growth of a structured array (direct deposition) or to chemical modifications of the surface (neutral atom lithography). In this report we survey requirements, present the current results, and explore the potential applications of this method of nanofabrication.
2002
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Cold collisions in a high-gradient magneto-optical trap, J. Phys. B: At. Mol. Opt. Phys. 35, 4899 (2002)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.
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Atom Lithography with a Holographic Light Mask, Phys. Rev. Lett. 88, 083601 (2002)ABSTRACT »In atom lithography with optical masks, deposition of an atomic beam on a given substrate is controlled by a standing light-wave field. The lateral intensity distribution of the light field is transferred to the substrate with nanometer scale. We have tailored a complex pattern of this intensity distribution through diffraction of a laser beam from a hologram that is stored in a photorefractive crystal. This method can be extended to superpose 1000 or more laser beams. The method is furthermore applicable during growth processes and thus allows full 3D structuring of suitable materials with periodic and nonperiodic patterns at nanometer scales.
2001
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Laser Physics at the Limits, Springer, Heidelberg, (2001)arXiv
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Deterministic Delivery of a Single Atom, Science 293, 278 (2001)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.
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An optical conveyor belt for single neutral atoms, Appl. Phys. B 73, 819 (2001)arXivABSTRACT »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.
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Magnetic whispering-gallery mirror for atoms, Phys. Rev. A 63, 053405 (2001)ABSTRACT »Videotape with a sinusoidal magnetization of 31 μm wavelength is used to reflect Cs atoms with unit reflectivity in a 75 m/s atomic beam. The atoms serve as a probe, allowing us to measure the magnetic field at the surface. A technique is presented for mounting the videotape so that its surface can be curved to a specific shape or made flexible. We show that such a reflector provides high-quality grazing-incidence atom optics and we demonstrate deflections as large as 23° in a whispering-gallery geometry.
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A single trapped atom: Light-matter interaction at the microscopic level, Ann. Phys. (Leipzig) 10, 9-18 (2001)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.
2000
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Nanoscale focusing of atoms with a pulsed standing wave, Appl. Phys. B 70, 689 (2000)ABSTRACT »We have theoretically and experimentally investigated the focusing properties of a detuned pulsed standing wave onto a beam of neutral atoms. In close analogy to the continuous-wave situation the dipole force leads to a periodic focusing of atoms with a period of λ/2, provided an adiabatic condition is fulfilled. Pulsed laser light is conveniently converted to short wavelengths and hence offers advantages in the application of atom lithography with elements of technological interest having blue or UV resonance lines.
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High-brilliance Zeeman-slowed cesium atomic beam, Phys. Rev. A 61, 013405 (2000)ABSTRACT »We have built a Zeeman-slower apparatus which produces a slow and cold cesium atomic beam. The atomic beam has a mean velocity in the range 35–120 m/s and a high atomic current of more than 2×10^10 cold atoms/s. A small longitudinal velocity spread was achieved by optimizing the termination of the slowing process. The measured value of less than 1 m/s is consistent with a numerical simulation of the slowing process. With a magnetic lens and a tilted two-dimensional optical molasses stage, the slow atomic beam is transversely compressed, collimated, and deflected. We achieve a transverse temperature below the Doppler limit. The brilliance of this beam has been determined to be 7×10^23 atoms s^-1 m^-2 sr^-1. By optical pumping the slow atomic beam can be polarized in the outermost magnetic substates F=4,mF=±4, of the cesium ground state. This brilliant beam is an ideal source for experiments in atom optics and atom lithography.
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GaN blue diode lasers: a spectroscopist's view, Appl. Phys. B 70, 567 (2000)ABSTRACT »We have characterized the spectroscopic properties of one of the first samples of blue-emitting diode lasers based on GaN. With such a laser diode operated inside a standard extended cavity arrangement we find a mode-hop free tuning range of more than 20 GHz and a linewidth of 10 MHz. Doppler-free spectroscopy on an indium atomic beam reveals the isotope shift between the two major indium isotopes as well as efficient optical pumping.
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Single Atoms in an Optical Dipole Trap: Towards a Deterministic Source of Cold Atoms, Phys. Rev. Lett. 85, 3777 (2000)arXivABSTRACT »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.
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Quantum Fluctuations of a Single Trapped Atom: Transient Rabi Oscillations and Magnetic Bistability, IEEE J. of Quantum Electronics 36, 1358 (2000)arXivABSTRACT »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.
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Reflection of cold atoms by a cobalt single crystal, Appl. Phys. B 70, 661 (2000)ABSTRACT »We have demonstrated that a cobalt single crystal can be used to make a remarkably smooth retro-reflector for cold paramagnetic atoms. The crystal is cut so that its surface lies in the (0001) plane and the atoms are reflected by the magnetic field above the surface due to the self-organized pattern of magnetic domains in the material. We find that the reflectivity for suitably polarized atoms exceeds 90% and may well be unity. We use the angular spread of a reflected atom cloud to measure the roughness of the mirror. We find that the angular variation of the equivalent hard reflecting surface is (3.1±0.3°)rms for atoms dropped onto the mirror from a height of 2 cm.
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Counting Cold Collisions, J. Phys. B: At. Mol. Opt. Phys. 33, L135 (2000)arXivABSTRACT »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.
1999
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Optik, Licht und Laser, 1. Auflage, Teubner, (1999)
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Reflection of a slow cesium atomic beam from a naturally magnetized Nd-Fe-B surface, Appl. Phys. B 69, 501 (1999)ABSTRACT »We have demonstrated the partly directed reflection of a slow cesium atomic beam by using the natural magnetic stray field above a Nd-Fe-B surface. From these experiments we determine the reflectivity and a minimum value for the magnetic stray field directly at the surface.
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Efficient magnetic guiding and deflection of atomic beams with moderate velocities, Appl. Phys. B 69, 217 (1999)ABSTRACT »We have studied guidance and deflection of a beam of cesium atoms by a strong toroidal magnetic quadrupole field. The beam guide is made from permanent magnets sustaining a radial field gradient of 2.8 T/cm. Atoms with moderate longitudinal velocities ranging from 30 m/s to 70 m/s were inserted across the 10-mm-diameter aperture of a 24.5° arc with radius 300 mm. We have measured transmission and beam divergence and find good agreement with ray-tracing calculations and analytical estimates. The magnetic beam guide allows for 100% transmission of heavy atoms over large angles.
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Magneto-optical trap as an optical lattice, Phys. Rev. A 61, 013409 (1999)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.
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Light shift of coherent population trapping resonances, Europhys. Lett. 48, 385-389 (1999)ABSTRACT »We have measured the spectral position of the absorption minimum in a coherent population trapping resonance in thermal cesium vapor as a function of light intensity. The dependence of position on intensity is found to be almost linear. We have furthermore studied the dependence of this light shift on neon buffer gas pressure and find a strong reduction for higher pressures. So the addition of a buffer gas not only reduces the linewidth of the resonance but also a very important systematic effect for precision measurements.
1998
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Single-atom dynamics revealed by photon correlations, Phys. Rev. A 58, R1657 (1998)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.
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Atomic Bose-Einstein Condensates: A Model for Macroscopic Quantum Systems, Naturwissenschaften 85, 203 85, 203-218 (1998)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.
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Decoding the dynamics of a single trapped atom from photon correlations, Appl. Phys. B 67, 689 (1998)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.
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Modification of resonance fluorescence and absorption in a lambda system by four-wave mixing, Phys. Rev. A 58, 4235 (1998)ABSTRACT »A universal mechanism destroying coherence in a Λ system driven by two resonant laser fields due to four-photon interactions is analyzed theoretically. It is shown that this mechanism gives rise to novel spectral structures in resonance fluorescence. The “dark resonance” in absorption (dispersion) spectra is affected as well.
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Standing light fields for cold atoms with intrinsically stable and variable time phases, Opt. Comm. 148, 45 (1998)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.
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Selection rules and line strengths of Zeeman-split dark resonances, Phys. Rev. A 58, 196 (1998)ABSTRACT »In a weak magnetic field coherent dark resonances in cesium vapor are split into up to 15 resolved components, depending on field direction and laser polarizations. We find that the selection rules are different for vapor cells with and without buffer gas due to a change in multipolarity of the two-photon coupling. At low laser intensities or sufficiently high buffer-gas pressure optical pumping between different dark resonances can be neglected so that a simple model allows one to calculate the relative line strengths, giving complete agreement with the experimental spectra.
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Experimental realization of coherent dark-state magnetometers , Europhys. Lett. 44, 31 (1998)ABSTRACT »Coherent population trapping resonances in cesium vapor can be used to determine DC flux densities in the range from 1 μT to 1 mT with typically 3·10^−5 relative uncertainty. For fields modulated at a few kHz, we find sensitivities of below 10 pT within 0.5 s integration time. From the signal-to-noise ratio the sensitivity can be extrapolated to 500 fT/√Hz. A quantitative understanding of the lineshape allows to detect DC fields of several nT even when the Zeeman components of the resonance are not resolved.
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Effect of four-photon interactions on coherent population trapping in Lambda-systems, J. Exp. Theor. Phys. 86, 79-92 (1998)ABSTRACT »The resonance fluorescence spectrum of a Λ-system excited by two resonant light fields is calculated using a Markov analysis. Analytical formulas are derived in the strong-field limit within and beyond the rotating wave approximation. It is shown that the resonance fluorescence of the system does not vanish during coherent population trapping. Its spectrum consists of two multiplets which are similar to a triplet in the resonance fluorescence spectrum of a two-level atom and lie at the electronic transition frequencies, together with two triplets located at the frequencies of four-photon processes involving the optical excitation fields. The latter are fundamental in character and impose limits on the lower bound of the dephasing rate for the Raman resonance owing to the effect of radiative decay of the dipole transitions on the dynamics of the ground state. The effect of four-photon dephasing on the absorption spectrum of a Λ-system is analyzed and found to lead to a substantial reduction in the depth of a dip in the absorption spectrum which vanishes as the laser field strength is increased. Zh. Éksp. Teor. Fiz. 113, 144–167 (January 1998)
1997
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Diffraction by cold atoms, Opt. Comm. 145, 57 (1997)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.
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Magnetostatic traps for charged and neutral particles, Hyperfine Interactions 109, 281-292 (1997)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.
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