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Search Results: 1 - 10 of 44871 matches for " Michael Drewsen "
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Trapped-Ion Quantum Logic Utilizing Position-Dependent ac Stark Shifts
Peter Staanum,Michael Drewsen
Physics , 2002, DOI: 10.1103/PhysRevA.66.040302
Abstract: We present a scheme utilizing position-dependent ac Stark shifts for doing quantum logic with trapped ions. By a proper choice of direction, position and size, as well as power and frequency of a far-off-resonant Gaussian laser beam, specific ac Stark shifts can be assigned to the individual ions, making them distinguishable in frequency-space. In contrast to previous all-optical based quantum gates with trapped ions, the present scheme enables individual addressing of single ions and selective addressing of any pair of ions for two-ion quantum gates, without using tightly focused laser beams. Furthermore, the decoherence rate due to off-resonant excitations can be made negligible as compared with other sources of decoherence.
Adiabatic cooling of a single trapped ion
Gregers Poulsen,Michael Drewsen
Physics , 2012,
Abstract: We present experimental results on adiabatic cooling of a single 40Ca+ ion in a linear radiofrequency trap. After a period of laser cooling, the secular frequency along the rf-field-free axis is adiabatically lowered by nearly a factor of eight from 583 kHz to 75 kHz. For an ion originally Doppler laser cooled to a temperature of 0.65 +/- 0.03 mK, a temperature of 87 +/- 7 \mu K is measured after the adiabatic expansion. Applying the same adiabatic cooling procedure to a single sideband cooled ion in the ground state (P0 = 0.978 +/- 0.002) resulted in a final ground state occupation of 0.947 +/- 0.005. Both results are in excellent agreement with an essentially fully adiabatic behavior. The results have a wide range of perspectives within such diverse fields as ion based quantum information science, high resolution molecular ion spectroscopy and ion chemistry at ultra-low temperatures.
The rotational temperature of polar molecular ions in Coulomb crystals
Anders Bertelsen,Solvejg J?rgensen,Michael Drewsen
Physics , 2005, DOI: 10.1088/0953-4075/39/5/L02
Abstract: With MgH^+ ions as a test case, we investigate to what extent the rotational motion of smaller polar molecular ions sympathetically cooled into Coulomb crystals in linear Paul traps couples to the translational motions of the ion ensemble. By comparing results obtained from rotational state-selective resonance-enhanced photo-dissociation experiments with data from theoretical simulations, we conclude that the effective rotational temperature exceeds the translational temperature (< 100 mK) by more than two orders of magnitude, indicating a very weak coupling. In fact, the experimental results are consistent with the rotational temperature being in thermal equilibrium with the surrounding environment at ~300 K.
Geometric quantum gate for trapped ions based on optical dipole forces induced by Gaussian laser beams
Peter Staanum,Michael Drewsen,Klaus Moelmer
Physics , 2004, DOI: 10.1103/PhysRevA.70.052327
Abstract: We present an implementation of quantum logic gates via internal state dependent displacements of ions in a linear Paul trap caused by optical dipole forces. Based on a general quantum analysis of the system dynamics we consider specific implementations with alkaline earth ions. For experimentally realistic parameters gate infidelities as low as $10^{-4}$ can be obtained.
Analysis of a photon number resolving detector based on an ion Coulomb crystal inside an optical cavity
Christoph Clausen,Nicolas Sangouard,Michael Drewsen
Physics , 2012, DOI: 10.1088/1367-2630/15/2/025021
Abstract: The ability to detect single photons with high efficiency is a crucial requirement for various quantum information applications. By combining the storage process of a quantum memory for photons with fluorescence-based quantum state measurement, it is in principle possible to achieve high efficiency photon counting in large ensembles of atoms. The large number of atoms can, however, pose significant problems in terms of noise stemming from imperfect initial state preparation and off-resonant fluorescence. We propose a concrete implementation of a photon number resolving detector based on an ion Coulomb crystal inside a moderately high-finesse optical cavity. The cavity enhancement leads to an effective optical depth of 15 for a finesse of 3000 with only about 1500 ions interacting with the light field. We show that these values allow for essentially noiseless detection with an efficiency larger than 90%. Moderate experimental parameters allow for repetition rates of about 5 kHz, limited by the time needed for fluorescence collection. Potential applications are discussed.
Probing isotope effects in chemical reactions using single ions
Peter F. Staanum,Klaus Hoejbjerre,Roland Wester,Michael Drewsen
Physics , 2008, DOI: 10.1103/PhysRevLett.100.243003
Abstract: Isotope effects in reactions between Mg+ in the 3p 2P3/2 excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only ~250 reactions with HD, the branching ratio between formation of MgD+ and MgH+ is found to be larger than 5. From additional 65 reactions with H2 and D2 we find that the overall decay probability of the intermediate MgH2+, MgHD+ or MgD2+ complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well-suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.
Direct imaging of thermally excited metastable structures of ion Coulomb clusters
Michael Drewsen,Thierry Matthey,Anders Mortensen,Jan Petter Hansen
Physics , 2012,
Abstract: Coulomb crystallisation of large ensembles of ions has in the past years been intensively studied experimentally with many spectacular results of relevance to infinite systems in one-, two-, and three-dimensions.While strings of a few ions have proven to be very attractive objects in quantum information processing, larger Coulomb crystals have very recently found applications within other aspects the dynamics of quantum systems. Smaller finite ensembles of cold identical charged particles confined by a harmonic potential furthermore constitute very special types of clusters due to the pure repulsive long-range inter-particle forces. Here, we report on the direct imaging of metastable structures of Coulomb clusters consisting of a few thousands confined and laser-cooled 40Ca+ ions. The observations are attributed to structural excitations due to finite temperatures, a feature likely to appear in clusters of short-range interacting particles, but yet not observed directly.
Profiling of micrometer sized laser beams in restricted volumes
Yevhen Miroshnychenko,Otto Nielsen,Aske Thorsen,Michael Drewsen
Physics , 2012, DOI: 10.1364/AO.51.002341
Abstract: We present a method for determining the 3D intensity distribution of directed laser radiation with micrometer resolution in restricted volumes. Our method is based on in-coupling and guiding properties of optical fibers, with the current version requiring only few hundred micrometers. We characterize the performance of the method and experimentally demonstrate profiling of micrometer sized laser beams. We discuss the limiting factors and routes towards a further increase of the resolution and beam profiling in even more restricted volumes. Finally, as an application example, we present profiling of laser beams inside a micro ion trap with integrated optical fibers.
Femtosecond wavepacket interferometry using the rotational dynamics of a trapped cold molecular ion
J. Martin Berglund,Michael Drewsen,Christiane P. Koch
Physics , 2014, DOI: 10.1088/1367-2630/17/2/025007
Abstract: A Ramsey-type interferometer is suggested, employing a cold trapped ion and two time-delayed off-resonant femtosecond laser pulses. The laser light couples to the molecular polarization anisotropy, inducing rotational wavepacket dynamics. An interferogram is obtained from the delay dependent populations of the final field-free rotational states. Current experimental capabilities for cooling and preparation of the initial state are found to yield an interferogram visibility of more than 80\%. The interferograms can be used to determine the polarizability anisotropy with an accuracy of about $\pm 2\%$, respectively $\pm 5\%$, provided the uncertainty in the initial populations and measurement errors are confined to within the same limits.
Two-step Doppler cooling of a three-level ladder system with an intermediate metastable level
Caroline Champenois,Gaetan Hagel,Martina Knoop,Marie Houssin,Cedric Zumsteg,Fernande Vedel,Michael Drewsen
Physics , 2007, DOI: 10.1103/PhysRevA.77.033411
Abstract: Doppler laser cooling of a three-level ladder system using two near-resonant laser fields is analyzed in the case of the intermediate level being metastable while the upper level is short-lived. Analytical as well as numerical results for e.g. obtainable scattering rates and achievable temperatures are presented. When appropriate, comparisons with two-level single photon Doppler laser cooling is made. These results are relevant to recent experimental Doppler laser cooling investigations addressing intercombination lines in alkali-earth metal atoms and quadrupole transitions in alkali-earth metal ions.
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