Sympathetic Wigner function tomography of a dark trapped ion

A protocol is provided to reconstruct the Wigner function for the motional state of a trapped ion via fluorescence detection on another ion in the same trap. This "sympathetic tomography" of a dark ion without optical transitions suitable for state measurements is based on the mapping of its motional state onto one of the collective modes of the ion pair. The quantum state of this vibrational eigenmode is subsequently measured through sideband excitation of the bright ion. Physical processes to implement the desired state transfer and read-out are derived, and the accomplishment of the scheme for different mass ratios is evaluated.Comment: 8 pages, 5 figure

Geometric quantum gate for trapped ions based on optical dipole forces induced by Gaussian laser beams

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.Comment: 10 pages, 4 figure

Experimental investigation of ultracold atom-molecule collisions

Ultracold collisions between Cs atoms and Cs2 dimers in the electronic ground state are observed in an optically trapped gas of atoms and molecules. The Cs2 molecules are formed in the triplet ground state by cw-photoassociation through the outer well of the 0g-(P3/2) excited electronic state. Inelastic atom-molecule collisions converting internal excitation into kinetic energy lead to a loss of Cs2 molecules from the dipole trap. Rate coefficients are determined for collisions involving Cs atoms in either the F=3 or F=4 hyperfine ground state and Cs2 molecules in either highly vibrationally excited states (v'=32-47) or in low vibrational states (v'=4-6) of the a ^3 Sigma_u^+ triplet ground state. The rate coefficients beta ~10^{-10} cm^3/s are found to be largely independent of the vibrational and rotational excitation indicating unitary limited cross sections.Comment: 4 pages, 3 figures, submitted for publicatio

The X1Σ+^1\Sigma^+ and a3Σ+^3\Sigma^+ states of LiCs studied by Fourier-transform spectroscopy

We present the first high-resolution spectroscopic study of LiCs. LiCs is formed in a heat pipe oven and studied via laser-induced fluorescence Fourier-transform spectroscopy. By exciting molecules through the X$^1\Sigma^+$-B$^1\Pi$ and X$^1\Sigma^+$-D$^1\Pi$ transitions vibrational levels of the X$^1\Sigma^+$ ground state have been observed up to 3cm^{-1} below the dissociation limit enabling an accurate construction of the potential. Furthermore, rovibrational levels in the a$^3\Sigma^+$ triplet ground state have been observed because the excited states obtain sufficient triplet character at the corresponding excited atomic asymptote. With the help of coupled channels calculations accurate singlet and triplet ground state potentials were derived reaching the atomic ground state asymptote and allowing first predictions of cold collision properties of Li + Cs pairs.Comment: 10 pages, 5 figures. Submitted for publicatio

Lifetime measurement of the metastable 3d 2D5/2 state in the 40Ca+ ion using the shelving technique on a few-ion string

We present a measurement of the lifetime of the metastable 3d 2D5/2 state in the 40Ca+ ion, using the so-called shelving technique on a string of five Doppler laser-cooled ions in a linear Paul trap. A detailed account of the data analysis is given, and systematic effects due to unwanted excitation processes and collisions with background gas atoms are discussed and estimated. From a total of 6805 shelving events, we obtain a lifetime tau=1149+/-14(stat.)+/-4(sys.)ms, a result which is in agreement with the most recent measurements.Comment: 10 pages, 7 figures. Submitted for publicatio

Trapped-Ion Quantum Logic Utilizing Position-Dependent ac Stark Shifts

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.Comment: 5 pages, 4 figures. Submitted to Physical Review Letter

Tumor dosimetry using 177Lu: influence of background activity, measurement method and reconstruction algorithm

Abstract Background Image-based tumor dosimetry after radionuclide therapy, using the isotope 177Lu, finds application e.g., for tumor-to-organ dose comparison and for dose response evaluation. When the tumor extent is not much larger than the image resolution, and when 177Lu is found in nearby organs or other tumors, an accurate determination of tumor dose is particularly challenging. Here a quantitative evaluation of three different methods for determining the 177Lu activity concentration in a phantom is performed, and the dependence on a variety of parameters is described. The phantom (NEMA IEC body phantom) has spheres of different size in a background volume, and sphere-to-background 177Lu activity concentration ratios of infinity, 9.5, 5.0 and 2.7 are applied. The methods are simple to implement and well-known from the literature. They are based on (1) a large VOI encompassing the whole sphere, without background activity and with volume information from other sources, (2) a small VOI located in the sphere center, and (3) a VOI consisting of voxels with voxel value above a certain percentage of the maximum voxel value. Results The determined activity concentration varies significantly with sphere size, sphere-to-background ratio, SPECT reconstruction method and method for determining the concentration. Based on the phantom study, criteria are identified under which the activity concentration can be determined with a maximal error of 40% even in the presence of background activity. Conclusions Tumor dosimetry is feasible in the presence of background activity using the above-mentioned methods, provided appropriate SPECT reconstructions are applied and tumors are selected for dosimetry analysis according to the following criteria for the three methods: (1) solitary tumor with diameter > 15 mm, (2) tumor diameter > 30 mm and tumor-to-background ratio > 2, and (3) tumor diameter > 30 mm and tumor-to-background ratio > 3