7 research outputs found
State-selective transport of single neutral atoms
The present work investigates the state-selective transport of single neutral cesium atoms in a one-dimensional optical lattice. It demonstrates experimental applications of this transport, including a single atom interferometer, a quantum walk and controlled two-atom collisions. The atoms are stored one by one in an optical lattice formed by a standing wave dipole trap. Their positions are determined with sub-micrometer precision, while atom pair separations are reliably inferred down to neighboring lattice sites using real-time numerical processing. Using microwave pulses in the presence of a magnetic field gradient, the internal qubit states, encoded in the hyperfine levels of the atoms, can be separately initialized and manipulated. This allows us to perform arbitrary single-qubit operations and prepare arbitrary patterns of atoms in the lattice with single-site precision. Chapter 1 presents the experimental setup for trapping a small number of cesium atoms in a one-dimensional optical lattice. Chapter 2 is devoted to fluorescence imaging of atoms, discussing the imaging setup, numeric methods and their performance in detail. Chapter 3 focuses on engineering of internal states of trapped atoms in the lattice using optical methods and microwave radiation. It provides a detailed investigation of coherence properties of our experimental system. Finally manipulation of individual atoms with almost single-site resolution and preparation of regular strings of atoms with predefined distances are presented. In Chapter 4, basic concepts, the experimental realization and the performance of the state-selective transport of neutral atoms over several lattice sites are presented and discussed in detail. Coherence properties of this transport are investigated in Chapter 5, using various two-arms single atom interferometer sequences in which atomic matter waves are split, delocalized, merged and recombined on the initial lattice site, while the interference contrast and the accumulated phase difference are measured. By delocalizing a single atom over several lattice sites, possible spatial inhomogeneities of fields along the lattice axis in the trapping region are probed. In Chapter 6, experimental realization of a discrete time quantum walk on a line with single optically trapped atoms is presented as an advanced application of multiple path quantum interference in the context of quantum information processing. Using this simple example of a quantum walk, fundamental properties of and differences between the quantum and classical regimes are investigated and discussed in detail. Finally, by combining preparation of atom strings, position-dependent manipulation of qubit states and state-selective transport, in Chapter 7, two atoms are deterministically brought together into contact, forming a starting point for investigating two-atom interactions on the most fundamental level. Future prospects and suggestions are finally presented in Chapter 8
Electron spectra close to a metal-to-insulator transition
A high-resolution investigation of the electron spectra close to the
metal-to-insulator transition in dynamic mean-field theory is presented. An
all-numerical, consistent confirmation of a smooth transition at zero
temperature is provided. In particular, the separation of energy scales is
verified. Unexpectedly, sharp peaks at the inner Hubbard band edges occur in
the metallic regime. They are signatures of the important interaction between
single-particle excitations and collective modes.Comment: RevTeX 4, 4 pages, 4 eps figures; published versio
Imprinting Patterns of Neutral Atoms in an Optical Lattice using Magnetic Resonance Techniques
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 of 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.Comment: 9 pages, 7 figure
Direct Observation and Analysis of Spin Dependent Transport of Single Atoms in a 1D Optical Lattice
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 causes displacement of the
- and -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.Comment: 5 pages, 4 figure
Single-Particle Dynamics in the Vicinity of the Mott-Hubbard Metal-to-Insulator Transition
The single-particle dynamics close to a metal-to-insulator transition induced
by strong repulsive interaction between the electrons is investigated. The
system is described by a half-filled Hubbard model which is treated by dynamic
mean-field theory evaluated by high-resolution dynamic density-matrix
renormalization. We provide theoretical spectra with momentum resolution which
facilitate the comparison to photoelectron spectroscopy.Comment: 22 pages, 24 figures, comprehensive high-resolution study of single
electron dynamics around a Mott metal-insulator transition, with momentum
resolved spectral densities; slight changes due to referees' suggestion