406 research outputs found
Revealing quantum statistics with a pair of distant atoms
Quantum statistics have a profound impact on the properties of systems
composed of identical particles. In this Letter, we demonstrate that the
quantum statistics of a pair of identical massive particles can be probed by a
direct measurement of the exchange symmetry of their wave function even in
conditions where the particles always remain spatially well separated and thus
the exchange contribution to their interaction energy is negligible. We present
two protocols revealing the bosonic or fermionic nature of a pair of particles
and discuss possible implementations with a pair of trapped atoms or ions.Comment: 4+13 pages, v2 corresponds to the version published by PR
Beyond the Spin Model Approximation for Ramsey Spectroscopy
Ramsey spectroscopy has become a powerful technique for probing
non-equilibrium dynamics of internal (pseudospin) degrees of freedom of
interacting systems. In many theoretical treatments, the key to understanding
the dynamics has been to assume the external (motional) degrees of freedom are
decoupled from the pseudospin degrees of freedom. Determining the validity of
this approximation -- known as the spin model approximation -- is complicated,
and has not been addressed in detail. Here we shed light in this direction by
calculating Ramsey dynamics exactly for two interacting spin-1/2 particles in a
harmonic trap. We focus on -wave-interacting fermions in quasi-one and
two-dimensional geometries. We find that in 1D the spin model assumption works
well over a wide range of experimentally-relevant conditions, but can fail at
time scales longer than those set by the mean interaction energy. Surprisingly,
in 2D a modified version of the spin model is exact to first order in the
interaction strength. This analysis is important for a correct interpretation
of Ramsey spectroscopy and has broad applications ranging from precision
measurements to quantum information and to fundamental probes of many-body
systems
Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields
We have observed Feshbach resonances for 133Cs atoms in two different
hyperfine states at ultra-low static magnetic fields by using an atomic
fountain clock. The extreme sensitivity of our setup allows for high
signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have
reproduced these resonances using coupled-channels calculations which are in
excellent agreement with our measurements. We justify that these are s-wave
resonances involving weakly-bound states of the triplet molecular Hamiltonian,
identify the resonant closed channels, and explain the observed multi-peak
structure. We also describe a model which precisely accounts for the
collisional processes in the fountain and which explains the asymmetric shape
of the observed Feshbach resonances in the regime where the kinetic energy
dominates over the coupling strength.Comment: 5 pages, 4 figures, 1 tabl
Collisionally Induced Atomic Clock Shifts and Correlations
We develop a formalism to incorporate exchange symmetry considerations into
the calculation of collisional frequency shifts and blackbody radiation effects
for atomic clock transitions using a density matrix formalism. The formalism is
developed for both fermionic and bosonic atomic clocks. Results for a finite
temperature Sr () atomic clock in a magic
wavelength optical lattice are presented.Comment: 11 pages, 9 figures. Physical Review A (in press
Metalloporphyrins on Oxygen-Passivated Iron: Conformation and Order Beyond the First Layer
On-surface metal porphyrins can undergo electronic and conformational changes
that play a crucial role in determining the chemical reactivity of the
molecular layer. Therefore, understanding those properties is pivotal for the
design and implementation of organic-based devices. Here, by means of
photoemission orbital tomography supported by density functional theory
calculations, we investigate the electronic and geometrical structure of two
metallated tetraphenyl porphyrins (MTPPs), namely ZnTPP and NiTPP, adsorbed on
the oxygen-passivated Fe(100)-p(1x1)O surface. Both molecules weakly interact
with the surface as no charge transfer is observed. In the case of ZnTPP our
data correspond to those of moderately distorted molecules, while NiTPP
exhibits a severe saddle-shape deformation. From additional experiments on
NiTPP multilayer films, we conclude that this distortion is a consequence of
the interaction with the substrate, as the NiTPP macrocycle of the second layer
turns out to be flat. We further find that distortions in the MTPP macrocycle
are accompanied by an increasing energy gap between the highest occupied
molecular orbitals (HOMO and HOMO-1). Our results demonstrate that
photoemission orbital tomography can simultaneously probe the energy level
alignment, the azimuthal orientation, and the adsorption geometry of complex
aromatic molecules even in the multilayer regime
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