76,848 research outputs found
A ring trap for ultracold atoms
We propose a new kind of toroidal trap, designed for ultracold atoms. It
relies on a combination of a magnetic trap for rf-dressed atoms, which creates
a bubble-like trap, and a standing wave of light. This new trap is well suited
for investigating questions of low dimensionality in a ring potential. We study
the trap characteristics for a set of experimentally accessible parameters. A
loading procedure from a conventional magnetic trap is also proposed. The
flexible nature of this new ring trap, including an adjustable radius and
adjustable transverse oscillation frequencies, will allow the study of
superfluidity in variable geometries and dimensionalities.Comment: 4 figures, 10 pages ; the order of the sections has been changed ; to
appear in Phys. Rev.
Phase and micromotion of Bose-Einstein condensates in a time-averaged ring trap
Rapidly scanning magnetic and optical dipole traps have been widely utilised
to form time-averaged potentials for ultracold quantum gas experiments. Here we
theoretically and experimentally characterise the dynamic properties of
Bose-Einstein condensates in ring-shaped potentials that are formed by scanning
an optical dipole beam in a circular trajectory. We find that unidirectional
scanning leads to a non-trivial phase profile of the condensate that can be
approximated analytically using the concept of phase imprinting. While the
phase profile is not accessible through in-trap imaging, time-of-flight
expansion manifests clear density signatures of an in-trap phase step in the
condensate, coincident with the instantaneous position of the scanning beam.
The phase step remains significant even when scanning the beam at frequencies
two orders of magnitude larger than the characteristic frequency of the trap.
We map out the phase and density properties of the condensate in the scanning
trap, both experimentally and using numerical simulations, and find excellent
agreement. Furthermore, we demonstrate that bidirectional scanning eliminated
the phase gradient, rendering the system more suitable for coherent matter wave
interferometry.Comment: 10 pages, 7 figure
Probing the exchange statistics of one-dimensional anyon models
We propose feasible scenarios for revealing the modified exchange statistics
in one-dimensional anyon models in optical lattices based on an extension of
the multicolor lattice-depth modulation scheme introduced in [{Phys. Rev. A 94,
023615 (2016)}]. We show that the fast modulation of a two-component fermionic
lattice gas in the presence a magnetic field gradient, in combination with
additional resonant microwave fields, allows for the quantum simulation of
hardcore anyon models with periodic boundary conditions. Such a semi-synthetic
ring set-up allows for realizing an interferometric arrangement sensitive to
the anyonic statistics. Moreover, we show as well that simple expansion
experiments may reveal the formation of anomalously bound pairs resulting from
the anyonic exchange.Comment: 8 pages, 9 figure
One- and two-atom states in a rotating ring lattice
We study the states of one and two atoms in a rotating ring lattice in a
Hubbard type tight-binding model. The model is developed carefully from basic
principles in order to properly identify the physical observables. The
one-particle ground state may be degenerate and represent a finite flow
velocity depending on the parity of the number of lattice sites, the sign of
the tunneling matrix element, and the rotation speed of the lattice. Variation
of the rotation speed may be used to control one-atom states, and leads to
peculiar behaviors such as wildly different phase and group velocities for an
atom. Adiabatic variation of the rotation speed of the lattice may also be used
to control the state of a two-atom lattice dimer. For instance, at a suitably
chosen rotation speed both atoms are confined to the same lattice site.Comment: Very close to the submitted versio
Quasiparticles in Neon using the Faddeev Random Phase Approximation
The spectral function of the closed-shell Neon atom is computed by expanding
the electron self-energy through a set of Faddeev equations. This method
describes the coupling of single-particle degrees of freedom with correlated
two-electron, two-hole, and electron-hole pairs. The excitation spectra are
obtained using the Random Phase Approximation, rather than the Tamm-Dancoff
framework employed in the third-order algebraic diagrammatic contruction
[ADC(3)] method. The difference between these two approaches is studied, as
well as the interplay between ladder and ring diagrams in the self-energy.
Satisfactory results are obtained for the ionization energies as well as the
energy of the ground state with the Faddeev-RPA scheme that is also appropriate
for the high-density electron gas.Comment: Revised manuscript. The working equations of the Faddeev-RPA method
are included in the Appendi
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Gas-Phase Synthesis of Triphenylene (C18 H12 ).
For the last decades, the hydrogen-abstraction-acetylene-addition (HACA) mechanism has been widely invoked to rationalize the high-temperature synthesis of PAHs as detected in carbonaceous meteorites (CM) and proposed to exist in the interstellar medium (ISM). By unravelling the chemistry of the 9-phenanthrenyl radical ([C14 H9 ]. ) with vinylacetylene (C4 H4 ), we present the first compelling evidence of a barrier-less pathway leading to a prototype tetracyclic PAH - triphenylene (C18 H12 ) - via an unconventional hydrogen abstraction-vinylacetylene addition (HAVA) mechanism operational at temperatures as low as 10 K. The barrier-less, exoergic nature of the reaction reveals HAVA as a versatile reaction mechanism that may drive molecular mass growth processes to PAHs and even two-dimensional, graphene-type nanostructures in cold environments in deep space thus leading to a better understanding of the carbon chemistry in our universe through the untangling of elementary reactions on the most fundamental level
Readout of the atomtronic quantum interference device
A Bose-Einstein condensate confined in ring shaped lattices interrupted by a
weak link and pierced by an effective magnetic flux defines the atomic
counterpart of the superconducting quantum interference device: the atomtronic
quantum interference device (AQUID). In this paper, we report on the detection
of current states in the system through a self-heterodyne protocol. Following
the original proposal of the NIST and Paris groups, the ring-condensate
many-body wave function interferes with a reference condensate expanding from
the center of the ring. We focus on the rf-AQUID which realizes effective qubit
dynamics. Both the Bose-Hubbard and Gross-Pitaevskii dynamics are studied. For
the Bose-Hubbard dynamics, we demonstrate that the self-heterodyne protocol can
be applied, but higher-order correlations in the evolution of the interfering
condensates are measured to readout of the current states of the system. We
study how states with macroscopic quantum coherence can be told apart analyzing
the noise in the time of flight of the ring condensate
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