659 research outputs found
Ramsey interferometry in three-level and five-level systems of Bose-Einstein condensates
Our work here presents the analytical expressions for a typical Ramsey
interferometric sequence for a three- and a five-level system. The analytical
expressions are derived starting from the first principals of unitary time
evolution operators. We focus on the three- and five-level systems because we
propose a novel Ramsey interferometer created by a trapped two-state
Bose-Einstein Condensate driven by dipole oscillations and gravitational sag.
It involves the atoms in states and of the ground state. Though the interferometer focusses on the
two-levels, the experimental readouts involve all the five states in
hyperfine manifold. Therefore, the analytical derivation was first tested for
three-levels and then expanded to five-levels. We developed the expressions for
five-levels for greater analytical accuracy of the experimental scenario. This
work provides a step-by-step outline for the derivation and methodology for the
analytical expressions. These analytical formulae denote the population
variation during Rabi and Ramsey oscillations for each state as well as the
overall average for both the three- and five-level cases. The expressions are
derived within the rotating wave approximation (RWA) under the equal Rabi
condition. Further, by following the derivation methodology, these analytical
expressions can be easily expanded for Ramsey sequences with unequal pulses,
and Ramsey sequences with spin echo techniques.Comment: 19 pages, 7 figure
Dynamics of reflection of ultracold atoms from a periodic 1D magnetic lattice potential
We report on an experimental study of the dynamics of the reflection of
ultracold atoms from a periodic one-dimensional magnetic lattice potential. The
magnetic lattice potential of period 10 \textmu m is generated by applying a
uniform bias magnetic field to a microfabricated periodic structure on a
silicon wafer coated with a multilayered TbGdFeCo/Cr magneto-optical film. The
effective thickness of the magnetic film is about 960 nm. A detailed study of
the profile of the reflected atoms as a function of externally induced periodic
corrugation in the potential is described. The effect of angle of incidence is
investigated in detail. The experimental observations are supported by
numerical simulations.Comment: 15 pages, 11 figure
Trapping ultracold atoms at 100 nm from a chip surface in a 0.7-micrometer-period magnetic lattice
We report the trapping of ultracold 87Rb atoms in a 0.7 micron-period 2D
triangular magnetic lattice on an atom chip. The magnetic lattice is created by
a lithographically patterned magnetic Co/Pd multilayer film plus bias fields.
Rubidium atoms in the F=1, mF=-1 low-field seeking state are trapped at
estimated distances down to about 100 nm from the chip surface and with
calculated mean trapping frequencies as high as 800 kHz. The measured lifetimes
of the atoms trapped in the magnetic lattice are in the range 0.4 - 1.7 ms,
depending on distance from the chip surface. Model calculations suggest the
trap lifetimes are currently limited mainly by losses due to surface-induced
thermal evaporation following loading of the atoms from the Z-wire trap into
the very tight magnetic lattice traps, rather than by fundamental loss
processes such as surface interactions, three-body recombination or spin flips
due to Johnson magnetic noise. The trapping of atoms in a 0.7 micrometer-period
magnetic lattice represents a significant step towards using magnetic lattices
for quantum tunneling experiments and to simulate condensed matter and
many-body phenomena in nontrivial lattice geometries.Comment: 11 pages, 7 figure
THE PROBLEM OF RUSSIAN POST-REVOLUTIONARY EMIGRATION IN THE CONTEXT OF THE INTERNATIONAL POSITION OF THE SOVIET STATE IN THE FIRST HALF OF THE 1920S
Aim. To consider the Soviet perception of Russian post-revolutionary emigration in the context of the key foreign policy challenges to the Soviet Country of the first half of the 1920s.Methodology. On the basis of the principles of historism and scientific objectivity, the authors analyzed a number of archival and official Soviet documents, as well as parts of the memoirs and journalistic heritage of the Russia Abroad related to the research.Results. It is concluded that during this period the Bolsheviks considered the post-revolutionary emigration as one of the biggest threats to the security of the young Soviet state.Research implications. The article introduced for the first time into the scientific circulation some archival documents that give a more detailed idea of the formation of the Soviet position regarding the plans of F. Nansen for a large-scale repatriation of Russian emigrants to their homeland in the 1920s.</html
Radiofrequency spectroscopy of a linear array of Bose-Einstein condensates in a magnetic lattice
We report site-resolved radiofrequency spectroscopy measurements of
Bose-Einstein condensates of 87Rb atoms in about 100 sites of a one-dimensional
10 micron-period magnetic lattice produced by a grooved magnetic film plus bias
fields. Site-to-site variations of the trap bottom, atom temperature,
condensate fraction and chemical potential indicate that the magnetic lattice
is remarkably uniform, with variations in trap bottoms of only +/- 0.4 mG. At
the lowest trap frequencies (radial and axial frequencies 1.5 kHz and 260 Hz,
respectively), temperatures down to 0.16 microkelvin are achieved in the
magnetic lattice and at the smallest trap depths (50 kHz) condensate fractions
up to 80% are observed. With increasing radial trap frequency (up to 20 kHz, or
aspect ratio up to about 80) large condensate fractions persist and the highly
elongated clouds approach the quasi-1D Bose gas regime. The temperature
estimated from analysis of the spectra is found to increase by a factor of
about five which may be due to suppression of rethermalising collisions in the
quasi-1D Bose gas. Measurements for different holding times in the lattice
indicate a decay of the atom number with a half-life of about 0.9 s due to
three-body losses and the appearance of a high temperature (about 1.5
microkelvin) component which is attributed to atoms that have acquired energy
through collisions with energetic three-body decay products
Magnetic Lattices for Ultracold Atoms
This article reviews the development in our laboratory of magnetic lattices comprising periodic arrays of magnetic microtraps created by patterned magnetic films to trap periodic arrays of ultracold atoms. Recent achievements include the realisation of multiple Bose-Einstein condensates in a 10 m-period one-dimensional magnetic lattice; the fabrication of sub-micron-period square and triangular magnetic lattice structures suitable for quantum tunnelling experiments; the trapping of ultracold atoms in a sub-micron-period triangular magnetic lattice; and a proposal to use long-range interacting Rydberg atoms to achieve spin-spin interactions between sites in a large-spacing magnetic lattice
Dynamical properties of S-gap shifts and other shift spaces
We study the dynamical properties of certain shift spaces. To help study these properties we introduce two new classes of shifts, namely boundedly supermultiplicative (BSM) shifts and balanced shifts. It turns out that any almost specified shift is both BSM and balanced, and any balanced shift is BSM. However, as we will demonstrate, there are examples of shifts which are BSM but not balanced. We also study the measure theoretic properties of balanced shifts. We show that a shift space admits a Gibbs state if and only if it is balanced. Restricting ourselves to S-gap shifts, we relate certain dynamical properties of an S-gap shift to combinatorial properties from expansions in non-integer bases. This identification allows us to use the machinery from expansions in non-integer bases to give straightforward constructions of S -gap shifts with certain desirable properties. We show that for any q∈(0,1) there is an S-gap shift which has the specification property and entropy q . We also use this identification to address the question, for a given q∈(0,1), how many S-gap shifts exist with entropy q? For certain exceptional values of q there is a unique S-gap shift with this entropy
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