181 research outputs found
Exact Eigenstates and Magnetic Response of Spin-1 and Spin-2 Vectorial Bose-Einstein Condensates
The exact eigenspectra and eigenstates of spin-1 and spin-2 vectorial
Bose-Einstein condensates (BECs) are found, and their response to a weak
magnetic field is studied and compared with their mean-field counterparts.
Whereas mean-field theory predicts the vanishing population of the zero
magnetic-quantum-number component of a spin-1 antiferromagnetic BEC, the
component is found to become populated as the magnetic field decreases. The
spin-2 BEC exhibits an even richer magnetic response due to quantum correlation
between 3 bosons.Comment: 5 pages, no figures. LaTeX20
Π Π½Π΅ΠΎΠ±Ρ ΠΎΠ΄ΠΈΠΌΠΎΡΡΠΈ ΠΏΡΠΎΡΠ»Π΅ΠΆΠΈΠ²Π°Π½ΠΈΡ ΠΠ°Π»Π΅ΠΉΡΠΊΠΎ-ΠΠ°ΡΠ°ΡΡΠ½ΡΠΊΠΎΠ³ΠΎ ΡΠ°Π·Π»ΠΎΠΌΠ° Π² ΠΏΡΠ΅Π΄Π΅Π»Π°Ρ ΠΠΎΡΡΠ΅Π²ΠΎΡΠ½ΠΎΠ³ΠΎ ΠΊΡΡΠΆΠ°
In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique a new generation of laser sources for aerospace applications is designed. In these laser systems solder technique replaces the glued and bolted connections between optical component, mount and base plate. Alignment precision in the arc second range and realization of long term stability of every single part in the laser system is the main challenge. At the Fraunhofer Institute for Laser Technology ILT a soldering and mounting technique has been developed for high precision packaging. The specified environmental boundary conditions (e.g. a temperature range of -40 Β°C to +50 Β°C) and the required degrees of freedom for the alignment of the components have been taken into account for this technique. In general the advantage of soldering compared to gluing is that there is no outgassing. In addition no flux is needed in our special process. The joining process allows multiple alignments by remelting the solder. The alignment is done in the liquid phase of the solder by a 6 axis manipulator with a step width in the nm range and a tilt in the arc second range. In a next step the optical components have to pass the environmental tests. The total misalignment of the component to its adapter after the thermal cycle tests is less than 10 arc seconds. The mechanical stability tests regarding shear, vibration and shock behavior are well within the requirements
ΠΠ΅ΠΊΠΎΡΠΎΡΡΠ΅ ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΡ ΠΏΡΠΈΠΌΠ΅Π½Π΅Π½ΠΈΡ ΠΌΠ΅ΡΠΎΠ΄Π° Π³Π΅ΠΎΠΌΠ΅ΡΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ Π°Π½Π°Π»ΠΈΠ·Π° Π΄ΠΈΠ·ΡΡΠ½ΠΊΡΠΎΠ² Π΄Π»Ρ ΠΏΠΎΠΈΡΠΊΠΎΠ² ΡΠΌΠ΅ΡΠ΅Π½Π½ΠΎΠ³ΠΎ ΠΊΡΡΠ»Π° ΠΏΠ»Π°ΡΡΠ° Π² ΠΡΠΎΠΊΠΎΠΏΡΠ΅Π²ΡΠΊΠΎΠΌ ΡΠ°ΠΉΠΎΠ½Π΅ ΠΡΠ·Π±Π°ΡΡΠ°
In this paper we present the development of a compact, thermo-optically stable and vibration and mechanical shock resistant mounting technique by soldering of optical components. Based on this technique, new generations of laser pump sources for aerospace applications are designed. In these laser systems the used soldering technique replaces the glued connection between the optical component and its join partner. The main challenges are the alignment accuracy in the arc second range and the realization of the long term stability of every single part in the laser system (e.g. resonator mirrors)
Theory of spin-2 Bose-Einstein condensates: spin-correlations, magnetic response, and excitation spectra
The ground states of Bose-Einstein condensates of spin-2 bosons are
classified into three distinct (ferromagnetic, ^^ ^^ antiferromagnetic", and
cyclic) phases depending on the s-wave scattering lengths of binary collisions
for total-spin 0, 2, and 4 channels. Many-body spin correlations and magnetic
response of the condensate in each of these phases are studied in a mesoscopic
regime, while low-lying excitation spectra are investigated in the hermodynamic
regime. In the mesoscopic regime, where the system is so tightly confined that
the spatial degrees of freedom are frozen, the exact, many-body ground state
for each phase is found to be expressed in terms of the creation operators of
pair or trio bosons having spin correlations. These pairwise and trio-wise
units are shown to bring about some unique features of spin-2 BECs such as a
huge jump in magnetization from minimum to maximum possible values and the
robustness of the minimum-magnetization state against an applied agnetic field.
In the thermodynamic regime, where the system is spatially uniform, low-lying
excitation spectra in the presence of magnetic field are obtained analytically
using the Bogoliubov approximation. In the ferromagnetic phase, the excitation
spectrum consists of one Goldstone mode and four single-particle modes. In the
antiferromagnetic phase, where spin-singlet ^^ ^^ pairs" undergo Bose-Einstein
condensation, the spectrum consists of two Goldstone modes and three massive
ones, all of which become massless when magnetic field vanishes. In the cyclic
phase, where boson ^^ ^^ trios" condense into a spin-singlet state, the
spectrum is characterized by two Goldstone modes, one single-particle mode
having a magnetic-field-independent energy gap, and a gapless single-particle
mode that becomes massless in the absence of magnetic field.Comment: 28 pages, 4 figure
The Expedition to the Peel River in 2019: Fluvial Transport Across a Permafrost Landscape
The Expedition to the Peel River in 2019: Fluvial Transport Across a Permafrost Landscape EU Horizon2020 project, Nunataryuk. Consisting of 7 legs from 16 June 2019 - 11 August 2019
Polariton Bose-Einstein condensate at room temperature in a Al(Ga)N nanowire-dielectric microcavity with a spatial potential trap
A spatial potential trap is formed in a 6.0 {\mu}m Al(Ga)N nanowire by
varying the Al composition along its length during epitaxial growth. The
polariton emission characteristics of a dielectric microcavity with the single
nanowire embedded in-plane has been studied at room temperature. Excitation is
provided at the Al(Ga)N end of the nanowire and polariton emission is observed
from the lowest bandgap GaN region of the nanowire. Comparison of the results
with those measured in an identical microcavity with an uniform GaN nanowire
and having an identical exciton-photon detuning suggests evaporative cooling of
the polaritons as they are transported across the trap in the Al(Ga)N nanowire.
Measurement of the spectral characteristics of the polariton emission, their
momentum distribution, first-order spatial coherence and time-resolved
measurements of polariton cooling provide strong evidence of the formation of
an equilibrium Bose-Einstein condensate, a unique state of matter in solid
state systems, in the GaN region of the nanowire, at room temperature. An
equilibrium condensate is not formed in the GaN nanowire dielectric microcavity
without the spatial potential trap.Comment: 28 pages, 6 figures, Submitted to the Proceedings of the National
Academy of Sciences of the United States of Americ
Quantum tunneling across spin domains in a Bose-Einstein condensate
Quantum tunneling was observed in the decay of metastable spin domains in
gaseous Bose-Einstein condensates. A mean-field description of the tunneling
was developed and compared with measurement. The tunneling rates are a
sensitive probe of the boundary between spin domains, and indicate a spin
structure in the boundary between spin domains which is prohibited in the bulk
fluid. These experiments were performed with optically trapped F=1 spinor
Bose-Einstein condensates of sodium.Comment: 5 pages, 4 figure
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