1,962 research outputs found
Multiphoton transitions in a macroscopic quantum two-state system
We have observed multiphoton transitions between two macroscopic
quantum-mechanical superposition states formed by two opposite circulating
currents in a superconducting loop with three Josephson junctions. Resonant
peaks and dips of up to three-photon transitions were observed in spectroscopic
measurements when the system was irradiated with a strong RF-photon field. The
widths of the multiphoton absorption dips are shown to scale with the Bessel
functions in agreement with theoretical predictions derived from the Bloch
equation or from a spin-boson model.Comment: 4 pages, 3 figure
Split Instability of a Vortex in an Attractive Bose-Einstein Condensate
An attractive Bose-Einstein condensate with a vortex splits into two pieces
via the quadrupole dynamical instability, which arises at a weaker strength of
interaction than the monopole and the dipole instabilities. The split pieces
subsequently unite to restore the original vortex or collapse.Comment: 4 pages, 4 figures, added figures and references, revised tex
Split-merge cycle, fragmented collapse, and vortex disintegration in rotating Bose-Einstein condensates with attractive interactions
The dynamical instabilities and ensuing dynamics of singly- and
doubly-quantized vortex states of Bose-Einstein condensates with attractive
interactions are investigated using full 3D numerical simulations of the
Gross-Pitaevskii equation. With increasing the strength of attractive
interactions, a series of dynamical instabilities such as quadrupole, dipole,
octupole, and monopole instabilities emerge. The most prominent instability
depends on the strength of interactions, the geometry of the trapping
potential, and deviations from the axisymmetry due to external perturbations.
Singly-quantized vortices split into two clusters and subsequently undergo
split-merge cycles in a pancake-shaped trap, whereas the split fragments
immediately collapse in a spherical trap. Doubly-quantized vortices are always
unstable to disintegration of the vortex core. If we suddenly change the
strength of interaction to within a certain range, the vortex splits into three
clusters, and one of the clusters collapses after a few split-merge cycles. The
vortex split can be observed using a current experimental setup of the MIT
group.Comment: 11 pages, 10 figure
Collapsing Bose-Einstein condensates beyond the Gross-Pitaevskii approximation
We analyse quantum field models of the bosenova experiment, in which
Rb Bose-Einstein condensates were made to collapse by switching their
atomic interactions from repulsive to attractive. Specifically, we couple the
lowest order quantum field correlation functions to the Gross-Pitaevskii
function, and solve the resulting dynamical system numerically. Comparing the
computed collapse times with the experimental measurements, we find that the
calculated times are much larger than the measured values. The addition of
quantum field corrections does not noticeably improve the agreement compared to
a pure Gross-Pitaevskii theory.Comment: 8 pages, 4 figure
Vacuum Rabi oscillations in a macroscopic superconducting qubit LC oscillator system
We have observed the coherent exchange of a single energy quantum between a
flux qubit and a superconducting LC circuit acting as a quantum harmonic
oscillator. The exchange of an energy quantum is known as the vacuum Rabi
oscillations: the qubit is oscillating between the excited state and the ground
state and the oscillator between the vacuum state and the first excited state.
We have also obtained evidence of level quantization of the LC circuit by
observing the change in the oscillation frequency when the LC circuit was not
initially in the vacuum state.Comment: Submitted to Phys. Rev. Let
d-wave collapse and explosion of a dipolar Bose-Einstein condensate
We investigate the collapse dynamics of a dipolar condensate of 52Cr atoms
when the s-wave scattering length characterizing the contact interaction is
reduced below a critical value. A complex dynamics, involving an anisotropic,
d-wave symmetric explosion of the condensate, is observed. The atom number
decreases abruptly during the collapse. We find good agreement between our
experimental results and those of a numerical simulation of the
three-dimensional Gross-Pitaevskii equation, including contact and dipolar
interactions as well as three-body losses. The simulation indicates that the
collapse induces the formation of two vortex rings with opposite circulations.Comment: 4 pages, 4 figure
Carbon K-shell photoelectron angular distribution from fixed-in-space CO2 molecules
Measurements of photoelectron angular distributions for carbon K-shell ionization of fixed-in-space CO2 molecules with the molecular axis oriented along, perpendicular and at 45 degrees to the electric vector of the light are reported. The major features of these measured spectra are fairly well reproduced by calculations employing a relaxed-core Hartree-Fock approach. In contrast to the angular distribution for K-shell ionization of N-2, which exhibits a rich structure dominated by the f-wave (l = 3) at the shape resonance, the angular distribution for carbon K-shell photoionization of CO2 is quite unstructured over the entire observed range across the shape resonance
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