253 research outputs found
Bosenova and three-body loss in a Rb-85 Bose-Einstein condensate
Collapsing Bose-Einstein condensates are rich and complex quantum systems for
which quantitative explanation by simple models has proved elusive. We present
new experimental data on the collapse of high density Rb-85 condensates with
attractive interactions and find quantitative agreement with the predictions of
the Gross-Pitaevskii equation. The collapse data and measurements of the decay
of atoms from our condensates allow us to put new limits on the value of the
Rb-85 three-body loss coefficient K_3 at small positive and negative scattering
lengths.Comment: 6 pages, 5 figure
Cold atom gravimetry with a Bose-Einstein Condensate
We present a cold atom gravimeter operating with a sample of Bose-condensed
Rubidium-87 atoms. Using a Mach-Zehnder configuration with the two arms
separated by a two-photon Bragg transition, we observe interference fringes
with a visibility of 83% at T=3 ms. We exploit large momentum transfer (LMT)
beam splitting to increase the enclosed space-time area of the interferometer
using higher-order Bragg transitions and Bloch oscillations. We also compare
fringes from condensed and thermal sources, and observe a reduced visibility of
58% for the thermal source. We suspect the loss in visibility is caused partly
by wavefront aberrations, to which the thermal source is more susceptible due
to its larger transverse momentum spread. Finally, we discuss briefly the
potential advantages of using a coherent atomic source for LMT, and present a
simple mean-field model to demonstrate that with currently available
experimental parameters, interaction-induced dephasing will not limit the
sensitivity of inertial measurements using freely-falling, coherent atomic
sources.Comment: 6 pages, 4 figures. Final version, published PR
Quantum projection noise limited interferometry with coherent atoms in a Ramsey type setup
Every measurement of the population in an uncorrelated ensemble of two-level
systems is limited by what is known as the quantum projection noise limit.
Here, we present quantum projection noise limited performance of a Ramsey type
interferometer using freely propagating coherent atoms. The experimental setup
is based on an electro-optic modulator in an inherently stable Sagnac
interferometer, optically coupling the two interfering atomic states via a
two-photon Raman transition. Going beyond the quantum projection noise limit
requires the use of reduced quantum uncertainty (squeezed) states. The
experiment described demonstrates atom interferometry at the fundamental noise
level and allows the observation of possible squeezing effects in an atom
laser, potentially leading to improved sensitivity in atom interferometers.Comment: 8 pages, 8 figures, published in Phys. Rev.
11 W narrow linewidth laser source at 780nm for laser cooling and manipulation of Rubidium
We present a narrow linewidth continuous laser source with over 11 Watts of
output power at 780nm, based on single-pass frequency doubling of an amplified
1560nm fibre laser with 36% efficiency. This source offers a combination of
high power, simplicity, mode quality and stability. Without any active
stabilization, the linewidth is measured to be below 10kHz. The fibre seed is
tunable over 60GHz, which allows access to the D2 transitions in 87Rb and 85Rb,
providing a viable high-power source for laser cooling as well as for
large-momentum-transfer beamsplitters in atom interferometry. Sources of this
type will pave the way for a new generation of high flux, high duty-cycle
degenerate quantum gas experiments.Comment: 5 pages, 3 figure
Optically trapped atom interferometry using the clock transition of large Rb-87 Bose-Einstein condensates
We present a Ramsey-type atom interferometer operating with an optically
trapped sample of 10^6 Bose-condensed Rb-87 atoms. The optical trap allows us
to couple the |F =1, mF =0>\rightarrow |F =2, mF =0> clock states using a
single photon 6.8GHz microwave transition, while state selective readout is
achieved with absorption imaging. Interference fringes with contrast
approaching 100% are observed for short evolution times. We analyse the process
of absorption imaging and show that it is possible to observe atom number
variance directly, with a signal-to-noise ratio ten times better than the
atomic projection noise limit on 10^6 condensate atoms. We discuss the
technical and fundamental noise sources that limit our current system, and
outline the improvements that can be made. Our results indicate that, with
further experimental refinements, it will be possible to produce and measure
the output of a sub-shot-noise limited, large atom number BEC-based
interferometer.
In an addendum to the original paper, we attribute our inability to observe
quantum projection noise to the stability of our microwave oscillator and
background magnetic field. Numerical simulations of the Gross-Pitaevskii
equations for our system show that dephasing due to spatial dynamics driven by
interparticle interactions account for much of the observed decay in fringe
visibility at long interrogation times. The simulations show good agreement
with the experimental data when additional technical decoherence is accounted
for, and suggest that the clock states are indeed immiscible. With smaller
samples of 5 \times 10^4 atoms, we observe a coherence time of {\tau} =
(1.0+0.5-0.3) s.Comment: 22 pages, 6 figures Addendum: 11 pages, 6 figure
Optically guided linear Mach Zehnder atom interferometer
We demonstrate a horizontal, linearly guided Mach Zehnder atom interferometer
in an optical waveguide. Intended as a proof-of-principle experiment, the
interferometer utilises a Bose-Einstein condensate in the magnetically
insensitive |F=1,mF=0> state of Rubidium-87 as an acceleration sensitive test
mass. We achieve a modest sensitivity to acceleration of da = 7x10^-4 m/s^2.
Our fringe visibility is as high as 38% in this optically guided atom
interferometer. We observe a time-of-flight in the waveguide of over half a
second, demonstrating the utility of our optical guide for future sensors.Comment: 6 pages, 3 figures. Submitted to Phys. Rev.
Advice after urgent suspected cancer referral when cancer is not found in England: Survey of patients’ preferences and perceived acceptability
Objective
No standardised approach exists to provide advice after urgent suspected cancer (USC) referral when cancer is not found. This study aimed to assess preferences and acceptability of receiving advice after USC referral related to: 1) managing ongoing symptoms, 2) responding to early symptoms of other cancers, 3) cancer screening, 4) reducing risks of future cancer.
Methods
2,541 patients from two English NHS Trusts were mailed a survey 1–3 months after having no cancer found following urgent suspected gastrointestinal or head and neck cancer referral. Participants were asked about: willingness to receive advice; prospective acceptability; preferences related to mode, timing and who should provide advice; and previous advice receipt.
Results
406 patients responded (16.0%) with 397 in the final analyses. Few participants had previously received advice, yet most were willing to. Willingness varied by type of advice: fewer were willing to receive advice about early symptoms of other cancers (88.9%) than advice related to ongoing symptoms (94.3%). Acceptability was relatively high for all advice types. Reducing the risk of future cancer advice was more acceptable. Acceptability was lower in those from ethnic minority groups, and with lower levels of education. Most participants preferred to receive advice from a doctor; with results or soon after; either face to face or via the telephone.
Conclusions
There is a potential unmet need for advice after USC referral when no cancer is found. Equitable intervention design should focus on increasing acceptability for people from ethnic minority groups and those with lower levels of education
Precision atomic gravimeter based on Bragg diffraction
We present a precision gravimeter based on coherent Bragg diffraction of
freely falling cold atoms. Traditionally, atomic gravimeters have used
stimulated Raman transitions to separate clouds in momentum space by driving
transitions between two internal atomic states. Bragg interferometers utilize
only a single internal state, and can therefore be less susceptible to
environmental perturbations. Here we show that atoms extracted from a
magneto-optical trap using an accelerating optical lattice are a suitable
source for a Bragg atom interferometer, allowing efficient beamsplitting and
subsequent separation of momentum states for detection. Despite the inherently
multi-state nature of atom diffraction, we are able to build a Mach-Zehnder
interferometer using Bragg scattering which achieves a sensitivity to the
gravitational acceleration of with an
integration time of 1000s. The device can also be converted to a gravity
gradiometer by a simple modification of the light pulse sequence.Comment: 13 pages, 11 figure
- …