Rb-85 tunable-interaction Bose-Einstein condensate machine

We describe our experimental setup for creating stable Bose-Einstein condensates of Rb-85 with tunable interparticle interactions. We use sympathetic cooling with Rb-87 in two stages, initially in a tight Ioffe-Pritchard magnetic trap and subsequently in a weak, large-volume crossed optical dipole trap, using the 155 G Feshbach resonance to manipulate the elastic and inelastic scattering properties of the Rb-85 atoms. Typical Rb-85 condensates contain 4 x 10^4 atoms with a scattering length of a=+200a_0. Our minimalist apparatus is well-suited to experiments on dual-species and spinor Rb condensates, and has several simplifications over the Rb-85 BEC machine at JILA (Papp, 2007; Papp and Wieman, 2006), which we discuss at the end of this article.Comment: 10 pages, 8 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

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

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

Liposomes modulate human immunodeficiency virus infectivity

We have investigated the effects of the fusion of liposomes with human immunodeficiency virus type 1 (HIV-1(LVA)) on the ability of the virus to infect CD4+ and CD4- cells. Fluorescence dequenching measurements indicated that HIV-1 fuses with liposomes composed of either cardiolipin (CL) or N-[2,3-(dioleyloxy) propyl]-N,N,N-trimethyl ammonium chloride (DOTMA) but not appreciably with dioleoylphosphatidylcholine (DOPC) liposomes. Pre-incubation of HIV-1 with DOTMA liposomes enhanced virus production (measured by p24 gag antigen production in the culture medium and in situ) in CD4+ A3.01 and H9 cells in a concentration-dependent manner, but did not mediate the infection of the CD4- cell line, K562. Preincubation of HIV-1 with between 10 and 30 μM-DOTMA liposomes, and subsequent incubation with A3.01 cells, resulted in the production of about 30-fold greater levels of virus than controls. The presence of DOTMA liposomes during the incubation of A3.01 cells with HIV-1 enhanced the infectivity of the virus up to 90-fold compared to controls. Conversely, preincubation of HIV-1 with CL liposomes inhibited infection of A3.01 cells, dependent on the concentration of liposomes; DOPC liposomes did not alter the infectivity of the virus under any of the incubation conditions. Our results thus indicate that fusion of HIV-1 with liposomes alters the ability of the virus to infect its target cells

Simple piezoelectric-actuated mirror with 180 kHz servo bandwidth

We present a high bandwidth piezoelectric-actuated mirror for length stabilization of an optical cavity. The actuator displays a transfer function with a flat amplitude response and greater than 135$^\circ$ phase margin up to 200 kHz, allowing a 180 kHz unity gain frequency to be achieved in a closed servo loop. To the best of our knowledge, this actuator has achieved the largest servo bandwidth for a piezoelectric transducer (PZT). The actuator should be very useful in a wide variety of applications requiring precision control of optical lengths, including laser frequency stabilization, optical interferometers, and optical communications

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

Measurement of inelastic losses in a sample of ultracold Rb-85

We report on the observation and characterisation of an inelastic loss feature in collisions between ultracold Rb-85 |F=2, m_F=-2> atoms at a magnetic field of 220 G. Our apparatus creates ultracold Rb-85 clouds by sympathetic cooling with a Rb-87 reservoir, and can produce pure Rb-87 condensates of 10^6 atoms by a combination of evaporative cooling in a quadrupole-Ioffe magnetic trap and further evaporation in a weak, large-volume optical dipole trap. By combining Rb-85 and Rb-87 atoms collected in a dual-species magneto-optical trap and selectively evaporating the heavier isotope, we demonstrate strong sympathetic cooling of the Rb-85 cloud, increasing its phase space density by three orders of magnitude with no detectable loss in number. We have used ultracold samples created in this way to observe the variation of inelastic loss in ultracold Rb-85 as a function of magnetic field near the 155 G Feshbach resonance. We have also measured a previously unobserved loss feature at 219.9(1) G with a width of 0.28(6) G, which we associate with a narrow Feshbach resonance predicted by theory.Comment: 4 pages, 3 figures, content change

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 $\Delta g/g = 2.7\times10^{-9}$ 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

Linear-Accelerator Program

Contains reports on one research project