Damping and decoherence of Fock states in a nanomechanical resonator due to two level systems

We numerically investigate the decay of initial quantum Fock states and their superpositions for a mechanical resonator mode coupled to an environment comprising interacting, damped tunneling two level system (TLS) defects. The cases of one, three, and six near resonant, interacting TLS's are considered in turn and it is found that the resonator displays Ohmic bath like decay behavior with as few as three TLS's.Comment: 28 pages, 24 figures; submitted to Physical Review

Mesoscopic Mechanical Resonators as Quantum Non-Inertial Reference Frames

An atom attached to a micrometer-scale wire that is vibrating at a frequency of 100 MHz and with displacement amplitude 1 nm experiences an acceleration magnitude 10^9 ms^-2, approaching the surface gravity of a neutron star. As one application of such extreme non-inertial forces in a mesoscopic setting, we consider a model two-path atom interferometer with one path consisting of the 100 MHz vibrating wire atom guide. The vibrating wire guide serves as a non-inertial reference frame and induces an in principle measurable phase shift in the wave function of an atom traversing the wire frame. We furthermore consider the effect on the two-path atom wave interference when the vibrating wire is modeled as a quantum object, hence functioning as a quantum non-inertial reference frame. We outline a possible realization of the vibrating wire, atom interferometer using a superfluid helium quantum interference setup.Comment: Published versio

Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box

We analyse the quantum dynamics of a micromechanical resonator capacitively coupled to a Cooper box. With appropriate quantum state control of the Cooper box, the resonator can be driven into a superposition of spatially separated states. The Cooper box can also be used to probe the environmentally-induced decoherence of the resonator superposition state.Comment: 4 pages, 3 figure

Assessing the quality of written information provision for surgical procedures:A case study in oesophagectomy

OBJECTIVE: To examine the content and quality of written information provided by surgical centres for patients undergoing oesophagectomy for cancer. DESIGN: Cross-sectional study of the content of National Health Service (NHS) patient information leaflets (PILs) about oesophageal cancer surgery, using a modified framework approach. DATA SOURCES: Written information leaflets from 41 of 43 cancer centres undertaking surgery for oesophageal cancer in England and Wales (response rate 95.3%). ELIGIBILITY CRITERIA: All English language versions of PILs about oesophagectomy. RESULTS: 32 different PILs were identified, of which 2 were generic tools (Macmillan ‘understanding cancer of the gullet’ and EIDO ‘oesophagectomy’). Although most PILs focused on describing in-hospital adverse events, information varied widely and was often misleading. Just 1 leaflet described survival benefits of surgery and 2 mentioned the possibility of disease recurrence. CONCLUSIONS: Written information provided for patients by NHS cancer centres undertaking oesophagectomy is inconsistent and incomplete. It is recommended that surgeons work together with patients to agree on standards of information provision of relevance to all stakeholders’ needs

Measurement induced quantum-classical transition

A model of an electrical point contact coupled to a mechanical system (oscillator) is studied to simulate the dephasing effect of measurement on a quantum system. The problem is solved at zero temperature under conditions of strong non-equilibrium in the measurement apparatus. For linear coupling between the oscillator and tunneling electrons, it is found that the oscillator dynamics becomes damped, with the effective temperature determined by the voltage drop across the junction. It is demonstrated that both the quantum heating and the quantum damping of the oscillator manifest themselves in the current-voltage characteristic of the point contact.Comment: in RevTex, 1 figure, corrected notatio

Nonlinear response of a driven vibrating nanobeam in the quantum regime

We analytically investigate the nonlinear response of a damped doubly clamped nanomechanical beam under static longitudinal compression which is excited to transverse vibrations. Starting from a continuous elasticity model for the beam, we consider the dynamics of the beam close to the Euler buckling instability. There, the fundamental transverse mode dominates and a quantum mechanical time-dependent effective single particle Hamiltonian for its amplitude can be derived. In addition, we include the influence of a dissipative Ohmic or super-Ohmic environment. In the rotating frame, a Markovian master equation is derived which includes also the effect of the time-dependent driving in a non-trivial way. The quasienergies of the pure system show multiple avoided level crossings corresponding to multiphonon transitions in the resonator. Around the resonances, the master equation is solved analytically using Van Vleck perturbation theory. Their lineshapes are calculated resulting in simple expressions. We find the general solution for the multiple multiphonon resonances and, most interestingly, a bath-induced transition from a resonant to an antiresonant behavior of the nonlinear response.Comment: 25 pages, 5 figures, submitted to NJ

Pregnancy outcomes following different types of bariatric surgery: A national cohort study

OBJECTIVE: To assess the impact of type of bariatric surgery on pregnancy outcomes. STUDY DESIGN: This is a national prospective observational study using the UK Obstetric Surveillance System (UKOSS). Data collection was undertaken in 200 consultant-led NHS maternity units between November 2011 and October 2012 (gastric banding), and April 2014 and March 2016 (gastric bypass and sleeve gastrectomy). Participants were pregnant women following gastric banding (n = 127), gastric bypass (n = 134) and sleeve gastrectomy (n = 29). Maternal and perinatal outcomes were compared using generalised linear and linear mixed models. Maternal outcomes included gestational weight gain, pre-eclampsia, gestational diabetes, anaemia, surgical complications. Perinatal outcomes included birthweight, small/large for gestational age (SGA/LGA), preterm birth, stillbirth. RESULTS: Maternal: Women pregnant after gastric banding and sleeve gastrectomy had a lower risk of anaemia compared with gastric bypass (banding (16 %) vs bypass (39 %): p = 0.002, sleeve (21 %) vs bypass: p = 0.04). Gestational diabetes risk was lower after gastric banding compared with gastric bypass (7 % vs 16 %, p = 0.03) despite women with banding having significantly greater weight at booking as well as gestational weight gain. Women pregnant after gastric banding and sleeve gastrectomy had a lower risk of surgical complications than after gastric bypass (banding (0.9 %) vs bypass (11.4 %): p = 0.03, sleeve (0.0 %) vs bypass: p = 0.06). Perinatal: Infants born to mothers after gastric banding had a higher birthweight than those born to mothers after gastric bypass (mean difference = 260 g (125-395), p < 0.001). Infants were more likely to be LGA if their mothers had gastric banding compared with gastric bypass or sleeve gastrectomy (banding (21 %) vs bypass (5 %): p = 0.006; banding vs sleeve (3 %): p = 0.03). Risk of preterm birth was higher in women with gastric banding compared with gastric bypass (13 % vs 8 %, p = 0.04). CONCLUSIONS: Women planning bariatric surgery should be counselled regarding the differing impacts of different types of procedure on any future pregnancy. Pre-existing gastric bypass is associated with higher rates of potentially serious surgical complications during pregnancy