72 research outputs found
Atom-wave diffraction between the Raman-Nath and the Bragg regime: Effective Rabi frequency, losses, and phase shifts
We present an analytic theory of the diffraction of (matter) waves by a
lattice in the "quasi-Bragg" regime, by which we mean the transition region
between the long-interaction Bragg and "channelling" regimes and the
short-interaction Raman-Nath regime. The Schroedinger equation is solved by
adiabatic expansion, using the conventional adiabatic approximation as a
starting point, and re-inserting the result into the Schroedinger equation to
yield a second order correction. Closed expressions for arbitrary pulse shapes
and diffraction orders are obtained and the losses of the population to output
states otherwise forbidden by the Bragg condition are derived. We consider the
phase shift due to couplings of the desired output to these states that depends
on the interaction strength and duration and show how these can be kept
negligible by a choice of smooth (e.g., Gaussian) envelope functions even in
situations that substantially violate the adiabaticity condition. We also give
an efficient method for calculating the effective Rabi frequency (which is
related to the eigenvalues of Mathieu functions) in the quasi-Bragg regime.Comment: Minor additions, more concise text. To appear in Phys. Rev. A. 20
pages, 10 figure
Atom interferometers with scalable enclosed area
Bloch oscillations (i.e., coherent acceleration of matter waves by an optical
lattice) and Bragg diffraction are integrated into light-pulse atom
interferometers with large momentum splitting between the interferometer arms,
and hence enhanced sensitivity. Simultaneous acceleration of both arms in the
same internal states suppresses systematic effects, and simultaneously running
a pair of interferometers suppresses the effect of vibrations. Ramsey-Bord\'e
interferometers using four such Bloch-Bragg-Bloch (BBB) beam splitters exhibit
15% contrast at 24 splitting, the largest so far ( is the
photon momentum); single beam splitters achieve 88. The prospects for
reaching 100s of and applications like gravitational wave sensors are
discussed.Comment: 4 pages, 5 figure
A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer
We built an ultra low noise angle sensor by combining a folded optical lever
and a Sagnac interferometer. The instrument has a measured noise floor of 1.3
prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a
proof-of-concept apparatus with a conservative N=11 bounces in the optical
lever. This technique could be extended to reach sub-picoradian / Hz^(1/2)
sensitivities with an optimized design.Comment: 3 pages, 4 figure
Broadband Optical Serrodyne Frequency Shifting
We demonstrate serrodyne frequency shifting of light from 200 MHz to 1.2 GHz
with an efficiency of better than 60 percent. The frequency shift is imparted
by an electro-optic phase modulator driven by a high-frequency, high-fidelity
sawtooth waveform that is passively generated by a commercially available
Non-Linear Transmission Line (NLTL). We also implement a push-pull
configuration using two serrodyne-driven phase modulators allowing for
continuous tuning between -1.6 GHz and +1.6 GHz. Compared to competing
technologies, this technique is simple and robust, and offers the largest
available tuning range in this frequency band.Comment: 3 pages, 4 figure
Safety and feasibility of robotic-assisted drainage of symptomatic pancreatic pseudocysts: A case-series analysis (with video)
The surgical treatment of pancreatic pseudocysts (PPs) in patients who fail nonoperative management has evolved from aggressive open to a minimally invasive approach. The application of robotic surgery in this setting is scarcely reported. The aim of this study is to analyze the safety and feasibility of the robotic approach to pancreatic pseudocyst drainage. A single centre retrospective review of consecutive patients undergoing robotic-assisted pancreatic pseudocyst surgeries in an academic tertiary institution was performed. There were 14 patients studied, of whom 10 underwent cystogastrostomy and 4 Roux-En-Y cystojejunostomy. Eight patients had gallstone pancreatitis and 3 patients alcoholic pancreatitis. The mean size of cyst was 8.9±1cm and 57.1% located at the pancreatic body. The overall operative time of the procedure was 135±34 minutes. There were no open conversions. The overall success rate was 92.8%, while the primary success rate 85.7%. The major morbidity rate was 14.3% and there was no 30-day mortality. The mean post-operative hospital stay was 7±3 days with one recurrence of the pancreatic pseudocyst on follow-up requiring endoscopic drainage without further recurrence. The robotic approach for the drainage of symptomatic pancreatic pseudocyst is safe and feasible and can be considered as a viable modality for operative intervention in well-selected patient
An Atomic Gravitational Wave Interferometric Sensor in Low Earth Orbit (AGIS-LEO)
We propose an atom interferometer gravitational wave detector in low Earth
orbit (AGIS-LEO). Gravitational waves can be observed by comparing a pair of
atom interferometers separated over a ~30 km baseline. In the proposed
configuration, one or three of these interferometer pairs are simultaneously
operated through the use of two or three satellites in formation flight. The
three satellite configuration allows for the increased suppression of multiple
noise sources and for the detection of stochastic gravitational wave signals.
The mission will offer a strain sensitivity of < 10^(-18) / Hz^(1/2) in the 50
mHz - 10 Hz frequency range, providing access to a rich scientific region with
substantial discovery potential. This band is not currently addressed with the
LIGO or LISA instruments. We analyze systematic backgrounds that are relevant
to the mission and discuss how they can be mitigated at the required levels.
Some of these effects do not appear to have been considered previously in the
context of atom interferometry, and we therefore expect that our analysis will
be broadly relevant to atom interferometric precision measurements. Finally, we
present a brief conceptual overview of shorter-baseline (< 100 m) atom
interferometer configurations that could be deployed as proof-of-principle
instruments on the International Space Station (AGIS-ISS) or an independent
satellite.Comment: 37 pages, 21 figure
A new photon recoil experiment: towards a determination of the fine structure constant
We report on progress towards a measurement of the fine structure constant to
an accuracy of or better by measuring the ratio of the
Planck constant to the mass of the cesium atom. Compared to similar
experiments, ours is improved in three significant ways: (i) simultaneous
conjugate interferometers, (ii) multi-photon Bragg diffraction between same
internal states, and (iii) an about 1000 fold reduction of laser phase noise to
-138 dBc/Hz. Combining that with a new method to simultaneously stabilize the
phases of four frequencies, we achieve 0.2 mrad effective phase noise at the
location of the atoms. In addition, we use active stabilization to suppress
systematic effects due to beam misalignment.Comment: 12 pages, 9 figure
Exploring the limits of ultracold atoms in space
Existing space-based cold atom experiments have demonstrated the utility of microgravity for improvements in observation times and for minimizing the expansion energy and rate of a freely evolving coherent matter wave. In this paper we explore the potential for space-based experiments to extend the limits of ultracold atoms utilizing not just microgravity, but also other aspects of the space environment such as exceptionally good vacuums and extremely cold temperatures. The tantalizing possibility that such experiments may one day be able to probe physics of quantum objects with masses approaching the Planck mass is discussed
The Bose-Einstein Condensate and Cold Atom Laboratory
© 2020, The Author(s). Microgravity eases several constraints limiting experiments with ultracold and condensed atoms on ground. It enables extended times of flight without suspension and eliminates the gravitational sag for trapped atoms. These advantages motivated numerous initiatives to adapt and operate experimental setups on microgravity platforms. We describe the design of the payload, motivations for design choices, and capabilities of the Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL), a NASA-DLR collaboration. BECCAL builds on the heritage of previous devices operated in microgravity, features rubidium and potassium, multiple options for magnetic and optical trapping, different methods for coherent manipulation, and will offer new perspectives for experiments on quantum optics, atom optics, and atom interferometry in the unique microgravity environment on board the International Space Station
Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)
Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic
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