Weak measurements and the joint estimation of phase and phase diffusion

Weak measurements offer the possibility of tuning the information acquired on a system, hence the imposed disturbance. This suggests that it could be a useful tool for multiparameter estimation, when two parameters cannot be measured simultaneously at the quantum limit. Here we discuss their use for phase estimation in the presence of phase diffusion in the context of polarimetry, a scenario that is conveniently cast in terms of a two-level quantum system in many relevant cases

Tailoring Multiloop Atom Interferometers with Adjustable Momentum Transfer

International audienceMulti-loop matter-wave interferometers are essential in quantum sensing to extract physical quantities and their derivatives in time or space. They are realized by stacking several mirror stages, but the finite efficiency of the matter-wave mirrors creates spurious paths which scramble the signal of interest. Here we demonstrate a method of adjustable momentum transfer that prevents the recombination of the spurious paths in a double-loop cold-atom interferometer aimed at measuring rotation rates. We experimentally study the recombination condition of the spurious matter waves, which is quantitatively supported by a model accounting for the coherence properties of the atomic source. We finally demonstrate the effectiveness of the method in building a cold-atom gyroscope with zero residual acceleration sensitivity. Our study will impact the design of multi-loop atom interferometers that measure a unique inertial quantity. Matter-wave interference is a central concept of quantum mechanics with a myriad of applications making use of electrons [1], neutrons [2], or atoms and molecules [3]. Examples of applications range from bacteria characterization [4] and biomolecular analysis [5], to fundamental physics tests [6] and accurate inertial sensing [7]. In most cases, a required high degree of control over the interference conditions and the precision of a measurement rely on the interference of two waves, with a sinusoidal fringe pattern providing direct access to the phase shift. The presence of auxiliary interferometic loops due to the imperfection of the mirrors, may, on the contrary, result in a multiple-wave interference that scrambles the signal of interest even in the absence of the noise sources. Light-pulse atom interferometers employ a train of so-called atom optics elements-dedicated laser pulses that split, deflect and recombine the atomic waves making them follow spatially distinct trajectories enclosing in the simplest case a single loop, in a geometry similar to that of an optical Mach-Zehnder interferometer. Accessing spatial derivatives of physical quantities (e.g. gradients of magnetic or gravitational fields) or a selective measurement of one among several contributions often requires interferometers consisting of several loops [8, 9], realized by multiple deflection of the matter-waves with additional mirrors-a technique analogous to the multi-pulse magnetic resonance spectroscopy [10]. The finite transmission of the atomic mirrors leads to the appearance of spurious leaked matter waves, which, in presence of additional mirrors, become redirected and eventually form closed interferometric loops, degrading the two-wave nature of the interferometer [11]. Understanding and controlling the recombination of these spurious paths is intimately linked to the coherence of the matter-wave source, and requires a tailored design of the interferometric sequence and atomic mirrors. In this Letter, we report on a method which prevents the recombination of the spurious paths in multi-loop cold-atom interferometers, both in position and in momentum space. Our method uses atomic mirrors transferring an adjustable momentum to the atom. The high degree of control provided by this method, compared to other techniques in matter-wave interferometry, enables the detailed, though general, study of the process of the recombination of wave-packets. Finally, we show that the method of adjustable momentum transfer (AMT) allows for building a pure-rate gyroscope, as theoretically proposed in Ref. [12]. Our results can be generalized to atom-interferometric sensors of arbitrary multi-loop ar-chitectures. We implement the AMT method in a double-loop atom interferometer aimed at measuring rotation rates and described in Refs. [13, 14]. In short, we laser-cool Cesium atoms in a single internal state |F = 4 to the temperature of 1.8 µK, and launch them vertically using moving molasses in an atomic fountain. The atom optics employ stimulated Raman transitions at 852 nm that couple the |F = 3 and |F = 4 internal states with two counter-propagating laser fields of wave-vectors k 3 and k 4 , imparting a momentum k eff = (k 3 − k 4) to the diffracted part of the wave-packet [15]. The inter-ferometric sequence comprising four Raman laser pulses of π/2, π, π, π/2 Rabi angles, forms a symmetric double-loop path diagram of the split wave-packets, which will be discussed in detail later. The resulting accumulated phase difference is read out from the probability of transition between the two internal states using fluorescence detection and internal-state labeling of the output ports of the interferometer [16]. Two pairs of Raman beams access the interrogation region from two collimators as shown in Fig. 1(a). Each pair is retro-reflected by a mirror. The mirrors are parallel to each other to better than 0.2 µrad [17] and tilted by an angle θ 0 = 3.8 • with respect to the horizontal direc-tionx, in order to lift the degeneracy between the ± k eff transitions owing to the Doppler effect. The top collima-tor can be further inclined by a small adjustable angle arXiv:2006.08371v1 [physics.atom-ph

Interleaved Atom Interferometry for High Sensitivity Inertial Measurements

Cold-atom inertial sensors target several applications in navigation, geoscience and tests of fundamental physics. Reaching high sampling rates and high inertial sensitivities, obtained with long interrogation times, represents a challenge for these applications. We report on the interleaved operation of a cold-atom gyroscope, where 3 atomic clouds are interrogated simultaneously in an atom interferometer featuring a 3.75 Hz sampling rate and an interrogation time of 801 ms. Interleaving improves the inertial sensitivity by efficiently averaging vibration noise, and allows us to perform dynamic rotation measurements in a so-far unexplored range. We demonstrate a stability of $3\times 10^{-10}$ rad.s$^{-1}$, which competes with the best stability levels obtained with fiber-optics gyroscopes. Our work validates interleaving as a key concept for future atom-interferometry sensors probing time-varying signals, as in on-board navigation and gravity-gradiometry, searches for dark matter, or gravitational wave detection

Accurate trajectory alignment in cold-atom interferometers with separated laser beams

International audienceCold-atom interferometers commonly face systematic effects originating from the coupling between the trajectory of the atomic wave packet and the wavefront of the laser beams driving the interferometer. Detrimental for the accuracy and the stability of such inertial sensors, these systematics are particularly enhanced in architectures based on spatially separated laser beams. Here we analyze the effect of a coupling between the relative alignment of two separated laser beams and the trajectory of the atomic wave packet in a four-light-pulse cold-atom gyroscope operated in fountain configuration. We present a method to align the two laser beams at the 0.2μrad level and to determine the optimal mean velocity of the atomic wave packet with an accuracy of 0.2mms−1. Such fine tuning constrains the associated gyroscope bias to a level of 1×10−10rads−1. In addition, we reveal this coupling using the point-source interferometry technique by analyzing single-shot time-of-flight fluorescence traces, which allows us to measure large angular misalignments between the interrogation beams. The alignment method which we present here can be employed in other sensor configurations and is particularly relevant to emerging gravitational wave detector concepts based on cold-atom interferometry

Atom Interferometry with Top-Hat Laser Beams

International audienceThe uniformity of the intensity and the phase of laser beams is crucial to high-performance atom interferometers. Inhomogeneities in the laser intensity profile cause contrast reductions and systematic effects in interferometers operated with atom sources at micro-Kelvin temperatures and detrimental diffraction phase shifts in interferometers using large momentum transfer beam splitters. We report on the implementation of a so-called top-hat laser beam in a long-interrogation-time cold-atom interferometer to overcome the issue of inhomogeneous laser intensity encountered when using Gaussian laser beams. We characterize the intensity and relative phase profiles of the top-hat beam and demonstrate its gain in atom-optic efficiency over a Gaussian beam, in agreement with numerical simulations. We discuss the application of top-hat beams to improve the performance of different architectures of atom interferometers

Bariatric reduction system–BARS: device, technique and first clinical experience

Background: Roux-en-Y gastric by-pass (RYGB) is one of the most effective bariatric procedures, but the rate of weight regain (WR) can reach 63% after the second year. Enlargement of the gastrojejunal anastomosis is one of the reported causes. A newly CE-marked flexible endoscopic system, Bariatric Anastomotic Reduction System (BARS) (Ovesco Endoscopy, Tuebingen, Germany), derivative of the well-established endoscopic over-the-scope-clip (OTSC) clipping system, has been recently developed. It was tested in pre-clinical and preliminary clinical use for feasibility and effectiveness in bariatric anastomotic reduction. Material and methods: Using a single-channel endoscope with external supplemental working channel, the BARS device captures the two limbs of the anastomosis, reducing its size, thus slowing food passage. After preclinical assessment, six patients with at least a 15% WR and the presence of an enlarged gastrojejunostomy > 20 mm were enrolled. The mean patient age was 49 years (range 24-67). Average interval between gastric bypass and BARS procedure: 8 years (4-13). Results: All procedures were safely performed without complications. Mean procedure time: 52 min (37 - 75). Preliminary results: mean weight loss 6 kg (4-9) at a 3-month FU. Conclusions: BARS could be a promising endoscopic system in case of WR after gastric bypass due to enlargement of the anastomosis

SICOB-endorsed national Delphi consensus on obesity treatment optimization: focus on diagnosis, pre-operative management, and weight regain/insufficient weight loss approach

Purpose: Overweight and obesity affects 60% of adults causing more than 1.2 million deaths across world every year. Fight against involved different specialist figures and multiple are the approved weapons. Aim of the present survey endorsed by the Italian Society of Bariatric Surgery (SICOB) is to reach a national consensus on obesity treatment optimization through a Delphi process. Methods: Eleven key opinion leaders (KOLs) identified 22 statements with a major need of clarification and debate. The explored pathways were: (1) Management of patient candidate to bariatric/metabolic surgery (BMS); (2) Management of patient not eligible for BMS; (3) Management of patient with short-term (2 years) weight regain (WR) or insufficient weight loss (IWL); (4) Management of the patient with medium-term (5 years) WR; and (5) Association between drugs and BMS as WR prevention. The questionnaire was distributed to 65 national experts via an online platform with anonymized results. Results: 54 out of 65 invited panelists (83%) respond. Positive consensus was reached for 18/22 statements (82%); while, negative consensus (s20.4; s21.5) and no consensus (s11.5, s17) were reached for 2 statements, respectively (9%). Conclusion: The Delphi results underline the importance of first-line interdisciplinary management, with large pre-treatment examination, and establish a common opinion on how to properly manage post-operative IWL/WR. Level of evidence V: Report of expert committees