902 research outputs found
Squeezing on momentum states for atom interferometry
We propose and analyse a method that allows for the production of squeezed
states of the atomic center-of-mass motion that can be injected into an atom
interferometer. Our scheme employs dispersive probing in a ring resonator on a
narrow transition of strontium atoms in order to provide a collective
measurement of the relative population of two momentum states. We show that
this method is applicable to a Bragg diffraction-based atom interferometer with
large diffraction orders. The applicability of this technique can be extended
also to small diffraction orders and large atom numbers by inducing atomic
transparency at the frequency of the probe field, reaching an interferometer
phase resolution scaling , where is the atom
number. We show that for realistic parameters it is possible to obtain a 20 dB
gain in interferometer phase estimation compared to the Standard Quantum Limit.Comment: 5 pages, 4 figure
Neural signature kernels as infinite-width-depth-limits of controlled ResNets
Motivated by the paradigm of reservoir computing, we consider randomly
initialized controlled ResNets defined as Euler-discretizations of neural
controlled differential equations (Neural CDEs). We show that in the
infinite-width-then-depth limit and under proper scaling, these architectures
converge weakly to Gaussian processes indexed on some spaces of continuous
paths and with kernels satisfying certain partial differential equations (PDEs)
varying according to the choice of activation function. In the special case
where the activation is the identity, we show that the equation reduces to a
linear PDE and the limiting kernel agrees with the signature kernel of Salvi et
al. (2021). In this setting, we also show that the width-depth limits commute.
We name this new family of limiting kernels neural signature kernels. Finally,
we show that in the infinite-depth regime, finite-width controlled ResNets
converge in distribution to Neural CDEs with random vector fields which,
depending on whether the weights are shared across layers, are either
time-independent and Gaussian or behave like a matrix-valued Brownian motion
Bragg gravity-gradiometer using the S-P intercombination transition of Sr
We present a gradiometer based on matter-wave interference of
alkaline-earth-metal atoms, namely Sr. The coherent manipulation of the
atomic external degrees of freedom is obtained by large-momentum-transfer Bragg
diffraction, driven by laser fields detuned away from the narrow
S-P intercombination transition. We use a well-controlled
artificial gradient, realized by changing the relative frequencies of the Bragg
pulses during the interferometer sequence, in order to characterize the
sensitivity of the gradiometer. The sensitivity reaches
s for an interferometer time of 20 ms, limited only by geometrical
constraints. We observed extremely low sensitivity of the gradiometric phase to
magnetic field gradients, approaching a value 10 times lower than the
sensitivity of alkali-atom based gradiometers. An efficient double-launch
technique employing accelerated red vertical lattices from a single
magneto-optical trap cloud is also demonstrated. These results highlight
strontium as an ideal candidate for precision measurements of gravity
gradients, with potential application in future precision tests of fundamental
physics.Comment: 10 pages, 7 figure
Canceling the cavity length induced phase noise in an optical ring cavity for phase shift measurement and spin squeezing
We demonstrate a new method of light phase shift measurement using a
high-finesse optical ring cavity which exhibits reduced phase noise due to
cavity length fluctuations. Two laser beams with a frequency difference of one
cavity free spectral range are simultaneously resonant with the cavity,
demonstrating noise correlations in the error signals due to the common-mode
cavity length fluctuations. The differential error signal shows a 30 dB
reduction in cavity noise down to the noise floor in a frequency range up to
half the cavity linewidth ( kHz). Various noise sources
are analyzed and their contributions to the noise floor are evaluated.
Additionally, we apply this noise-reduced phase shift measurement scheme in a
simulated spin-squeezing experiment where we have achieved a factor of 40
improvement in phase sensitivity with a phase resolution of 0.7 mrad, which may
remove one important barrier against attaining highly spin-squeezed states. The
demonstrated method is the first reported measurement using an optical ring
cavity and two independent beams, a flexible situation. This method can find
direct application to non-destructive measurements in quantum systems, such as
for the generation of spin-squeezed states in atom interferometers and atomic
clocks.Comment: 9 pages, 5 figure
Squeezed state metrology with Bragg interferometers operating in a cavity
Bragg interferometers, operating using pseudospin-1/2 systems composed of two momentum states, have become a mature technology for precision measurements. State-of-the-art Bragg interferometers are rapidly surpassing technical limitations and are soon expected to operate near the projection noise limit set by uncorrelated atoms. Despite the use of large numbers of atoms, their operation is governed by single-atom physics. Motivated by recent proposals and demonstrations of Raman gravimeters in cavities, we propose a scheme to squeeze directly on momentum states for surpassing the projection noise limit in Bragg interferometers. In our modeling, we consider the unique issues that arise when a spin squeezing protocol is applied to momentum pseudospins. Specifically, we study the effects of the momentum width of the atomic cloud and the coupling to momentum states outside the pseudospin manifold, as these atoms interact via a mode of the cavity.Weshow that appreciable levels of spin squeezing can be demonstrated in suitable parameter regimes in spite of these complications. Using this setting, we show how beyond mean-field techniques developed for spin systems can be adapted to study the dynamics of momentum states of interacting atoms. Our scheme promises to be feasible using current technology and is experimentally attractive because it requires no additional setup beyond what will be required to operate Bragg interferometers in cavities
Novel Adaptive Fixturing for Precise Micro-positioning of Thin Walled Parts
Fixtures are used to locate and hold workpieces during machining.
Because workpiece surface errors and fixture set-up errors
(called source errors) always exist, the fixtured workpiece
will consequently have position and/or orientation errors (called
resultant errors) that will definitely affect the final machining accuracy.
This paper illustrates a novel adaptive fixturing based on
active clamping forces for smart micropositioning of thin walled
precision parts. The aim of obtaining a modular unit, reusable
and exploitable to different industrial applications has been pursued
during the design phase. The proposed adaptive fixturing
device can lead to the following advantages:
- to perform an automatic errors-free workpiece clamping
and then drastically reduce the overall fixturing set up time;
- to recover unwanted strains induced on the workpiece, in
order to limit the amplitude of elastic strain recovery;
- to perform, if necessary, active vibration control (AVC) in
order to limit vibration/chatter effects induced by the cutting
tool
- …