11,487 research outputs found
Precision measurement of gravity with cold atoms in an optical lattice and comparison with a classical gravimeter
We report on a high precision measurement of gravitational acceleration using
ultracold strontium atoms trapped in a vertical optical lattice. Using
amplitude modulation of the lattice intensity, an uncertainty was reached by measuring at the 5 harmonic of the Bloch
oscillation frequency. After a careful analysis of systematic effects, the
value obtained with this microscopic quantum system is consistent with the one
we measured with a classical absolute gravimeter at the same location. This
result is of relevance for the recent interpretation of related experiments as
tests of gravitational redshift and opens the way to new tests of gravity at
micrometer scale.Comment: 4 pages, 4 figure
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
Rotation and Neoclassical Ripple Transport in ITER
Neoclassical transport in the presence of non-axisymmetric magnetic fields
causes a toroidal torque known as neoclassical toroidal viscosity (NTV). The
toroidal symmetry of ITER will be broken by the finite number of toroidal field
coils and by test blanket modules (TBMs). The addition of ferritic inserts
(FIs) will decrease the magnitude of the toroidal field ripple. 3D magnetic
equilibria with toroidal field ripple and ferromagnetic structures are
calculated for an ITER steady-state scenario using the Variational Moments
Equilibrium Code (VMEC). Neoclassical transport quantities in the presence of
these error fields are calculated using the Stellarator Fokker-Planck Iterative
Neoclassical Conservative Solver (SFINCS). These calculations fully account for
, flux surface shaping, multiple species, magnitude of ripple, and
collisionality rather than applying approximate analytic NTV formulae. As NTV
is a complicated nonlinear function of , we study its behavior over a
plausible range of . We estimate the toroidal flow, and hence , using
a semi-analytic turbulent intrinsic rotation model and NUBEAM calculations of
neutral beam torque. The NTV from the ripple dominates
that from lower perturbations of the TBMs. With the inclusion of FIs, the
magnitude of NTV torque is reduced by about 75% near the edge. We present
comparisons of several models of tangential magnetic drifts, finding
appreciable differences only for superbanana-plateau transport at small .
We find the scaling of calculated NTV torque with ripple magnitude to indicate
that ripple-trapping may be a significant mechanism for NTV in ITER. The
computed NTV torque without ferritic components is comparable in magnitude to
the NBI and intrinsic turbulent torques and will likely damp rotation, but the
NTV torque is significantly reduced by the planned ferritic inserts
Long-lived Bloch oscillations with bosonic Sr atoms and application to gravity measurement at micrometer scale
We report on the observation of Bloch oscillations on the unprecedented time
scale of severalseconds. The experiment is carried out with ultra-cold bosonic
strontium-88 loaded into a vertical optical standing wave. The negligible
atom-atom elastic cross section and the absence of spin makes Sr an
almost ideal Bose gas insensitive to typical mechanisms of decoherence due to
thermalization and to external stray fields. The small size enables precision
measurements of forces at micrometer scale. This is a challenge in physics for
studies of surfaces, Casimir effects, and searches for deviations from
Newtonian gravity predicted by theories beyond the standard model
Study of the spectral properties of ELM precursors by means of wavelets
The high confinement regime (H-mode) in tokamaks is accompanied by the occurrence of bursts of MHD activity at the plasma edge, so-called edge localized modes (ELMs), lasting less than 1 ms. These modes are often preceded by coherent oscillations in the magnetic field, the ELM precursors, whose mode numbers along the toroidal and the poloidal directions can be measured from the phase shift between Mirnov pickup coils. When the ELM precursors have a lifetime shorter than a few milliseconds, their toroidal mode number and their nonlinear evolution before the ELM crash cannot be studied reliably with standard techniques based on Fourier analysis, since averaging in time is implicit in the computation of the Fourier coefficients. This work demonstrates significant advantages in studying spectral features of the short-lived ELM precursors by using Morlet wavelets. It is shown that the wavelet analysis is suitable for the identification of the toroidal mode numbers of ELM precursors with the shortest lifetime, as well as for studying their nonlinear evolution with a time resolution comparable to the acquisition rate of the Mirnov coils
Selective enhancement of topologically induced interface states in a dielectric resonator chain
The recent realization of topological phases in insulators and
superconductors has advanced the quest for robust quantum technologies. The
prospects to implement the underlying topological features controllably has
given incentive to explore optical platforms for analogous realizations. Here
we realize a topologically induced defect state in a chain of dielectric
microwave resonators and show that the functionality of the system can be
enhanced by supplementing topological protection with non-hermitian symmetries
that do not have an electronic counterpart. We draw on a characteristic
topological feature of the defect state, namely, that it breaks a sublattice
symmetry. This isolates the state from losses that respect parity-time
symmetry, which enhances its visibility relative to all other states both in
the frequency and in the time domain. This mode selection mechanism naturally
carries over to a wide range of topological and parity-time symmetric optical
platforms, including couplers, rectifiers and lasers.Comment: 5 pages, 4 figures, + supplementary information (3 pages, 4 figures
Operationalizing the circular city model for naples' city-port: A hybrid development strategy
The city-port context involves a decisive reality for the economic development of territories and nations, capable of significantly influencing the conditions of well-being and quality of life, and of making the Circular City Model (CCM) operational, preserving and enhancing seas and marine resources in a sustainable way. This can be achieved through the construction of appropriate production and consumption models, with attention to relations with the urban and territorial system. This paper presents an adaptive decision-making process for Naples (Italy) commercial port's development strategies, aimed at re-establishing a sustainable city-port relationship and making Circular Economy (CE) principles operative. The approach has aimed at implementing a CCM by operationalizing European recommendations provided within both the Sustainable Development Goals (SDGs) framework-specifically focusing on goals 9, 11 and 12-and the Maritime Spatial Planning European Directive 2014/89, to face conflicts about the overlapping areas of the city-port through multidimensional evaluations' principles and tools. In this perspective, a four-step methodological framework has been structured applying a place-based approach with mixed evaluation methods, eliciting soft and hard knowledge domains, which have been expressed and assessed by a core set of Sustainability Indicators (SI), linked to SDGs. The contribution outcomes have been centred on the assessment of three design alternatives for the East Naples port and the development of a hybrid regeneration scenario consistent with CE and sustainability principles. The structured decision-making process has allowed us to test how an adaptive approach can expand the knowledge base underpinning policy design and decisions to achieve better outcomes and cultivate a broad civic and technical engagement, that can enhance the legitimacy and transparency of policies
A robust method for measurement of fluctuation parallel wavenumber in laboratory plasmas
Measuring the parallel wavenumber is fundamental for the experimental characterization of electrostatic instabilities. It becomes particularly important in toroidal geometry, where spatial inhomogeneities and curvature can excite both drift instabilities, whose wavenumber parallel to the magnetic field is finite, and interchange instabilities, which typically have vanishing parallel wavenumber. We demonstrate that multipoint measurements can provide a robust method for the discrimination between the two cases
Test of Einstein Equivalence Principle for 0-spin and half-integer-spin atoms: Search for spin-gravity coupling effects
We report on a conceptually new test of the equivalence principle performed
by measuring the acceleration in Earth's gravity field of two isotopes of
strontium atoms, namely, the bosonic Sr isotope which has no spin vs the
fermionic Sr isotope which has a half-integer spin. The effect of
gravity upon the two atomic species has been probed by means of a precision
differential measurement of the Bloch frequency for the two atomic matter waves
in a vertical optical lattice. We obtain the values for the E\"otv\"os parameter and
for the coupling between nuclear spin and gravity.
This is the first reported experimental test of the equivalence principle for
bosonic and fermionic particles and opens a new way to the search for the
predicted spin-gravity coupling effects.Comment: 5 pages, 4 figures. New spin-gravtity coupling analysis on the data
added to the manuscrip
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