513 research outputs found
Coherent transport of atomic wave packets in amplitude-modulated vertical optical lattices
We report on the realization of dynamical control of transport for ultra-cold
Sr88 atoms loaded in an accelerated and amplitude-modulated 1D optical lattice.
We tailor the energy dispersion of traveling wave packets and reversibly switch
between Wannier-Stark localization and driven transport based on coherent
tunneling. Within a Loschmidt-echo scheme where the atomic group velocities are
reversed at once, we demonstrate a novel mirror for matter waves working
independently of the momentum state and discuss possible applications to force
measurements at micrometric scales
Superfluid and Dissipative Dynamics of a Bose-Einstein Condensate in a Periodic Optical Potential
We create Bose-Einstein condensates of 87-rubidium in a static magnetic trap
with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic
trap center we are able to control the condensate evolution. We observe a
change in the frequency of the center-of-mass oscillation in the harmonic
trapping potential, in analogy with an increase in effective mass. For fluid
velocities greater than a local speed of sound, we observe the onset of
dissipative processes up to full removal of the superfluid component. A
parallel simulation study visualizes the dynamics of the BEC and accounts for
the main features of the observed behavior.Comment: 4 pages, including figure
Effect of inter-well interactions on non-linear beam splitters for matter-wave interferometers
We study the non-linear beam splitter in matter-wave interferometers using ultracold quantum gases in a double-well configuration in presence of non-local interactions inducing inter-well density-density coupling, as they can be realized, e.g., with dipolar gases. We explore this effect after considering different input states, in the form of either coherent, or Twin-Fock, or NOON states. We first review the non-interacting limit and the case in which only the local interaction is present, including the study of sensitivity near the self-trapping threshold. Then, we consider the two-mode model in the presence of inter-well interactions and consider the scaling of the sensitivity as a function of the non-local coupling strength. Our analysis clearly shows that non-local interactions can compensate the degradation of the sensitivity induced by local interactions, so that they may be used to restore optimal sensitivity
Released momentum distribution of a Fermi gas in the BCS-BEC crossover
We develop a time-dependent mean-field theory to investigate the released
momentum distribution and the released energy of an ultracold Fermi gas in the
BCS-BEC crossover after the scattering length has been set to zero by a fast
magnetic-field ramp. For a homogeneous gas we analyze the non-equilibrium
dynamics of the system as a function of the interaction strength and of the
ramp speed. For a trapped gas the theoretical predictions are compared with
experimental results.Comment: 4 pages, 4 figure
A decrease of calcitonin serum concentrations less than 50 percent 30 minutes after thyroid surgery suggests incomplete C-cell tumor tissue removal
The prognosis of medullary thyroid carcinoma (MTC) depends on the completeness of the first surgical treatment. To date, it is not possible to predict whether the tumor has been completely removed after surgery. The aim of this study was to evaluate the reliability of an intraoperative calcitonin monitoring as a predictor of the final outcome after surgery in patients with MTC
Effects of atomic interactions on the resonant tunneling of sodium condensates
4noWe investigate the influence of atomic interactions on the tunnelling of sodium condensates across a spatially oscillating optical barrier. In the limit of very fast barrier oscillations, in which resonant tunnelling via a metastable state takes place, the interactions affect the position and lineshape of the transmission peak. We anticipate that the possibility of modulating the interactions in a tunnelling condensate can be exploited to achieve nonlinear effects such as optical limiting and bistability.openopenD. EMBRIACO; M. L. CHIOFALO; M. ARTONI; AND G. C. LA ROCCAD., Embriaco; M. L., Chiofalo; Artoni, Maurizio; AND G. C., LA ROCC
Dynamical Superfluid-Insulator Transition in a Chain of Weakly Coupled Bose-Einstein Condensates
We predict a dynammical classical superfluid-insulator transition (CSIT) in a
Bose-Einstein condensate (BEC) trapped in an optical and a magnetic potential.
In the tight-binding limit, this system realizes an array of weakly-coupled
condensates driven by an external harmonic field. For small displacements of
the parabolic trap about the equilibrium position, the BEC center of mass
oscillates with the relative phases of neighbouring condensates locked at the
same (oscillating) value. For large displacements, the BEC remains localized on
the side of the harmonic trap. This is caused by a randomization of the
relative phases, while the coherence of each individual condensate in the array
is preserved. The CSIT is attributed to a discrete modulational instability,
occurring when the BEC center of mass velocity is larger than a critical value,
proportional to the tunneling rate between adjacent sites.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let
Alkaline phosphatase survey in pecorino siciliano PDO cheese
The determination of alkaline phosphatase (ALP) in cheeses has become an official method for controlling cheeses with a protected designation of origin (PDO), all of which use raw milk. PDO cheeses, characterized by high craftsmanship, usually have an uneven quality. However, for these cheeses, it is necessary to establish ALP values so that they can be defined as a raw milk product. In this study, a dataset with Pecorino Siciliano PDO samples was analyzed to determine ALP both at the core and under the rind. The results showed that there was no significant difference between the different zones in Pecorino cheese. A second dataset of 100 pecorino cheese samples determined that ALP was only at the core of the cheese. Moreover, there was a statistically significant difference between the ALP values of cheeses produced with raw milk and those produced with pasteurized milk. Furthermore, according to the temperatures, a wide variability of ALP values was observed in the Pecorino Siciliano PDO samples from the core of the cheeses. This was a result of several under scotta whey cooking methodologies adopted by cheesemakers, which do not permit a clear range. Therefore, further investigation is desirable
Dynamical response of the "GGG" rotor to test the Equivalence Principle: theory, simulation and experiment. Part I: the normal modes
Recent theoretical work suggests that violation of the Equivalence Principle
might be revealed in a measurement of the fractional differential acceleration
between two test bodies -of different composition, falling in the
gravitational field of a source mass- if the measurement is made to the level
of or better. This being within the reach of ground based
experiments, gives them a new impetus. However, while slowly rotating torsion
balances in ground laboratories are close to reaching this level, only an
experiment performed in low orbit around the Earth is likely to provide a much
better accuracy.
We report on the progress made with the "Galileo Galilei on the Ground" (GGG)
experiment, which aims to compete with torsion balances using an instrument
design also capable of being converted into a much higher sensitivity space
test.
In the present and following paper (Part I and Part II), we demonstrate that
the dynamical response of the GGG differential accelerometer set into
supercritical rotation -in particular its normal modes (Part I) and rejection
of common mode effects (Part II)- can be predicted by means of a simple but
effective model that embodies all the relevant physics. Analytical solutions
are obtained under special limits, which provide the theoretical understanding.
A simulation environment is set up, obtaining quantitative agreement with the
available experimental data on the frequencies of the normal modes, and on the
whirling behavior. This is a needed and reliable tool for controlling and
separating perturbative effects from the expected signal, as well as for
planning the optimization of the apparatus.Comment: Accepted for publication by "Review of Scientific Instruments" on Jan
16, 2006. 16 2-column pages, 9 figure
Delocalization-enhanced Bloch oscillations and driven resonant tunneling in optical lattices for precision force measurements
In this paper we describe and compare different methods used for accurate
determination of forces acting on matter-wave packets in optical lattices. The
quantum interference nature responsible for the production of both Bloch
oscillations and coherent delocalization is investigated in detail. We study
conditions for optimal detection of Bloch oscillation for a thermal ensemble of
cold atoms with a large velocity spread. We report on the experimental
observation of resonant tunneling in an amplitude-modulated (AM) optical
lattice up to the sixth harmonic with Fourier-limited linewidth. We then
explore the fundamental and technical phenomena which limit both the
sensitivity and the final accuracy of the atomic force sensor at 10^{-7}
precision level [1], with an analysis of the coherence time of the system and
addressing few simple setup changes to go beyond the current accuracy.Comment: 18 pages, 10 figure
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