2,650 research outputs found
Plasma fluctuations in a Kaufman thruster
Measurements of the RMS magnitude, spectra, and cross correlations for the fluctuations in the beam, discharge, and neutralizer keeper currents are presented for a 30 cm diameter dished grid ion thruster for a range of magnetic baffle currents. The ratio of RMS to mean ion beam current varied from 0.04 to 0.23. The spectra of the amplitudes of the beam and discharge current fluctuations were taken up to 9 MHz and show that the predominant amplitudes occur at frequencies of 10 kHz or below. The falloff with increasing frequency is rapid. Frequencies above 100 kHz the spectral levels are 45 kb or more below the maximum peak amplitudes. The cross correlations revealed the ion beam fluctuations to have large radial and axial scales
Gravimetry through non-linear optomechanics
We propose a new method for measurements of gravitational acceleration using
a quantum optomechanical system. As a proof-of-concept, we investigate the
fundamental sensitivity for a cavity optomechanical system for gravitational
accelerometry with a light-matter interaction of the canonical `trilinear'
radiation pressure form. The phase of the optical output of the cavity encodes
the gravitational acceleration and is the only component which needs to be
measured to perform the gravimetry. We analytically show that homodyne
detection is the optimal readout in our scheme, based on the cyclical
decoupling of light and matter, and predict a fundamental sensitivity of
ms for currently achievable optomechanical systems
which could, in principle, surpass the best atomic interferometers even for low
optical intensities. Our scheme is strikingly robust to the initial thermal
state of the mechanical oscillator as the accumulated gravitational phase only
depends on relative position separation between components of the entangled
optomechanical state arising during the evolution.Comment: 14 pages, 15 figure
Quantum cooling and squeezing of a levitating nanosphere via time-continuous measurements
With the purpose of controlling the steady state of a dielectric nanosphere
levitated within an optical cavity, we study its conditional dynamics under
simultaneous sideband cooling and additional time-continuous measurement of
either the output cavity mode or the nanosphere's position. We find that the
average phonon number, purity and quantum squeezing of the steady-states can
all be made more non-classical through the addition of time-continuous
measurement. We predict that the continuous monitoring of the system, together
with Markovian feedback, allows one to stabilize the dynamics for any value of
the laser frequency driving the cavity. By considering state-of-the-art values
of the experimental parameters, we prove that one can in principle obtain a
non-classical (squeezed) steady-state with an average phonon number .Comment: 10 pages, 9 figures; v2: close to published versio
Decoherence of number states in phase-sensitive reservoirs
The non-unitary evolution of initial number states in general Gaussian
environments is solved analytically. Decoherence in the channels is quantified
by determining explicitly the purity of the state at any time. The influence of
the squeezing of the bath on decoherence is discussed. The behavior of coherent
superpositions of number states is addressed as well.Comment: 5 pages, 2 figures, minor changes, references adde
Electrophysiological correlates of unconscious processes of race
The study aimed to examine the neural mechanisms underlying implicit other-race face processing by the use of the masked and unmasked priming manipulation. Two types of prime-target pairs were presented while recording Event-related potentials (ERPs): Same face pairs (prime-target were identical faces), and Different face pairs (prime-target were different faces). Prime-target pairs were half Asian (other-race) and half Caucasian (own-race) faces. The face stimuli on each pair were of the same gender and race. Participants (all Caucasians) had to decide whether the target was a male or a female face (gender task). The prime face could be unmasked or masked. On the behavioral side, our findings showed a race effect, that is slower reaction times (RTs) for other-race than own-race face stimuli, regardless of masking. On the ERPs side, our data showed a race effect across all components analyzed (P100, N100, N200, P300), under both the unmasked and masked manipulations. Besides, we found, in the unmasked condition, a priming effect as a function of race on the N100, N200, and P300 components; but, interestingly, in the masked condition, only on the P300. Overall, our findings provide evidence that race information is available very early in the brain and can strongly activate and influence people’s behaviors even without conscious awareness
Observation of a Spinning Top in a Bose-Einstein Condensate
Boundaries strongly affect the behavior of quantized vortices in
Bose-Einstein condensates, a phenomenon particularly evident in elongated
cigar-shaped traps where vortices tend to orient along a short direction to
minimize energy. Remarkably, contributions to the angular momentum of these
vortices are tightly confined to the region surrounding the core, in stark
contrast to untrapped condensates where all atoms contribute . We
develop a theoretical model and use this, in combination with numerical
simulations, to show that such localized vortices precess in an analogous
manner to that of a classical spinning top. We experimentally verify this
spinning-top behavior with our real-time imaging technique that allows for the
tracking of position and orientation of vortices as they dynamically evolve.
Finally, we perform an in-depth numerical investigation of our real-time
expansion and imaging method, with the aim of guiding future experimental
implementation, as well as outlining directions for its improvement.Comment: 10 pages, 7 figure
Isoflavones and other compounds from the roots of Iris marsica I. Ricci E Colas. Collected from Majella National Park, Italy
In this study, a phytochemical analysis was performed, for the first time, on Iris marsica I. Ricci e Colas. In particular, the attention was focused on the constituents of the roots. Twenty-one compounds were isolated by column chromatography and were analyzed/identified by NMR spectroscopy and mass spectrometry. They all own chemotaxonomic, ethno-pharmacological and nutraceutical relevance which allowed us to provide a phytochemical rationale, for the correct botanical classification of this species, for the employment of its roots in folk medicine like for all the other species belonging to the Iris genus and, lastly, for their further uses as food with important healthy benefits. All of these parts were broadly discussed about within the text
Passing quantum correlations to qubits using any two-mode state
We draw an explicit connection between the statistical properties of an
entangled two-mode continuous variable (CV) resource and the amount of
entanglement that can be dynamically transferred to a pair of non-interacting
two-level systems. More specifically, we rigorously reformulate entanglement
transfer process by making use of covariance matrix formalism. When the
resource state is Gaussian, our method makes the approach to the transfer of
quantum correlations much more flexible than in previously considered schemes
and allows the straightforward inclusion of the effects of noise affecting the
CV system. Moreover, the proposed method reveals that the use of de-Gaussified
two-mode states is almost never advantageous for transferring entanglement with
respect to the full Gaussian picture, despite the entanglement in the
non-Gaussian resource can be much larger than in its Gaussian counterpart. We
can thus conclude that the entanglement-transfer map overthrows the "ordering"
relations valid at the level of CV resource states.Comment: 10 pages, 6 figures, RevTeX4, Accepted for publication in Physical
Review
Entanglement dynamics of bipartite system in squeezed vacuum reservoirs
Entanglement plays a crucial role in quantum information protocols, thus the
dynamical behavior of entangled states is of a great importance. In this paper
we suggest a useful scheme that permits a direct measure of entanglement in a
two-qubit cavity system. It is realized in the cavity-QED technology utilizing
atoms as fying qubits. To quantify entanglement we use the concurrence. We
derive the conditions, which assure that the state remains entangled in spite
of the interaction with the reservoir. The phenomenon of sudden death
entanglement (ESD) in a bipartite system subjected to squeezed vacuum reservoir
is examined. We show that the sudden death time of the entangled states depends
on the initial preparation of the entangled state and the parameters of the
squeezed vacuum reservoir.Comment: 10 pages, 5 figures, CEWQO17(St Andrews
- …