549 research outputs found
Squeezing and entangling nuclear spins in helium 3
We present a realistic model for transferring the squeezing or the
entanglement of optical field modes to the collective ground state nuclear spin
of He using metastability exchange collisions. We discuss in detail the
requirements for obtaining good quantum state transfer efficiency and study the
possibility to readout the nuclear spin state optically
A pulsed atomic soliton laser
It is shown that simultaneously changing the scattering length of an
elongated, harmonically trapped Bose-Einstein condensate from positive to
negative and inverting the axial portion of the trap, so that it becomes
expulsive, results in a train of self-coherent solitonic pulses. Each pulse is
itself a non-dispersive attractive Bose-Einstein condensate that rapidly
self-cools. The axial trap functions as a waveguide. The solitons can be made
robustly stable with the right choice of trap geometry, number of atoms, and
interaction strength. Theoretical and numerical evidence suggests that such a
pulsed atomic soliton laser can be made in present experiments.Comment: 11 pages, 4 figure
Enhanced and reduced atom number fluctuations in a BEC splitter
We measure atom number statistics after splitting a gas of ultracold 87Rb
atoms in a purely magnetic double-well potential created on an atom chip. Well
below the critical temperature for Bose-Einstein condensation T_c, we observe
reduced fluctuations down to -4.9dB below the atom shot noise level.
Fluctuations rise to more than +3.8dB close to T_c, before reaching the shot
noise level for higher temperatures. We use two-mode and classical field
simulations to model these results. This allows us to confirm that the
super-shot noise fluctuations directly originate from quantum statistics
Understanding mobility in a social petri dish
Despite the recent availability of large data sets on human movements, a full understanding of the rules governing motion within social systems is still missing, due to incomplete information on the socio-economic factors and to often limited spatio-temporal resolutions. Here we study an entire society of individuals, the players of an online-game, with complete information on their movements in a network-shaped universe and on their social and economic interactions. Such a "socio-economic laboratory" allows to unveil the intricate interplay of spatial constraints, social and economic factors, and patterns of mobility. We find that the motion of individuals is not only constrained by physical distances, but also strongly shaped by the presence of socio-economic areas. These regions can be recovered perfectly by community detection methods solely based on the measured human dynamics. Moreover, we uncover that long-term memory in the time-order of visited locations is the essential ingredient for modeling the trajectories
Long-lived quantum memory with nuclear atomic spins
We propose to store non-classical states of light into the macroscopic
collective nuclear spin ( atoms) of a He vapor, using
metastability exchange collisions. These collisions, commonly used to transfer
orientation from the metastable state to the ground state state of
He, can also transfer quantum correlations. This gives a possible
experimental scheme to map a squeezed vacuum field state onto a nuclear spin
state with very long storage times (hours).Comment: 4 page
Photo-physical characterization of fluorophore Ru(bpy)32+ for optical biosensing applications
We studied absorption, emission and lifetime of the coordination compound tris(2,2′-bipyridyl)ruthenium(II) fluorophore (Ru(bpy)32+) both dissolved in water solutions and dried. Lifetime measurements were carried out using a new detector, the Silicon Photomultiplier (SiPM), which is more sensitive and physically much smaller than conventional optical detectors, such as imager and scanner. Through these analyses and a morphological characterization with transmission electron microscopy, revealed its usability for sensor applications, in particular, as dye in optical DNA-chip technology, a viable alternative to the conventional CY5 fluorophore. The use of Ru(bpy)32+ would solve some of the typical disadvantages related to Cy5's application, such as self-absorption of fluorescence and photobleaching. In addition, the Ru(bpy)32+ longer lifetime may play a key role in the definition of new optical DNA-chip. Keywords: Tris(2,2′-bipyridyl)ruthenium(II), Fluorophore, Spectroscopy, Lifetime measurements, SiPM, TE
Influence of ewe feeding systems on carcass quality of suckling lambs
Numerous studies have evidenced significant differences in the carcass and meat quality of grass-fed and concentrate-fed lambs. The main differences regard carcass fatness (Murphy et al., 1994), subcutaneous fat colour (Prache and Theriez, 1999), meat colour (Priolo et al., 2002a) and fatty acid composition (Enser et al., 1998). The use of grazing in lamb feeding favours the presence of substances in the meat which are beneficial to human health. Different methods, based on the spectrophotometric properties of fat have been proposed to verify the origin of the product (Priolo et al., 2002b). The objective of the present study is to verify if and to what extent the carcass quality of suckling lambs is affected by ewe feeding systems
Simulations of thermal Bose fields in the classical limit
We demonstrate that the time-dependent projected Gross-Pitaevskii equation
derived earlier [Davis, et al., J. Phys. B 34, 4487 (2001)] can represent the
highly occupied modes of a homogeneous, partially-condensed Bose gas. We find
that this equation will evolve randomised initial wave functions to
equilibrium, and compare our numerical data to the predictions of a gapless,
second-order theory of Bose-Einstein condensation [S. A. Morgan, J. Phys. B 33,
3847 (2000)]. We find that we can determine the temperature of the equilibrium
state when this theory is valid.
Outside the range of perturbation theory we describe how to measure the
temperature of our simulations. We also determine the dependence of the
condensate fraction and specific heat on temperature for several interaction
strengths, and observe the appearance of vortex networks. As the
Gross-Pitaevskii equation is non-perturbative, we expect that it can describe
the correct thermal behaviour of a Bose gas as long as all relevant modes are
highly occupied.Comment: 15 pages, 12 figures, revtex4, follow up to Phys. Rev. Lett. 87
160402 (2001). v2: Modified after referee comments. Extra data added to two
figures, section on temperature determination expande
Microcanonical temperature for a classical field: application to Bose-Einstein condensation
We show that the projected Gross-Pitaevskii equation (PGPE) can be mapped
exactly onto Hamilton's equations of motion for classical position and momentum
variables. Making use of this mapping, we adapt techniques developed in
statistical mechanics to calculate the temperature and chemical potential of a
classical Bose field in the microcanonical ensemble. We apply the method to
simulations of the PGPE, which can be used to represent the highly occupied
modes of Bose condensed gases at finite temperature. The method is rigorous,
valid beyond the realms of perturbation theory, and agrees with an earlier
method of temperature measurement for the same system. Using this method we
show that the critical temperature for condensation in a homogeneous Bose gas
on a lattice with a UV cutoff increases with the interaction strength. We
discuss how to determine the temperature shift for the Bose gas in the
continuum limit using this type of calculation, and obtain a result in
agreement with more sophisticated Monte Carlo simulations. We also consider the
behaviour of the specific heat.Comment: v1: 9 pages, 5 figures, revtex 4. v2: additional text in response to
referee's comments, now 11 pages, to appear in Phys. Rev.
Emergence of good conduct, scaling and Zipf laws in human behavioral sequences in an online world
We study behavioral action sequences of players in a massive multiplayer
online game. In their virtual life players use eight basic actions which allow
them to interact with each other. These actions are communication, trade,
establishing or breaking friendships and enmities, attack, and punishment. We
measure the probabilities for these actions conditional on previous taken and
received actions and find a dramatic increase of negative behavior immediately
after receiving negative actions. Similarly, positive behavior is intensified
by receiving positive actions. We observe a tendency towards anti-persistence
in communication sequences. Classifying actions as positive (good) and negative
(bad) allows us to define binary 'world lines' of lives of individuals.
Positive and negative actions are persistent and occur in clusters, indicated
by large scaling exponents alpha~0.87 of the mean square displacement of the
world lines. For all eight action types we find strong signs for high levels of
repetitiveness, especially for negative actions. We partition behavioral
sequences into segments of length n (behavioral `words' and 'motifs') and study
their statistical properties. We find two approximate power laws in the word
ranking distribution, one with an exponent of kappa-1 for the ranks up to 100,
and another with a lower exponent for higher ranks. The Shannon n-tuple
redundancy yields large values and increases in terms of word length, further
underscoring the non-trivial statistical properties of behavioral sequences. On
the collective, societal level the timeseries of particular actions per day can
be understood by a simple mean-reverting log-normal model.Comment: 6 pages, 5 figure
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