2,431 research outputs found
Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit
Squeezing of quantum fluctuations by means of entanglement is a well
recognized goal in the field of quantum information science and precision
measurements. In particular, squeezing the fluctuations via entanglement
between two-level atoms can improve the precision of sensing, clocks,
metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically
relevant squeezing and entanglement for ~ 10^5 cold cesium atoms via a quantum
nondemolition (QND) measurement on the atom clock levels. We show that there is
an optimal degree of decoherence induced by the quantum measurement which
maximizes the generated entanglement. A two-color QND scheme used in this paper
is shown to have a number of advantages for entanglement generation as compared
to a single color QND measurement.Comment: 6 pages+suppl, PNAS forma
Partition function of the Potts model on self-similar lattices as a dynamical system and multiple transitions
We present an analytic study of the Potts model partition function on two
different types of self-similar lattices of triangular shape with non integer
Hausdorff dimension. Both types of lattices analyzed here are interesting
examples of non-trivial thermodynamics in less than two dimensions. First, the
Sierpinski gasket is considered. It is shown that, by introducing suitable
geometric coefficients, it is possible to reduce the computation of the
partition function to a dynamical system, whose variables are directly
connected to (the arising of) frustration on macroscopic scales, and to
determine the possible phases of the system. The same method is then used to
analyse the Hanoi graph. Again, dynamical system theory provides a very elegant
way to determine the phase diagram of the system. Then, exploiting the analysis
of the basins of attractions of the corresponding dynamical systems, we
construct various examples of self-similar lattices with more than one critical
temperature. These multiple critical temperatures correspond to crossing phases
with different degrees of frustration.Comment: 16 pages, 12 figures, 1 table; title changed, references and
discussion on multiple transitions adde
Fruit scent and observer colour vision shape food-selection strategies in wild capuchin monkeys
The senses play critical roles in helping animals evaluate foods, including fruits that can change both in colour and scent during ripening to attract frugivores. Although numerous studies have assessed the impact of colour on fruit selection, comparatively little is known about fruit scent and how olfactory and visual data are integrated during foraging. We combine 25 months of behavioural data on 75 wild, white-faced capuchins (Cebus imitator) with measurements of fruit colours and scents from 18 dietary plant species. We show that frequency of fruit-directed olfactory behaviour is positively correlated with increases in the volume of fruit odours produced during ripening. Monkeys with red-green colour blindness sniffed fruits more often, indicating that increased reliance on olfaction is a behavioural strategy that mitigates decreased capacity to detect red-green colour contrast. These results demonstrate a complex interaction among fruit traits, sensory capacities and foraging strategies, which help explain variation in primate behaviour.https://www.nature.com/articles/s41467-019-10250-9Published versio
Kauffman Knot Invariant from SO(N) or Sp(N) Chern-Simons theory and the Potts Model
The expectation value of Wilson loop operators in three-dimensional SO(N)
Chern-Simons gauge theory gives a known knot invariant: the Kauffman
polynomial. Here this result is derived, at the first order, via a simple
variational method. With the same procedure the skein relation for Sp(N) are
also obtained. Jones polynomial arises as special cases: Sp(2), SO(-2) and
SL(2,R). These results are confirmed and extended up to the second order, by
means of perturbation theory, which moreover let us establish a duality
relation between SO(+/-N) and Sp(-/+N) invariants. A correspondence between the
firsts orders in perturbation theory of SO(-2), Sp(2) or SU(2) Chern-Simons
quantum holonomies and the partition function of the Q=4 Potts Model is built.Comment: 20 pages, 7 figures; accepted for publication on Phys. Rev.
Coupling the valley degree of freedom to antiferromagnetic order
Conventional electronics are based invariably on the intrinsic degrees of
freedom of an electron, namely, its charge and spin. The exploration of novel
electronic degrees of freedom has important implications in both basic quantum
physics and advanced information technology. Valley as a new electronic degree
of freedom has received considerable attention in recent years. In this paper,
we develop the theory of spin and valley physics of an antiferromagnetic
honeycomb lattice. We show that by coupling the valley degree of freedom to
antiferromagnetic order, there is an emergent electronic degree of freedom
characterized by the product of spin and valley indices, which leads to
spin-valley dependent optical selection rule and Berry curvature-induced
topological quantum transport. These properties will enable optical
polarization in the spin-valley space, and electrical detection/manipulation
through the induced spin, valley and charge fluxes. The domain walls of an
antiferromagnetic honeycomb lattice harbors valley-protected edge states that
support spin-dependent transport. Finally, we employ first principles
calculations to show that the proposed optoelectronic properties can be
realized in antiferromagnetic manganese chalcogenophosphates (MnPX_3, X = S,
Se) in monolayer form.Comment: 6 pages, 5 figure
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