19,197 research outputs found
Entanglement scaling at first order phase transitions
First order quantum phase transitions (1QPTs) are signaled, in the
thermodynamic limit, by discontinuous changes in the ground state properties.
These discontinuities affect expectation values of observables, including
spatial correlations. When a 1QPT is crossed in the vicinity of a second order
one (2QPT), due to the correlation length divergence of the latter, the
corresponding ground state is modified and it becomes increasingly difficult to
determine the order of the transition when the size of the system is finite.
Here we show that, in such situations, it is possible to apply finite size
scaling to entanglement measures, as it has recently been done for the order
parameters and the energy gap, in order to recover the correct thermodynamic
limit. Such a finite size scaling can unambigously discriminate between first
and second order phase transitions in the vicinity of multricritical points
even when the singularities displayed by entanglement measures lead to
controversial results
The Overlap between Headache and Epilepsy in the Light of Recent Advances in Medical Genetics
Not Available
Probing magnetic order in ultracold lattice gases
A forthcoming challenge in ultracold lattice gases is the simulation of
quantum magnetism. That involves both the preparation of the lattice atomic gas
in the desired spin state and the probing of the state. Here we demonstrate how
a probing scheme based on atom-light interfaces gives access to the order
parameters of nontrivial quantum magnetic phases, allowing us to characterize
univocally strongly correlated magnetic systems produced in ultracold gases.
This method, which is also nondemolishing, yields spatially resolved spin
correlations and can be applied to bosons or fermions. As a proof of principle,
we apply this method to detect the complete phase diagram displayed by a chain
of (rotationally invariant) spin-1 bosons.Comment: published versio
Increasing entanglement through engineered disorder in the random Ising chain
The ground state entanglement entropy between block of sites in the random
Ising chain is studied by means of the Von Neumann entropy. We show that in
presence of strong correlations between the disordered couplings and local
magnetic fields the entanglement increases and becomes larger than in the
ordered case. The different behavior with respect to the uncorrelated
disordered model is due to the drastic change of the ground state properties.
The same result holds also for the random 3-state quantum Potts model.Comment: 4 pages, published version, a few typos correcte
Measuring work and heat in ultracold quantum gases
We propose a feasible experimental scheme to direct measure heat and work in
cold atomic setups. The method is based on a recent proposal which shows that
work is a positive operator valued measure (POVM). In the present contribution,
we demonstrate that the interaction between the atoms and the light
polarisation of a probe laser allows us to implement such POVM. In this way the
work done on or extracted from the atoms after a given process is encoded in
the light quadrature that can be measured with a standard homodyne detection.
The protocol allows one to verify fluctuation theorems and study properties of
the non-unitary dynamics of a given thermodynamic process.Comment: Published version in the Focus Issue on "Quantum Thermodynamics
Witnesses of non-classicality for simulated hybrid quantum systems
The task of testing whether quantum theory applies to all physical systems
and all scales requires considering situations where a quantum probe interacts
with another system that need not obey quantum theory in full. Important
examples include the cases where a quantum mass probes the gravitational field,
for which a unique quantum theory of gravity does not yet exist, or a quantum
field, such as light, interacts with a macroscopic system, such as a biological
molecule, which may or may not obey unitary quantum theory. In this context a
class of experiments has recently been proposed, where the non-classicality of
a physical system that need not obey quantum theory (the gravitational field)
can be tested indirectly by detecting whether or not the system is capable of
entangling two quantum probes. Here we illustrate some of the subtleties of the
argument, to do with the role of locality of interactions and of
non-classicality, and perform proof-of-principle experiments illustrating the
logic of the proposals, using a Nuclear Magnetic Resonance quantum
computational platform with four qubits.Comment: Revised and extende
Smart technologies: useful tools to assess the exposure to solar ultraviolet radiation for general population and outdoor workers
Beside some documented benefits attributed to ultraviolet solar radiation (solar UVR), a lot of adverse effects are a consequence of a chronic exposure, including the occurrence of photo-induced skin cancer. Improvement in risks perception, due to UVR overexposure, in the case of occupational or recreational exposure, is of great importance for public health. The amount of exposure to UVR has to be assessed as accurately as possible, with the aim to characterize different exposure conditions and, by their appropriate management, to prevent adverse health effects attributed to prolonged exposure to solar radiation (SR). The available technology allows to acquire such information, either using miniaturized and wearable sensors, or through devices who exploit radiative transfer models by integrating satellite-based radiometric data with meteorological data. We proceeded to an intercomparison to evaluate the performance of different devices in three commonly exposure conditions. Applications using satellite data, developed for preventing sunburn during recreational exposure, are adeguate for that purpose, while for a more accurate exposure assessment, only those which evaluate the irradiance in near real-time provide acceptable results. Unlike earlier, the low-cost devices that use wearable sensors showed inadequate performance for our purpose
Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism
The non-equilibrium dynamics of an ion chain in a highly anisotropic trap is
studied when the transverse trap frequency is quenched across the value at
which the chain undergoes a continuous phase transition from a linear to a
zigzag structure. Within Landau theory, an equation for the order parameter,
corresponding to the transverse size of the zigzag structure, is determined
when the vibrational motion is damped via laser cooling. The number of
structural defects produced during a linear quench of the transverse trapping
frequency is predicted and verified numerically. It is shown to obey the
scaling predicted by the Kibble-Zurek mechanism, when extended to take into
account the spatial inhomogeneities of the ion chain in a linear Paul trap.Comment: 5 pages, 3 figure
- …