838 research outputs found
Transport, atom blockade and output coupling in a Tonks-Girardeau gas
Recent experiments have demonstrated how quantum-mechanical impurities can be
created within strongly correlated quantum gases and used to probe the
coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M.
K\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a
phenomenological model to simulate such an output coupler for a Tonks-Girardeau
gas that shows qualitative agreement with the experimental results for atom
transport and output coupling. Our model allows us to explore nonequilibrium
transport phenomena in ultracold quantum gases and leads us to predict a regime
of atom blockade, where the impurity component becomes localized in the parent
cloud despite the presence of gravity. We show that this provides a stable
mixed-species quantum gas in the strongly correlated limit
An eccentrically perturbed Tonks-Girardeau gas
We investigate the static and dynamic properties of a Tonks-Girardeau gas in
a harmonic trap with an eccentric -perturbation of variable strength.
For this we first find the analytic eigensolution of the single particle
problem and use this solution to calculate the spatial density and energy
profiles of the many particle gas as a function of the strength and position of
the perturbation. We find that the crystal nature of the Tonks state is
reflected in both the lowest occupation number and momentum distribution of the
gas. As a novel application of our model, we study the time evolution of the
the spatial density after a sudden removal of the perturbation. The dynamics
exhibits collapses and revivals of the original density distribution which
occur in units of the trap frequency. This is reminiscent of the Talbot effect
from classical optics.Comment: Comments and suggestions are welcom
The pinning quantum phase transition in a Tonks Girardeau gas: diagnostics by ground state fidelity and the Loschmidt echo
We study the pinning quantum phase transition in a Tonks-Girardeau gas, both
in equilibrium and out-of-equilibrium, using the ground state fidelity and the
Loschmidt echo as diagnostic tools. The ground state fidelity (GSF) will have a
dramatic decrease when the atomic density approaches the commensurate density
of one particle per lattice well. This decrease is a signature of the pinning
transition from the Tonks to the Mott insulating phase. We study the
applicability of the fidelity for diagnosing the pinning transition in
experimentally realistic scenarios. Our results are in excellent agreement with
recent experimental work. In addition, we explore the out of equilibrium
dynamics of the gas following a sudden quench with a lattice potential. We find
all properties of the ground state fidelity are reflected in the Loschmidt echo
dynamics i.e., in the non equilibrium dynamics of the Tonks-Girardeau gas
initiated by a sudden quench of the lattice potential
Boson Pairs in a One-dimensional Split Trap
We describe the properties of a pair of ultracold bosonic atoms in a
one-dimensional harmonic trapping potential with a tunable zero-ranged barrier
at the trap centre. The full characterisation of the ground state is done by
calculating the reduced single-particle density, the momentum distribution and
the two-particle entanglement. We derive several analytical expressions in the
limit of infinite repulsion (Tonks-Girardeau limit) and extend the treatment to
finite interparticle interactions by numerical solution. As pair interactions
in double wells form a fundamental building block for many-body systems in
periodic potentials, our results have implications for a wide range of
problems.Comment: 9 pages, 8 figure
How Much Surveillance is Too Much? Some Thoughts on Surveillance, Democracy, and the Political Value of Privacy
Over the past decade it has become increasingly common to speak of the emergence of a surveillance society. Surveillance is an almost inescapable part of 21st century life. There is a very real danger that individual privacy - as it is currently understood - may soon become a thing of the past. Some would argue privacy is already dead and we have no choice but to accept our newly transparent lives. For many, surveillance has become part of daily life during visit banks, stores, shopping malls, and many public streets and parks. Travel through airports subjects our bodies to physical scans and our passports to electronic scrutiny. Attendees of public gatherings and demonstrations are often overtly captured on police CCTV video cameras. Perhaps the most profound expansion of surveillance has been in the area of dataveillance. Both the state and the private sector routinely require individuals to hand over large amounts of personal information as a matter of law or in exchange for access to services. The private sector owns vast amounts of information about us and processes and shares that information to create consumer profiles capable of accurately predicting individual consumption preferences. The intrusion of surveillance and dataveillance into every aspect of our lives hampers the degree to which individuals are able to construct and control different context-specific social identities. Our ability to function in society rests partly on our ability to keep these social roles separate. surveillance posses a very real threat to teh possibility of living complex, multi-layered social lives. This chapter considers question of how surveillance might affect the proper functioning of the rule of law, and the related question of how much surveillance is too much in a democratic society. The author considers: (1) the role of privacy in the protection of political rights; and (2) how much surveillance is too much
Surveillance and the Political Value of Privacy
The steady expansion in the use of surveillance technologies by the state and private sector represents a substantial threat to the privacy of ordinary individuals. Yet despite the best efforts of civil libertarians, many members of the public still struggle to understand why privacy is valuable and deserves to be protected as a basic right. In part, this is a result of the inherent complexity of the idea of privacy, but it is also due a tendency on the part of privacy advocates to focus on the individual - as opposed to the social and political dimensions - of privacy. In order to ensure that there is a greater level of public engagement with matters of privacy and sufficient awareness of the dangers of intrusive surveillance, more must be done to ensure that the general public appreciates that privacy is not just essential for individual freedom, but also for the health of society as a whole
CCTV and Human Rights
This chapter provides a brief overview of the human rights implications of closed circuit television (CCTV) surveillance, and aims to help CCTV managers and operators develop public area surveillance policies and practices that are consistent with a commitment to the protection of individual rights and a respect for civil liberties
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