3,742 research outputs found
Dynamic formation of Rydberg aggregates at off-resonant excitation
The dynamics of a cloud of ultra-cold two-level atoms is studied at
off-resonant laser driving to a Rydberg state. We find that resonant excitation
channels lead to strongly peaked spatial correlations associated with the
buildup of asymmetric excitation structures. These aggregates can extend over
the entire ensemble volume, but are in general not localized relative to the
system boundaries. The characteristic distances between neighboring excitations
depend on the laser detuning and on the interaction potential. These properties
lead to characteristic features in the spatial excitation density, the Mandel
parameter, and the total number of excitations. As an application an
implementation of the three-atom CSWAP or Fredkin gate with Rydberg atoms is
discussed. The gate not only exploits the Rydberg blockade, but also utilizes
the special features of an asymmetric geometric arrangement of the three atoms.
We show that continuous-wave off-resonant laser driving is sufficient to create
the required spatial arrangement of atoms out of a homogeneous cloud.Comment: 8 pages, 7 figure
Exploring eCourt innovations in New South Wales civil courts
Some New South Wales civil courts have recently introduced electronic filing and online pre-trial appearances. These innovations have different consequences for different users of the civil justice system. Whatever the ostensible benefit, any change to the way our justice system works must enable the purpose for which it exists: access to justice. For practitioners and self-represented litigants who would otherwise travel long distances to attend court, the time and costs savings could be significant. Of course, this intended outcome depends upon the reliability and usability of the technology, as well as the competence of the users. However, for those without these skills or those who do not have access to computers and/or the internet, this change could impede access to justice. It is too early to evaluate the success of this project, but lessons can be drawn from other jurisdictions. This article will explore potential advantages and disadvantages of these changes for self-represented litigants and legal professionals. It will conclude that as technology is disrupting all aspects of our social and commercial arrangements, it is logical that our courts will need to keep up
Superconductivity in Pseudo-Binary Silicide SrNixSi2-x with AlB2-Type Structure
We demonstrate the emergence of superconductivity in pseudo-binary silicide
SrNixSi2-x. The compound exhibits a structural phase transition from the cubic
SrSi2-type structure (P4132) to the hexagonal AlB2-type structure (P6/mmm) upon
substituting Ni for Si at approximately x = 0.1. The hexagonal structure is
stabilized in the range of 0.1 < x < 0.7. The superconducting phase appears in
the vicinity of the structural phase boundary. Ni acts as a nonmagnetic dopant,
as confirmed by the Pauli paramagnetic behavior.Comment: 12 pages, 5 figure
Lowering of surface melting temperature in atomic clusters with a nearly closed shell structure
We investigate the interplay of particle number, N, and structural properties
of selected clusters with N=12 up to N=562 by employing Gupta potentials
parameterized for Aluminum and extensive Monte-Carlo simulations. Our analysis
focuses on closed shell structures with extra atoms. The latter can put the
cluster under a significant stress and we argue that typically such a strained
system exhibits a reduced energy barrier for (surface) diffusion of cluster
atoms. Consequently, also its surface melting temperature, T_S, is reduced, so
that T_S separates from and actually falls well below the bulk value. The
proposed mechanism may be responsible for the suppression of the surface
melting temperature observed in a recent experiments.Comment: 9 pages, 7 figures, 1 table, REVTeX 4; submitted to Phys.Rev.
Effect of retardation on the dynamics of entanglement between atoms
The role of retardation in the entanglement dynamics of two distant atoms
interacting with a multi-mode field of a ring cavity is discussed. The
retardation is associated with a finite time required for light to travel
between the atoms located at a finite distance and between the atoms and the
cavity boundaries. We explore features in the concurrence indicative of
retardation and show how these features evolve depending on the initial state
of the system, distance between the atoms and the number of modes to which the
atoms are coupled. In particular, we consider the short-time and the long time
dynamics for both the multi- and sub-wavelength distances between the atoms. It
is found that the retardation effects can qualitatively modify the entanglement
dynamics of the atoms not only at multi- but also at sub-wavelength distances.
We follow the temporal evolution of the concurrence and find that at short
times of the evolution the retardation induces periodic sudden changes of
entanglement. To analyze where the entanglement lies in the space spanned by
the state vectors of the system, we introduce the collective Dicke states of
the atomic system that explicitly account for the sudden changes as a periodic
excitation of the atomic system to the maximally entangled symmetric state. At
long times, the retardation gives rise to periodic beats in the concurrence
that resemble the phenomenon of collapses and revivals in the Jaynes-Cummings
model. In addition, we identify parameter values and initial conditions at
which the atoms remain separable or are entangled without retardation during
the entire evolution time, but exhibit the phenomena of sudden birth and sudden
death of entanglement when the retardation is included.Comment: 16 pages, 14 figure
Two-mode single-atom laser as a source of entangled light
A two-mode single-atom laser is considered, with the aim of generating
entanglement in macroscopic light. Two transitions in the four-level gain
medium atom independently interact with the two cavity modes, while two other
transitions are driven by control laser fields. Atomic relaxation as well as
cavity losses are taken into account. We show that this system is a source of
macroscopic entangled light over a wide range of control parameters and initial
states of the cavity field
On the design of an energy-efficient low-latency integrated protocol for distributed mobile sensor networks
Self organizing, wireless sensors networks are an emergent and challenging technology that is attracting large attention in the sensing and monitoring community. Impressive progress has been done in recent years even if we need to assume that an optimal protocol for every kind of sensor network applications can not exist. As a result it is necessary to optimize the protocol for certain scenarios. In many applications for instance latency is a crucial factor in addition to energy consumption. MERLIN performs its best in such WSNs where there is the need to reduce the latency while ensuring that energy consumption is kept to a minimum. By means of that, the low latency characteristic of MERLIN can be used as a trade off to extend node lifetimes. The performance in terms of energy consumption and latency is optimized by acting on the slot length. MERLIN is designed specifically to integrate routing, MAC and localization protocols together. Furthermore it can support data queries which is a typical application for WSNs. The MERLIN protocol eliminates the necessity to have any explicit handshake mechanism among nodes. Furthermore, the reliability is improved using multiple path message propagation in combination with an overhearing mechanism. The protocol divides the network into subsets where nodes are grouped in time zones. As a result MERLIN also shows a good scalability by utilizing an appropriate scheduling mechanism in combination with a contention period
Microcavities coupled to multilevel atoms
A three-level atom in the -configuration coupled to a microcavity is
studied. The two transitions of the atom are assumed couple to different
counterpropagating mode pairs in the cavity. We analyze the dynamics both, in
the strong-coupling and the bad cavity limit. We find that compared to a
two-level setup, the third atomic state and the additional control field modes
crucially modify the system dynamics and enable more advanced control schemes.
All results are explained using appropriate dressed state and eigenmode
representations. As potential applications, we discuss optical switching and
turnstile operations and detection of particles close to the resonator surface.Comment: 14 pages, 9 figure
Universal time-evolution of a Rydberg lattice gas with perfect blockade
We investigate the dynamics of a strongly interacting spin system that is
motivated by current experimental realizations of strongly interacting Rydberg
gases in lattices. In particular we are interested in the temporal evolution of
quantities such as the density of Rydberg atoms and density-density
correlations when the system is initialized in a fully polarized state without
Rydberg excitations. We show that in the thermodynamic limit the expectation
values of these observables converge at least logarithmically to universal
functions and outline a method to obtain these functions. We prove that a
finite one-dimensional system follows this universal behavior up to a given
time. The length of this universal time period depends on the actual system
size. This shows that already the study of small systems allows to make precise
predictions about the thermodynamic limit provided that the observation time is
sufficiently short. We discuss this for various observables and for systems
with different dimensions, interaction ranges and boundary conditions.Comment: 16 pages, 3 figure
Anderson Transitions: Criticality, Symmetries, and Topologies
The physics of Anderson transitions between localized and metallic phases in
disordered systems is reviewed. We focus on the character of criticality as
well as on underlying symmetries and topologies that are crucial for
understanding phase diagrams and the critical behavior.Comment: 36 pages. Published in "50 Years of Anderson Localization", ed. by E.
Abrahams (World Scientific, 2010); reprinted in IJMP
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