260 research outputs found
Coherent excitation transport through ring-shaped networks
The coherent quantum transport of matter wave through a ring-shaped circuit
attached to leads defines an iconic system in mesoscopic physics that has
allowed both to explore fundamental questions in quantum science and to draw
important avenues for conceiving devices of practical use.
Here we study the source-to-drain transport of excitations going through a
ring-network, without propagation of matter waves. We model the circuit in
terms of a spin system with specific long-range interactions that are relevant
for quantum technology, such as Rydberg atoms trapped in optical tweezers or
ion traps. Inspired by the logic of rf- and dc-SQUIDs, we consider rings with
one and two local energy offsets, or detunings. As a combination of specific
phase shifts in going though the localized detunings and as a result of
coherent tunneling, we demonstrate how the transport of excitations can be
controlled, with a distinctive dependence on the range of interactions.Comment: Main text: 9 pages, 4 figures. Appendix: 16 pages, 10 figure
Influence of Tension Stiffening on the Flexural Stiffness of Reinforced Concrete Circular Sections
Within this paper, the assessment of tension stiffening effects on a reinforced concrete element with the circular sections subjected to axial and bending loads is presented. To this purpose, an enhancement of an analytical model already present within the actual technical literature is proposed. The accuracy of the enhanced method is assessed by comparing the experimental results carried out in past research and the numerical ones obtained by the model. Finally, a parametric study is executed in order to study the influence of axial compressive force on the flexural stiffness of reinforced concrete elements that are characterized by a circular section, comparing the secant stiffness evaluated at yielding and at maximum resistance, considering and not considering the effects of tension stiffness
Controlled flow of excitations in a ring-shaped network of Rydberg atoms
Highly excited Rydberg atoms are a powerful platform for quantum simulation
and information processing. Here, we propose atomic ring networks to study
chiral currents of Rydberg excitations. The currents are controlled by a phase
pattern imprinted via a Raman scheme and can persist even in the presence of
dephasing. Depending on the interplay between the Rabi coupling of Rydberg
states and the dipole-dipole atom interaction, the current shows markedly
different features. The excitations propagate with a velocity displaying a
characteristic peak in time, reflecting the chiral nature of the current. We
find that the time-averaged current in a quench behaves similarly to the
ground-state current. This analysis paves the way for the development of new
methods to transport information in atomic networks.Comment: 6 pages main, 6 figures + appendice
Statistical mechanics of the Cluster-Ising model
We study a Hamiltonian system describing a three-spin-1/2 cluster-like
interaction competing with an Ising-like anti-ferromagnetic interaction. We
compute free energy, spin correlation functions and entanglement both in the
ground and in thermal states. The model undergoes a quantum phase transition
between an Ising phase with a nonvanishing magnetization and a cluster phase
characterized by a string order. Any two-spin entanglement is found to vanish
in both quantum phases because of a nontrivial correlation pattern.
Neverthless, the residual multipartite entanglement is maximal in the cluster
phase and dependent on the magnetization in the Ising phase. We study the block
entropy at the critical point and calculate the central charge of the system,
showing that the criticality of the system is beyond the Ising universality
class.Comment: To be published in Physical Review
Chern-Simons theory and BCS superconductivity
We study the relationship between the holomorphic unitary connection of
Chern-Simons theory with temporal Wilson lines and the Richardson's exact
solution of the reduced BCS Hamiltonian. We derive the integrals of motion of
the BCS model, their eigenvalues and eigenvectors as a limiting case of the
Chern-Simons theory.Comment: 23 page
Quantum many particle systems in ring-shaped optical lattices
In the present work we demonstrate how to realize 1d-optical closed lattice
experimentally, including a {\it tunable} boundary phase-twist. The latter may
induce ``persistent currents'', visible by studing the atoms' momentum
distribution. We show how important phenomena in 1d-physics can be studied by
physical realization of systems of trapped atoms in ring-shaped optical
lattices. A mixture of bosonic and/or fermionic atoms can be loaded into the
lattice, realizing a generic quantum system of many interacting particles.Comment: 10 pages, 5 figures. To be published in PR
Spin wave contribution to entanglement in Heisenberg models
Employing the Holstein?Primakoff transformation, we obtain an approximate description of both the ground state entanglement and the entanglement dynamics in a spin system in terms of spin waves. As an example, we apply the method to a two-dimensional spin system
Malignancy as a risk factor in single-stage combined approach for simultaneous elective surgical diseases
AbstractObjectiveTo identify morbidity and mortality risk factors in patients with synchronous diseases who underwent single-stage combined (SSC) surgery.MethodsWe considered data of 328 patients, each with multiple, elective, synchronous surgical problems treated by a SSC operation. By univariate and multivariate analysis we evaluated many patient-, disease - or treatment-related variables with respect to post-operative mortality, morbidity, and hospital stay.ResultsTwo combined procedures were synchronously performed in 283 patients (86%), 3 combined procedures in 45 patients (14%). Post-operative mortality and morbidity rates were 3% and 24%, respectively, and median duration of hospital stay was 9 days. The occurrence of a surgical oncology procedure emerged as the most important independent risk factor for post-operative mortality and morbidity.ConclusionsThe safety of SSC surgery for the treatment of synchronous problems appears similar to that of multi-stage procedures. The understanding of risk factors for this surgical approach could be useful in order to improve patient selection
Multimodal validation of facial expression detection software for real-time monitoring of affect in patients with suicidal intent
We sought to test the hypothesis that previously validated biomarkers of high risk for suicide, namely EEG event related potentials (ERP), Galvanic skin response (GSR) and heart rate variability (HRV) can be employed in combination with facial affect and pupil dilation measures, in a novel diagnostic battery that will ultimately increase reliability of clinical evaluations of suicidal persons
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