19,132 research outputs found
Coexistence of different scaling laws for the entanglement entropy in a periodically driven system
The out-of-equilibrium dynamics of many body systems has recently received a
burst of interest, also due to experimental implementations. The dynamics of
both observables, such as magnetization and susceptibilities, and quantum
information related quantities, such as concurrence and entanglement entropy,
have been investigated under different protocols bringing the system out of
equilibrium. In this paper we focus on the entanglement entropy dynamics under
a sinusoidal drive of the transverse magnetic field in the 1D quantum Ising
model. We find that the area and the volume law of the entanglement entropy
coexist under periodic drive for an initial non-critical ground state.
Furthermore, starting from a critical ground state, the entanglement entropy
exhibits finite size scaling even under such a periodic drive. This
critical-like behaviour of the out-of-equilibrium driven state can persist for
arbitrarily long time, provided that the entanglement entropy is evaluated on
increasingly subsystem sizes, whereas for smaller sizes a volume law holds.
Finally, we give an interpretation of the simultaneous occurrence of critical
and non-critical behaviour in terms of the propagation of Floquet
quasi-particles.Comment: contribution to the 11th Italian Quantum Information Science
conference (IQIS), September 17th-20th, 2018 - Catania, Italy, 4 page
Composite quantum collision models
A collision model (CM) is a framework to describe open quantum dynamics. In
its {\it memoryless} version, it models the reservoir as
consisting of a large collection of elementary ancillas: the dynamics of the
open system results from successive "collisions" of
with the ancillas of . Here, we present a general formulation of
memoryless {\it composite} CMs, where is partitioned into the very
open system under study coupled to one or more auxiliary systems .
Their composite dynamics occurs through internal - collisions
interspersed with external ones involving and the reservoir . We show that important known instances of quantum {\it non-Markovian}
dynamics of -- such as the emission of an atom into a reservoir featuring a
Lorentzian, or multi-Lorentzian, spectral density or a qubit subject to random
telegraph noise -- can be mapped on to such {\it memoryless} composite CMs.Comment: 12 pages, 4 figure
Class of exact memory-kernel master equations
A well-known situation in which a non-Markovian dynamics of an open quantum
system arises is when this is coherently coupled to an auxiliary system
in contact with a Markovian bath. In such cases, while the joint dynamics of
- is Markovian and obeys a standard (bipartite) Lindblad-type master
equation (ME), this is in general not true for the reduced dynamics of .
Furthermore, there are several instances (\eg the dissipative Jaynes-Cummings
model) in which a {\it closed} ME for the 's state {\it cannot} even be
worked out. Here, we find a class of bipartite Lindblad-type MEs such that the
reduced ME of can be derived exactly and in a closed form for any initial
product state of -. We provide a detailed microscopic derivation of our
result in terms of a mapping between two collision modelsComment: 9 pages, 1 figur
Quantification of Order in the Lennard-Jones System
We conduct a numerical investigation of structural order in the shifted-force
Lennard-Jones system by calculating metrics of translational and
bond-orientational order along various paths in the phase diagram covering
equilibrium solid, liquid, and vapor states. A series of non-equilibrium
configurations generated through isochoric quenches, isothermal compressions,
and energy minimizations are also considered. Simulation results are analyzed
using an ordering map representation [Torquato et al., Phys. Rev. Lett. 84,
2064 (2000); Truskett et al., Phys. Rev. E 62, 993 (2000)] that assigns to both
equilibrium and non-equilibrium states coordinates in an order metric plane.
Our results show that bond-orientational order and translational order are not
independent for simple spherically symmetric systems at equilibrium. We also
demonstrate quantitatively that the Lennard-Jones and hard sphere systems
sample the same configuration space at supercritical densities. Finally, we
relate the structural order found in fast-quenched and minimum-energy
configurations (inherent structures).Comment: 35 pages, 8 figure
Positive or negative voting premium: what happened to private benefits in Italy?
A large body of research deals with voting premium as a proxy of private benefit of control. Almost all of them find positive voting premium, in particular in Italy. Therefore appears interesting to ask what is the current status of private benefits of control in Italy in the last decade (2007-2017). Surprisingly, we show three major findings: i) reduction of non-voting share in the Italian scenario; ii) prevalence of negative voting rights premium more than positive ones, thus conflicting with the assumption and the observations by other researchers; iii) limits of the voting premium method. Our aim is that this study, despite its limitations, may encourage further researches focused on the analysis of the improvement and the change in the Italian corporate governance. The article points out that interesting evidence already exists, although still much remains to do in the future
Quantum non-Markovian piecewise dynamics from collision models
Recently, a large class of quantum non-Markovian piecewise dynamics for an
open quantum system obeying closed evolution equations has been introduced [B.
Vacchini, Phys. Rev. Lett. 117, 230401 (2016)]. These dynamics have been
defined in terms of a waiting-time distribution between quantum jumps, along
with quantum maps describing the effect of jumps and the system's evolution
between them. Here, we present a quantum collision model with memory, whose
reduced dynamics in the continuous-time limit reproduces the above class of
non-Markovian piecewise dynamics, thus providing an explicit microscopic
realization.Comment: 18 pages, 1 figures. Submitted to "Open Systems and Information
Dynamics" as a contribution to the upcoming special issue titled "40 years of
the GKLS equation
Black brane solutions and their solitonic extremal limit in Einstein-scalar gravity
We investigate static, planar, solutions of Einstein-scalar gravity admitting
an anti-de Sitter (AdS) vacuum. When the squared mass of the scalar field is
positive and the scalar potential can be derived from a superpotential, minimum
energy theorems indicate the existence of a scalar soliton. On the other hand,
for these models, no-hair theorems forbid the existence of hairy black brane
solutions with AdS asymptotics. By considering a specific example (an exact
integrable model which has the form of a Toda molecule) and by deriving
explicit exact solution, we show that these models allow for hairy black brane
solutions with non-AdS domain wall asymptotics, whose extremal limit is a
scalar soliton. The soliton smoothly interpolates between a non-AdS domain wall
solution at and an AdS solution near .Comment: 5 pages, no figure
Quantum Critical Scaling under Periodic Driving
Universality is key to the theory of phase transition stating that the
equilibrium properties of observables near a phase transition can be classified
according to few critical exponents. These exponents rule an universal scaling
behaviour that witnesses the irrelevance of the model's microscopic details at
criticality. Here we discuss the persistence of such a scaling in a
one-dimensional quantum Ising model under sinusoidal modulation in time of its
transverse magnetic field. We show that scaling of various quantities
(concurrence, entanglement entropy, magnetic and fidelity susceptibility)
endures up to a stroboscopic time , proportional to the size of the
system. This behaviour is explained by noticing that the low-energy modes,
responsible for the scaling properties, are resilient to the absorption of
energy. Our results suggest that relevant features of the universality do hold
also when the system is brought out-of-equilibrium by a periodic driving.Comment: 11 pages, 7 figure
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