1,169 research outputs found
Topological Heat Transport and Symmetry-Protected Boson Currents
The study of non-equilibrium properties in topological systems is of
practical and fundamental importance. Here, we analyze the stationary
properties of a two-dimensional bosonic Hofstadter lattice coupled to two
thermal baths in the quantum open-system formalism. Novel phenomena appear like
chiral edge heat currents that are the out-of-equilibrium counterparts of the
zero-temperature edge currents. They support a new concept of dissipative
symmetry-protection, where a set of discrete symmetries protects topological
heat currents, differing from the symmetry-protection devised in closed systems
and zero-temperature. Remarkably, one of these currents flows opposite to the
decreasing external temperature gradient. As the starting point, we consider
the case of a single external reservoir already showing prominent results like
thermal erasure effects and topological thermal currents. Our results are
experimentally accessible with platforms like photonics systems and optical
lattices.Comment: RevTeX4 file, color figure
Symmetry-protected Topological Phases at Finite Temperature
We have applied the recently developed theory of topological Uhlmann numbers
to a representative model of a topological insulator in two dimensions, the
Qi-Wu-Zhang model. We have found a stable symmetry-protected topological (SPT)
phase under external thermal fluctuations in two-dimensions. A complete phase
diagram for this model is computed as a function of temperature and coupling
constants in the original Hamiltonian. It shows the appearance of large stable
phases of matter with topological properties compatible with thermal
fluctuations or external noise and the existence of critical lines separating
abruptly trivial phases from topological phases. These novel critical
temperatures represent thermal topological phase transitions. The initial part
of the paper comprises a self-contained explanation of the Uhlmann geometric
phase needed to understand the topological properties that it may acquire when
applied to topological insulators and superconductors.Comment: Contribution to the focus issue on "Artificial Graphene". Edited by
Maciej Lewenstein, Vittorio Pellegrini, Marco Polini and Mordechai (Moti)
Sege
The dynamical equation of the spinning electron
We obtain by invariance arguments the relativistic and non-relativistic
invariant dynamical equations of a classical model of a spinning electron. We
apply the formalism to a particular classical model which satisfies Dirac's
equation when quantised. It is shown that the dynamics can be described in
terms of the evolution of the point charge which satisfies a fourth order
differential equation or, alternatively, as a system of second order
differential equations by describing the evolution of both the center of mass
and center of charge of the particle. As an application of the found dynamical
equations, the Coulomb interaction between two spinning electrons is
considered. We find from the classical viewpoint that these spinning electrons
can form bound states under suitable initial conditions. Since the classical
Coulomb interaction of two spinless point electrons does not allow for the
existence of bound states, it is the spin structure that gives rise to new
physical phenomena not described in the spinless case. Perhaps the paper may be
interesting from the mathematical point of view but not from the point of view
of physics.Comment: Latex2e, 14 pages, 5 figure
Observation of topological Uhlmann phases with superconducting qubits
Topological insulators and superconductors at finite temperature can be
characterized by the topological Uhlmann phase. However, a direct experimental
measurement of this invariant has remained elusive in condensed matter systems.
Here, we report a measurement of the topological Uhlmann phase for a
topological insulator simulated by a system of entangled qubits in the IBM
Quantum Experience platform. By making use of ancilla states, otherwise
unobservable phases carrying topological information about the system become
accessible, enabling the experimental determination of a complete phase diagram
including environmental effects. We employ a state-independent measurement
protocol which does not involve prior knowledge of the system state. The
proposed measurement scheme is extensible to interacting particles and
topological models with a large number of bands.Comment: RevTex4 file, color figure
Reactivity of dolomitizing fluids and Mg source evaluation of fault-controlled dolomitization at the Benicàssim outcrop analogue (Maestrat Basin, E Spain)
Peer reviewedPostprin
Robust nonequilibrium edge currents with and without band topology
We study two-dimensional bosonic and fermionic lattice systems under
nonequilibrium conditions corresponding to a sharp gradient of temperature
imposed by two thermal baths. In particular, we consider a lattice model with
broken time-reversal symmetry that exhibits both topologically trivial and
nontrivial phases. Using a nonperturbative approach, we characterize the
nonequilibrium current distribution in different parameter regimes. For both
bosonic and fermionic systems weakly coupled to the reservoirs, we find chiral
edge currents that are robust against defects on the boundary or in the bulk.
This robustness not only originates from topological effects at zero
temperature but, remarkably, also persists as a result of dissipative
symmetries in regimes where band topology plays no role. Chirality of the edge
currents implies that energy locally flows against the temperature gradient
without any external work input. In the fermionic case, there is also a regime
with topologically protected boundary currents, which nonetheless do not
circulate around all system edges.Comment: 5+4 pages, 4+2 figures. Comments welcom
Lower Cretaceous (Hauterivian-Albian) ammonite biostratigraphy in the Maestrat Basin (E Spain)
Peer reviewedPublisher PD
Quantum dynamics in photonic crystals
Employing a recently developed method that is numerically accurate within a
model space simulating the real-time dynamics of few-body systems interacting
with macroscopic environmental quantum fields, we analyze the full dynamics of
an atomic system coupled to a continuum light-field with a gapped spectral
density. This is a situation encountered, for example, in the radiation field
in a photonic crystal, whose analysis has been so far been confined to limiting
cases due to the lack of suitable numerical techniques. We show that both
atomic population and coherence dynamics can drastically deviate from the
results predicted when using the rotating wave approximation, particularly in
the strong coupling regime. Experimental conditions required to observe these
corrections are also discussed.Comment: 5 pages, 2 figures Updated with published versio
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