5,193 research outputs found
Hall viscosity, orbital spin, and geometry: paired superfluids and quantum Hall systems
The Hall viscosity, a non-dissipative transport coefficient analogous to Hall
conductivity, is considered for quantum fluids in gapped or topological phases.
The relation to mean orbital spin per particle discovered in previous work by
one of us is elucidated with the help of examples, using the geometry of shear
transformations and rotations. For non-interacting particles in a magnetic
field, there are several ways to derive the result (even at non-zero
temperature), including standard linear response theory. Arguments for the
quantization, and the robustness of Hall viscosity to small changes in the
Hamiltonian that preserve rotational invariance, are given. Numerical
calculations of adiabatic transport are performed to check the predictions for
quantum Hall systems, with excellent agreement for trial states. The
coefficient of k^4 in the static structure factor is also considered, and shown
to be exactly related to the orbital spin and robust to perturbations in
rotation invariant systems also.Comment: v2: Now 30 pages, 10 figures; new calculation using disk geometry;
some other improvements; no change in result
From source to target and back: symmetric bi-directional adaptive GAN
The effectiveness of generative adversarial approaches in producing images
according to a specific style or visual domain has recently opened new
directions to solve the unsupervised domain adaptation problem. It has been
shown that source labeled images can be modified to mimic target samples making
it possible to train directly a classifier in the target domain, despite the
original lack of annotated data. Inverse mappings from the target to the source
domain have also been evaluated but only passing through adapted feature
spaces, thus without new image generation. In this paper we propose to better
exploit the potential of generative adversarial networks for adaptation by
introducing a novel symmetric mapping among domains. We jointly optimize
bi-directional image transformations combining them with target self-labeling.
Moreover we define a new class consistency loss that aligns the generators in
the two directions imposing to conserve the class identity of an image passing
through both domain mappings. A detailed qualitative and quantitative analysis
of the reconstructed images confirm the power of our approach. By integrating
the two domain specific classifiers obtained with our bi-directional network we
exceed previous state-of-the-art unsupervised adaptation results on four
different benchmark datasets
Topology by dissipation
Topological states of fermionic matter can be induced by means of a suitably
engineered dissipative dynamics. Dissipation then does not occur as a
perturbation, but rather as the main resource for many-body dynamics, providing
a targeted cooling into a topological phase starting from an arbitrary initial
state. We explore the concept of topological order in this setting, developing
and applying a general theoretical framework based on the system density matrix
which replaces the wave function appropriate for the discussion of Hamiltonian
ground-state physics. We identify key analogies and differences to the more
conventional Hamiltonian scenario. Differences mainly arise from the fact that
the properties of the spectrum and of the state of the system are not as
tightly related as in a Hamiltonian context. We provide a symmetry-based
topological classification of bulk steady states and identify the classes that
are achievable by means of quasi-local dissipative processes driving into
superfluid paired states. We also explore the fate of the bulk-edge
correspondence in the dissipative setting, and demonstrate the emergence of
Majorana edge modes. We illustrate our findings in one- and two-dimensional
models that are experimentally realistic in the context of cold atoms.Comment: 61 pages, 8 figure
Dynamical signatures of topological order in the driven-dissipative Kitaev chain
We investigate the effects of dissipation and driving on topological order in
superconducting nanowires. Rather than studying the non-equilibrium steady
state, we propose a method to classify and detect dynamical signatures of
topological order in open quantum systems. Bulk winding numbers for the
Lindblad generator of the dissipative Kitaev chain are
found to be linked to the presence of Majorana edge master modes -- localized
eigenmodes of . Despite decaying in time, these modes
provide dynamical fingerprints of the topological phases of the closed system,
which are now separated by intermediate regions where winding numbers are
ill-defined and the bulk-boundary correspondence breaks down. Combining these
techniques with the Floquet formalism reveals higher winding numbers and
different types of edge modes under periodic driving. Finally, we link the
presence of edge modes to a steady state current.Comment: Submission to SciPost. 29 pages, 8 figure
Sensitivity analysis of oscillator models in the space of phase-response curves: Oscillators as open systems
Oscillator models are central to the study of system properties such as
entrainment or synchronization. Due to their nonlinear nature, few
system-theoretic tools exist to analyze those models. The paper develops a
sensitivity analysis for phase-response curves, a fundamental one-dimensional
phase reduction of oscillator models. The proposed theoretical and numerical
analysis tools are illustrated on several system-theoretic questions and models
arising in the biology of cellular rhythms
Topological phases with parafermions: theory and blueprints
We concisely review the recent evolution in the study of parafermions --
exotic emergent excitations that generalize Majorana fermions and similarly
underpin a host of novel phenomena. First we illustrate the intimate connection
between Z_3-symmetric "spin" chains and one-dimensional parafermion lattice
models, highlighting how the latter host a topological phase featuring
protected edge zero modes. We then tour several blueprints for the laboratory
realization of parafermion zero modes -- focusing on quantum
Hall/superconductor hybrids, quantum Hall bilayers, and two-dimensional
topological insulators -- and describe striking experimental fingerprints that
they provide. Finally, we discuss how coupled parafermion arrays in quantum
Hall architectures yield topological phases that potentially furnish hardware
for a universal, intrinsically decoherence-free quantum computer.Comment: 14 pages, 4 figures; slated for Annual Reviews of Condensed Matter
Physic
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