71 research outputs found
Dynamical Topological Quantum Phase Transitions for Mixed States
We introduce and study dynamical probes of band structure topology in the
post-quench time-evolution from mixed initial states of quantum many-body
systems. Our construction generalizes the notion of dynamical quantum phase
transitions (DQPTs), a real-time counterpart of conventional equilibrium phase
transitions in quantum dynamics, to finite temperatures and generalized Gibbs
ensembles. The non-analytical signatures hallmarking these mixed state DQPTs
are found to be characterized by observable phase singularities manifesting in
the dynamical formation of vortex-antivortex pairs in the interferometric phase
of the density matrix. Studying quenches in Chern insulators, we find that
changes in the topological properties of the Hamiltonian can be identified in
this scenario, without ever preparing a topologically non-trivial or
low-temperature initial state. Our observations are of immediate relevance for
current experiments aimed at realizing topological phases in ultracold atomic
gases.Comment: 4 pages, 3 figures, version close to publishe
Coupled Atomic Wires in a Synthetic Magnetic Field
We propose and study systems of coupled atomic wires in a perpendicular
synthetic magnetic field as a platform to realize exotic phases of quantum
matter. This includes (fractional) quantum Hall states in arrays of many wires
inspired by the pioneering work [Kane et al. PRL {\bf{88}}, 036401 (2002)], as
well as Meissner phases and Vortex phases in double-wires. With one continuous
and one discrete spatial dimension, the proposed setup naturally complements
recently realized discrete counterparts, i.e. the Harper-Hofstadter model and
the two leg flux ladder, respectively. We present both an in-depth theoretical
study and a detailed experimental proposal to make the unique properties of the
semi-continuous Harper-Hofstadter model accessible with cold atom experiments.
For the minimal setup of a double-wire, we explore how a sub-wavelength spacing
of the wires can be implemented. This construction increases the relevant
energy scales by at least an order of magnitude compared to ordinary optical
lattices, thus rendering subtle many-body phenomena such as Lifshitz
transitions in Fermi gases observable in an experimentally realistic parameter
regime. For arrays of many wires, we discuss the emergence of Chern bands with
readily tunable flatness of the dispersion and show how fractional quantum Hall
states can be stabilized in such systems. Using for the creation of optical
potentials Laguerre-Gauss beams that carry orbital angular momentum, we detail
how the coupled atomic wire setups can be realized in non-planar geometries
such as cylinders, discs, and tori
Nonlocal annihilation of Weyl fermions in correlated systems
Weyl semimetals (WSMs) are characterized by topologically stable pairs of nodal points in the band structure that typically originate from splitting a degenerate Dirac point by breaking symmetries such as time-reversal or inversion symmetry. Within the independent-electron approximation, the transition between an insulating state and a WSM requires the local creation or annihilation of one or several pairs of Weyl nodes in reciprocal space. Here, we show that strong electron-electron interactions may qualitatively change this scenario. In particular, we reveal that the transition to a Weyl semimetallic phase can become discontinuous, and, quite remarkably, pairs of Weyl nodes with a finite distance in momentum space suddenly appear or disappear in the spectral function. We associate this behavior with the buildup of strong many-body correlations in the topologically nontrivial regions, manifesting in dynamical fluctuations in the orbital channel. We also highlight the impact of electronic correlations on the Fermi arcs
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A higher-resolution version of the Max Planck Institute Earth System Model (MPI-ESM1.2-HR)
The MPIâESM1.2 is the latest version of the Max Planck Institute Earth System Model and is the baseline for the Coupled Model Intercomparison Project Phase 6 and current seasonal and decadal climate predictions. This paper evaluates a coupled higherâresolution version (MPIâESM1.2âHR) in comparison with its lowerâresolved version (MPIâESM1.2âLR). We focus on basic oceanic and atmospheric mean states and selected modes of variability, the El Niño/Southern Oscillation and the North Atlantic Oscillation. The increase in atmospheric resolution in MPIâESM1.2âHR reduces the biases of upperâlevel zonal wind and atmospheric jet stream position in the northern extratropics. This results in a decrease of the storm track bias over the northern North Atlantic, for both winter and summer season. The blocking frequency over the European region is improved in summer, and North Atlantic Oscillation and related storm track variations improve in winter. Stable Atlantic meridional overturning circulations are found with magnitudes of ~16 Sv for MPIâESM1.2âHR and ~20 Sv for MPIâESM1.2âLR at 26°N. A strong sea surface temperature bias of ~5°C along with a too zonal North Atlantic current is present in both versions. The sea surface temperature bias in the eastern tropical Atlantic is reduced by ~1°C due to higherâresolved orography in MPIâESMâHR, and the region of the coldâtongue bias is reduced in the tropical Pacific. MPIâESM1.2âHR has a wellâbalanced radiation budget and its climate sensitivity is explicitly tuned to 3 K. Although the obtained reductions in longâstanding biases are modest, the improvements in atmospheric dynamics make this model well suited for prediction and impact studies
~Green's function topology of Majorana wires
We represent the ~topological invariant characterizing a one
dimensional topological superconductor using a Wess-Zumino-Witten dimensional
extension. The invariant is formulated in terms of the single particle Green's
function which allows to classify interacting systems. Employing a recently
proposed generalized Berry curvature method, the topological invariant is
represented independent of the extra dimension requiring only the single
particle Green's function at zero frequency of the interacting system.
Furthermore, a modified twisted boundary conditions approach is used to
rigorously define the topological invariant for disordered interacting systems.Comment: final versio
Global warming shifts the composition of the abundant bacterial phyllosphere microbiota as indicated by a cultivation dependent and independent study of the grassland phyllosphere of a long-term warming field-experiment
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Engineering and manipulating topological qubits in 1D quantum wires
We investigate the Josephson effect in TNT and NTN junctions, consisting of
topological (T) and normal (N) phases of semiconductor-superconductor 1D
heterostructures in the presence of a Zeeman field. A key feature of our setup
is that, in addition to the variation of the phase of the superconducting order
parameter, we allow the orientation of the magnetic field to change along the
junction. We find a novel magnetic contribution to the Majorana Josephson
coupling that permits the Josephson current to be tuned by changing the
orientation of the magnetic field along the junction. We also predict that a
spin current can be generated by a finite superconducting phase difference,
rendering these materials potential candidates for spintronic applications.
Finally, this new type of coupling not only constitutes a unique fingerprint
for the existence of Majorana bound states but also provides an alternative
pathway for manipulating and braiding topological qubits in networks of wires.Comment: references and a note were added in v2; 6 pages, 2 figures; v1 had
been submitted for the ICM2012 proceedings on the 31st of May 201
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