26 research outputs found
Superlattice switching from parametric instabilities in a driven-dissipative BEC in a cavity
We numerically obtain the full time-evolution of a parametrically-driven
dissipative Bose-Einstein condensate in an optical cavity and investigate the
implications of driving for the phase diagram. Beyond the normal and
superradiant phases, a third nonequilibrium phase emerges as a manybody
parametric resonance. This dynamical normal phase switches between two
symmetry-broken superradiant configurations. The switching implies a breakdown
of the system's mapping to the Dicke model. Unlike the other phases, the
dynamical normal phase shows features of nonintegrability and thermalization.Comment: 5 pages, 3 figure
Sensing Floquet-Majorana fermions via heat transfer
Time periodic modulations of the transverse field in the closed XY spin-1/2 chain generate a very rich dynamical phase diagram, with a hierarchy of Z_n topological phases characterized by differing numbers of Floquet-Majorana modes. This rich phase diagram survives when the system is coupled to dissipative end reservoirs. Circumventing the obstacle of preparing and measuring quasienergy configurations endemic to Floquet-Majorana detection schemes, we show that stroboscopic heat transport and spin density are robust observables to detect both the dynamical phase transitions and Majorana modes in dissipative settings. We find that the heat current provides very clear signatures of these Floquet topological phase transitions. In particular, we observe that the derivative of the heat current, with respect to a control parameter, changes sign at the boundaries separating topological phases with differing nonzero numbers of Floquet-Majorana modes. We present a simple scheme to directly count the number of Floquet-Majorana modes in a phase from the Fourier transform of the local spin density profile. Our results are valid provided the anisotropies are not strong and can be easily implemented in quantum engineered systems
Quench dynamics and scaling laws in topological nodal loop semimetals
We employ quench dynamics as an effective tool to probe different
universality classes of topological phase transitions. Specifically, we study a
model encompassing both Dirac-like and nodal loop criticalities. Examining the
Kibble-Zurek scaling of topological defect density, we discover that the
scaling exponent is reduced in the presence of extended nodal loop gap
closures. For a quench through a multicritical point, we also unveil a
path-dependent crossover between two sets of critical exponents. Bloch state
tomography finally reveals additional differences in the defect trajectories
for sudden quenches. While the Dirac transition permits a static trajectory
under specific initial conditions, we find that the underlying nodal loop leads
to complex time-dependent trajectories in general. In the presence of a nodal
loop, we find, generically, a mismatch between the momentum modes where
topological defects are generated and where dynamical quantum phase transitions
occur. We also find notable exceptions where this correspondence breaks down
completely.Comment: 8 pages, 7 figures; references adde
Quantum Metric Unveils Defect Freezing in Non-Hermitian Systems
Non-Hermiticity in quantum Hamiltonians leads to nonunitary time evolution
and possibly complex energy eigenvalues, which can lead to a rich phenomenology
with no Hermitian counterpart. In this work, we study the dynamics of an
exactly solvable non-Hermitian system, hosting both -symmetric
and -broken modes subject to a linear quench. Employing a fully
consistent framework, in which the Hilbert space is endowed with a nontrivial
dynamical metric, we analyze the dynamics of the generated defects. In contrast
to Hermitian systems, our study reveals that PT -broken time evolution leads to
defect freezing and hence the violation of adiabaticity. This physics
necessitates the so-called metric framework, as it is missed by the oft used
approach of normalizing quantities by the time-dependent norm of the state. Our
results are relevant for a wide class of experimental systems.Comment: Main text: 7 pages and 3 figure
Probing Chern number by opacity and topological phase transition by a nonlocal Chern marker
In 2D semiconductors and insulators, the Chern number of the valence band Bloch state is an important quantity that has been linked to various material properties, such as the topological order. We elaborate that the opacity of 2D materials to circularly polarized light over a wide range of frequencies, measured in units of the fine structure constant, can be used to extract a spectral function that frequency-integrates to the Chern number, offering a simple optical experiment to measure it. This method is subsequently generalized to finite temperature and locally on every lattice site by a linear response theory, which helps to extract the Chern marker that maps the Chern number to lattice sites. The long range response in our theory corresponds to a Chern correlator that acts like the internal fluctuation of the Chern marker, and is found to be enhanced in the topologically nontrivial phase. Finally, from the Fourier transform of the valence band Berry curvature, a nonlocal Chern marker is further introduced, whose decay length diverges at topological phase transitions and therefore serves as a faithful indicator of the transitions, and moreover can be interpreted as a Wannier state correlation function. The concepts discussed in this work explore multi-faceted aspects of topology and should help address the impact of system inhomogeneities