52 research outputs found
Lindblad non-universality of measurement phases and phase transitions
Entanglement phase transitions in hybrid quantum circuits are generally
argued to be properties of the individual trajectories rather than
measurement-averaged dynamics, despite the fact that results of measurements
are not used for feedback in the steady state. Here, we explicitly demonstrate
this difference by constructing a family of hybrid quantum circuits with
identical measurement-averaged dynamics that give different phases and phase
transitions. We propose measurement-averaged destruction of Bell state
entanglement as a proxy for determining which hybrid circuit yields the
lowest-entanglement dynamics and show that it holds numerically for the
measurements we consider. We comment on implications for quantum computing and
noisy quantum circuits
Dynamic trapping near a quantum critical point
The study of dynamics in closed quantum systems has recently been revitalized
by the emergence of experimental systems that are well-isolated from their
environment. In this paper, we consider the closed-system dynamics of an
archetypal model: spins near a second order quantum critical point, which are
traditionally described by the Kibble-Zurek mechanism. Imbuing the driving
field with Newtonian dynamics, we find that the full closed system exhibits a
robust new phenomenon -- dynamic critical trapping -- in which the system is
self-trapped near the critical point due to efficient absorption of field
kinetic energy by heating the quantum spins. We quantify limits in which this
phenomenon can be observed and generalize these results by developing a
Kibble-Zurek scaling theory that incorporates the dynamic field. Our findings
can potentially be interesting in the context of early universe physics, where
the role of the driving field is played by the inflaton or a modulus.Comment: 4 pages, 3 figures + 5 page supplemen
Enabling Adiabatic Passages Between Disjoint Regions in Parameter Space through Topological Transitions
We explore topological transitions in parameter space in order to enable
adiabatic passages between regions adiabatically disconnected within a given
parameter manifold. To this end, we study the Hamiltonian of two coupled qubits
interacting with external magnetic fields, and make use of the analogy between
the Berry curvature and magnetic fields in parameter space, with spectrum
degeneracies associated to magnetic charges. Symmetry-breaking terms induce
sharp topological transitions on these charge distributions, and we show how
one can exploit this effect to bypass crossing degeneracies. We also
investigate the curl of the Berry curvature, an interesting but as of yet not
fully explored object, which together with its divergence uniquely defines this
field. Finally, we suggest a simple method for measuring the Berry curvature,
thereby showing how one can experimentally verify our results.Comment: 17 pages, 11 figure
Strong-Disorder Renormalization Group for Periodically Driven Systems
Quenched randomness can lead to robust non-equilibrium phases of matter in
periodically driven (Floquet) systems. Analyzing transitions between such
dynamical phases requires a method capable of treating the twin complexities of
disorder and discrete time-translation symmetry. We introduce a real-space
renormalization group approach, asymptotically exact in the strong-disorder
limit, and exemplify its use on the periodically driven interacting quantum
Ising model. We analyze the universal physics near the critical lines and
multicritical point of this model, and demonstrate the robustness of our
results to the inclusion of weak interactions.Comment: 11 pages, 6 figures; published versio
Absence of Thermalization in Finite Isolated Interacting Floquet Systems
Conventional wisdom suggests that the long time behavior of isolated
interacting periodically driven (Floquet) systems is a featureless maximal
entropy state characterized by an infinite temperature. Efforts to thwart this
uninteresting fixed point include adding sufficient disorder to realize a
Floquet many-body localized phase or working in a narrow region of drive
frequencies to achieve glassy non-thermal behavior at long time. Here we show
that in clean systems the Floquet eigenstates can exhibit non-thermal behavior
due to finite system size. We consider a one-dimensional system of spinless
fermions with nearest-neighbor interactions where the interaction term is
driven. Interestingly, even with no static component of the interaction, the
quasienergy spectrum contains gaps and a significant fraction of the Floquet
eigenstates, at all quasienergies, have non-thermal average doublon densities.
We show that this non-thermal behavior arises due to emergent integrability at
large interaction strength and discuss how the integrability breaks down with
power-law dependence on system size.Comment: 10+8 pages, 13 figure
- …