188 research outputs found
Exploring the framework of assemblage moment matrices and its applications in device-independent characterizations
In a recent work [Phys. Rev. Lett. 116, 240401 (2016)], a framework known by
the name of "assemblage moment matrices" (AMMs) has been introduced for the
device-independent quantification of quantum steerability and measurement
incompatibility. In other words, even with no assumption made on the
preparation device nor the measurement devices, one can make use of this
framework to certify, directly from the observed data, the aforementioned
quantum features. Here, we further explore the framework of AMM and provide
improved device-independent bounds on the generalized robustness of
entanglement, the incompatibility robustness and the incompatibility weight. We
compare the tightness of our device-independent bounds against those obtained
from other approaches. Along the way, we also provide an analytic form for the
generalized robustness of entanglement for an arbitrary two-qudit isotropic
state. When considering a Bell-type experiment in a tri- or more-partite
scenario, we further show that the framework of AMM provides a natural way to
characterize a superset to the set of quantum correlations, namely, one which
also allows post-quantum steering.Comment: 17 pages, 6 figures. Comments welcome
Boosting entanglement growth of many-body localization by superpositions of disorder
Many-body localization (MBL) can occur when strong disorders prevent an
interacting system from thermalization. To study the dynamics of such systems,
it is typically necessary to perform an ensemble average over many different
disorder configurations. Previous works have utilized an algorithm in which
different disorder profiles are mapped into a quantum ancilla. By preparing the
ancilla in a quantum superposition state, quantum parallelism can be harnessed
to obtain the ensemble average in a single computation run. In this work, we
modify this algorithm by performing a measurement on the ancilla. This enables
the determination of conditional dynamics not only by the ensemble average but
also by the quantum interference effect. Using a phenomenological analysis
based on local integrals of motion, we demonstrate that this protocol can lead
to an enhancement of the dephasing effect and a boost in the entanglement
growth for systems in the deep MBL phase. We also present numerical simulations
of the random XXZ model where this enhancement is also present in a smaller
disorder strength, beyond the deep MBL regime.Comment: 7 pages, 4 figure
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