4 research outputs found
Fully non-positive-partial-transpose genuinely entangled subspaces
Genuinely entangled subspaces are a class of subspaces in the multipartite
Hilbert spaces that are composed of only genuinely entangled states. They are
thus an interesting object of study in the context of multipartite
entanglement. Here we provide a construction of multipartite subspaces that are
not only genuinely entangled but also fully non-positive-partial-transpose
(NPT) in the sense that any mixed state supported on them has non-positive
partial transpose across any bipartition. Our construction originates from the
stabilizer formalism known for its use in quantum error correction. To this
end, we first introduce a couple of criteria allowing to assess whether any
state from a given non-trivial stabilizer subspace is genuinely multipartite
entangled. We then use these criteria to construct genuinely entangled
stabilizer subspaces for any number of parties and arbitrary local dimension
and conjecture them to be of maximal dimension achievable within the stabilizer
formalism. At the same time, we prove that every genuinely entangled subspace
is fully NPT in the above sense, which implies a quite surprising fact that no
genuinely entangled stabilizer subspace can support PPT entangled states
Self-testing of any pure entangled state with minimal number of measurements and optimal randomness certification in one-sided device-independent scenario
Certification of quantum systems and their properties has become a field of
intensive studies. Here, taking advantage of the one-sided device-independent
scenario (known also as quantum steering scenario), we propose a self-testing
scheme for all bipartite entangled states using a single family of steering
inequalities with the minimal number of two measurements per party. Building on
this scheme we then show how to certify all rank-one extremal measurements,
including non-projective -outcome measurements, which in turn can be used
for certification of the maximal amount of randomness from every entangled
bipartite state of local dimension , that is, bits. Finally, in a
particular case of , we extend our self-testing results to the fully
device-independent setting.Comment: Corrected and improved version. Comments are welcome
High-dimensional monitoring and the emergence of realism via multiple observers
Quantum measurements are unitary evolutions followed by partial traces. Based
on that, we address the problem of the emergence of physical reality from the
quantum world by introducing a model that interpolates between weak and strong
non-selective measurements for qudits. Our model, which is based on generalized
observables and Heisenberg-Weyl operators, suggests that for high-dimensional
qudits, full information about the system can only be obtained by making the
system interact with not just one but several environmental qudits, following a
Quantum Darwinism framework.Comment: 12 pages, 2 figure