10 research outputs found
Quantum realism: axiomatization and quantification
The emergence of an objective reality in line with the laws of the
microscopic world has been the focus of longstanding debates. Recent approaches
seem to have reached a consensus at least with respect to one aspect, namely,
that the encoding of information about a given observable in a physical degree
of freedom is a necessary condition for such observable to become an element of
the physical reality. Taking this as a fundamental premise and inspired by
quantum information theory, here we build an axiomatization for quantum realism
-- a notion of realism compatible with quantum theory. Our strategy consists of
listing some physically-motivated principles able to characterize quantum
realism in a ``metric'' independent manner. We introduce some criteria defining
monotones and measures of realism and then search for potential candidates
within some celebrated information theories -- those induced by the von
Neumann, R\'enyi, and Tsallis entropies. We explicitly construct some classes
of entropic quantifiers that are shown to satisfy (almost all of) the proposed
axioms and hence can be taken as faithful estimates for the degree of reality
(or definiteness) of a given physical observable. Hopefully, our framework may
offer a formal ground for further discussions on foundational aspects of
quantum mechanics.Comment: 15 pages, 4 figure
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
Nonlocality, quantum correlations, and violations of classical realism in the dynamics of two noninteracting quantum walkers
Semi-device independent nonlocality certification for near-term quantum networks
Verifying entanglement between parties is essential for creating a secure quantum network, and Bell tests are the most rigorous method for doing so. However, if there is any signaling between the parties, then the violation of these inequalities can no longer be used to draw conclusions about the presence of entanglement. This is because signaling between the parties allows them to coordinate their measurement settings and outcomes, which can give rise to a violation of Bell inequalities even if the parties are not genuinely entangled. There is a pressing need to examine the role of signaling in quantum communication protocols from multiple perspectives, including communication security, physics foundations, and resource utilization while also promoting innovative technological applications. Here, we propose a semi-device independent protocol that allows us to numerically correct for effects of correlations in experimental probability distributions, caused by statistical fluctuations and experimental imperfections. Our noise robust protocol presents a relaxation of a tomography-based optimisation method called the steering robustness, that uses semidefinite programming to numerically identify the optimal quantum steering inequality without the need for resource-intensive tomography. The proposed protocol is numerically and experimentally analyzed in the context of random, misaligned measurements, correcting for signalling where necessary, resulting in a higher probability of violation compared to existing state-of-the-art inequalities. Our work demonstrates the power of semidefinite programming for entanglement verification and brings quantum networks closer to practical applications