arXiv subjects

Miguel Gallego

Publications and source records attributed to Miguel Gallego.

4 recordsLinked to original sources

arXiv2025

Quantum theory at the macroscopic scale

The quantum description of the microscopic world is incompatible with the classical description of the macroscopic world, both mathematically and conceptually. Nevertheless, it is generally accepted that classical mechanics emerges from quantum mechanics in the macroscopic limit. In this letter, we challenge this perspective and demonstrate that the behavior of a macroscopic system can retain all aspects of the quantum formalism, in a way that is robust against decoherence, particle losses and coarse-grained (imprecise) measurements. This departure from the expected classical description of macroscopic systems is not merely mathematical but also conceptual, as we show by the explicit violation of a Bell inequality and a Leggett-Garg inequality.

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arXiv2025

Robust and Indestructible Macroscopic Entanglement

In this letter we investigate the possibility of observing macroscopic entanglement, considering realistic factors such as decoherence, particle losses, and measurements of limited precision (coarse-grained collective measurements). This forms the foundation for an operational definition of robust macroscopic entanglement. We also propose an even more resilient concept of macroscopic entanglement, allowing the parties to randomly select their portion of the shared system. Through a straightforward example, we demonstrate that achieving this is feasible using a simple class of quantum states. Our result opens a path for generalizing notions of quantum entanglement, such as a genuine multipartite entanglement in the macroscopic domain.

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arXiv2024

Hilbert space separability and the Einstein-Podolsky-Rosen state

Quantum mechanics is formulated on a Hilbert space that is assumed to be separable. However, there seems to be no clear reason justifying this assumption. Does it have physical implications? We answer in the positive by proposing a test that witnesses the non-separability of the Hilbert space, at the expense of requiring measurements with uncountably many outcomes. In the search for a less elusive manifestation of non-separability, we consider the original Einstein-Podolsky-Rosen (EPR) state as a candidate for possessing nonlocal correlations stronger than any state in a separable Hilbert space. Nevertheless, we show that, under mild assumptions, this state is not a vector in any bipartite space, even non-separable, and therefore cannot be described within the standard Hilbert space formalism.

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arXiv2021

Macroscopically nonlocal quantum correlations

It is usually believed that coarse-graining of quantum correlations leads to classical correlations in the macroscopic limit. Such a principle, known as macroscopic locality, has been proved for correlations arising from independent and identically distributed (IID) entangled pairs. In this letter we consider the generic (non-IID) scenario. We find that the Hilbert space structure of quantum theory can be preserved in the macroscopic limit. This leads directly to a Bell violation for coarse-grained collective measurements, thus breaking the principle of macroscopic locality.

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