List of Publications
In quantum causality, local laboratories are typically assumed to be operationally independent, each free to choose its own reference frames. We ask whether such independence is compatible with nonclassical correlations, and address this question using the resource-theoretic framework. We formalize local gauge freedom on laboratory connections as a symmetry, and prove that any bipartite process covariant under this symmetry is causally separable. This result holds in arbitrary dimensions and applies both to marginals of multipartite quantum circuits and to general reductions across cuts. Because such covariance enforces a strict superselection rule, it explains why circuit-embeddable dynamics, such as the quantum switch, cannot violate bipartite causal inequalities, even asymptotically. Our analysis thus establishes that generating nonclassical causal correlations requires physical resources that break operational independence.
We demonstrate that the internal logical structure of a quantum circuit can leave a distinct thermodynamic signature under progressive decoherence. By comparing deep, conditionally branching circuits with shallow, uniform counterparts-while controlling for overall halting probability and physical resources-we show that branching architectures induce greater entropy flow into the environment. This effect is captured by a logical depth factor Ld, which quantifies entropy accumulation during environmental interactions. We validate our framework through detailed analysis of two 4-branch quantum circuits, demonstrating greater entropy production with Ld≈1.615 for conditional versus uniform architectures. An ancilla-based experimental protocol using controlled-phase gates provides a concrete pathway for detecting these thermodynamic signatures on current quantum platforms. Our results establish logical depth as a physically measurable quantity with implications for circuit design, compilation strategies, and verification protocols.
Reconstructions of quantum theory usually implicitly assume that experimental events are ordered within a global causal structure. The process matrix framework accommodates quantum correlations that violate an inequality verified by all causally ordered correlations. Using a generalized probabilistic framework, we propose three principles constraining bipartite correlations to the quantum bound. Our approach highlights the role of a measure of dependence other than mutual information for an information-theoretic reconstruction of causal structures in quantum theory.
Entanglement is defined between subsystems of a quantum system, and at fixed time two regions of space can be viewed as two subsystems of a relativistic quantum field. The entropy of entanglement between such subsystems is ill-defined unless an ultraviolet cutoff is introduced, but it still diverges in the continuum limit. This behaviour is generic for arbitrary finite-energy states, hence a conceptual tension with the finite entanglement entropy typical of nonrelativistic quantum systems. We introduce a novel approach to explain the transition from infinite to finite entanglement, based on coarse graining the spatial resolution of the detectors measuring the field state. We show that states with a finite number of particles become localized, allowing an identification between a region of space and the nonrelativistic degrees of freedom of the particles therein contained, and that the renormalized entropy of finite-energy states reduces to the entanglement entropy of nonrelativistic quantum mechanics.
In an experiment with both pre- and post-selection one can find a photon (the cat) in one place and its polarization (the smile) in another. Aharonov et al. asked recently whether more than two degrees of freedom could be separated in the same way. We show that this is possible and that the separation of properties from objects that carry them is in some situations even stronger.