Tommaso Guaita

Feynman [1] remarked that the spin–statistics theorem is one of the few principles in physics that can be simply stated yet whose proof requires the full machinery of relativistic quantum field theory. A central implication of this theorem is that fermions cannot be composite bosons. This naturally raises the question: can this fact admit an elementary, non-relativistic proof? Bell’s theorem [2] provides a paradigm for such elementary arguments: under the minimal assumption of causality, it rules out classical (local hidden-variable) explanations of quantum correlations. In particular, it shows that quantum systems such as qubits — carried, for instance, by bosons — cannot be simulated by classical bits, and that bosonic correlations cannot arise from compositions of classical particles. Inspired by this framework, we introduce a fermionic thought experiment whose outcome shows that fermions cannot be composite bosons through reasoning analogous to Bell’s theorem. The thought experiment is formulated in the setting of distributed quantum networks and draws on concepts from distributed computing. Within this framework, we prove the existence of fermionic correlations that admit no local hidden-qubit model and are strictly stronger than Bell nonlocal correlations achievable with qubits. This shows that standard quantum information theory is insufficient to represent information carried by indistinguishable fermions in distributed settings. The assumptions remain minimal: causality is preserved, and the distributed parties have no knowledge of the network topology. Our result therefore provides an information-theoretic, non-relativistic proof of the fundamental fermion–boson distinction implied by the spin–statistics theorem. References: [1] R. P. Feynman, The Character of Physical Law, MIT Press (1965). [2] J. S. Bell, “On the Einstein–Podolsky–Rosen paradox,” Physics (1964).

Quantum simulation is a central application of near-term quantum devices, pursued in both analog and digital architectures. A key challenge for both paradigms is the effect of imperfections and noise on predictive power. In this work, we present a rigorous and physically transparent comparison of the stability of digital and analog quantum simulators under a variety of perturbative noise models. We provide rigorous worst- and average-case error bounds for noisy quantum simulation of local observables. We find that the two paradigms show comparable scaling in the worst case, while exhibiting different forms of enhanced error cancellation on average. We further analyze Gaussian and Brownian noise processes, deriving concentration bounds that capture typical deviations beyond worst-case guarantees. These results provide a unified framework for quantifying the robustness of noisy quantum simulations and identify regimes where digital methods have intrinsic advantages and when we can see similar behavior.