Composite particles with minimum uncertainty in spacetime

TL;DR

This paper introduces a new class of states with minimal space-time uncertainty that prevent delocalisation of composite particles, enabling their use in quantum and relativistic experiments.

Contribution

It proposes a novel theoretical framework that minimizes space-time uncertainty in composite particles, overcoming a key limitation in their coherence properties.

Findings

New states fully prevent delocalisation of composite particles

Uncertainty minimized between position and velocity, not position and momentum

Provides a theoretical tool for quantum-relativistic experiments with composite particles

Abstract

Composite particles---atoms, molecules, or microspheres---are unique tools for testing joint quantum and general relativistic effects, macroscopic limits of quantum mechanics, and searching for new physics. However, all studies of the free propagation of these particles find that they delocalise into separate internal energy components, destroying their spatial coherence. This renders them unsuitable for experimental applications, as well as theoretical studies where they are used as idealised test masses or clocks. Here we solve this problem by introducing a new class of states with minimal uncertainty in space-time that fully overcome the delocalisation. The relevant physics comes from minimising the uncertainty between position and velocity, rather than position and momentum, while directly accounting for mass as an operator. Our results clarify the nature of composite particles, providing a currently missing theoretical tool with direct relevance for studies of joint foundations of quantum and relativistic phenomena, which removes a roadblock that could limit near-future quantum tests using composite particles.