Is Purity Eternal?

TL;DR

This paper explores the constraints on the evolution of pure quantum states into mixed states, emphasizing that energy conservation and Lorentz covariance restrict such purity loss.

Contribution

It presents a novel argument that purity loss cannot occur without violating Lorentz covariance if energy is conserved.

Findings

Purity loss conflicts with Lorentz covariance under energy conservation.

Phenomenological restrictions limit pure-to-mixed state evolution.

Theoretical implications for quantum state evolution and symmetry principles.

Abstract

Phenomenological and formal restrictions on the evolution of pure into mixed states are discussed. In particular, it is argued that, if energy is conserved, loss of purity is incompatible with the weakest possible form of Lorentz covariance.