Fundamental Limits for Realizing Quantum Processes in Spacetime

Area of Science:

• Theoretical Physics
• Quantum Information
• Relativity

Background:

• Reconciling quantum mechanics and general relativity is a major challenge in physics.
• Causality is a fundamental concept that differs between quantum and relativistic theories.
• Bell's no-go theorem established limits on classical processes due to relativistic causality.

Purpose of the Study:

• To investigate fundamental limits on quantum processes within classical relativistic spacetimes.
• To explore the implications of indefinite causal order (ICO) for quantum causality.
• To reconcile quantum and relativistic notions of causality, particularly for quantum switch experiments.

Main Methods:

• Derivation of no-go theorems for quantum experiments in classical background spacetimes.
• Analysis of general quantum processes, including those with indefinite causal order (ICO).
• Examination of spacetime localization requirements for ICO processes respecting relativistic causality.

Main Results:

• No-go theorems demonstrate fundamental limits on quantum processes in classical spacetimes.
• Realizing ICO processes without violating relativistic causality necessitates non-localization of quantum systems.
• Any such ICO realization can be described by a more fundamental, definite, and acyclic causal order process.

Conclusions:

• The study provides a framework for reconciling quantum and relativistic causality.
• No-go results offer insights into the behavior of causality and information processing in quantum relativistic regimes.
• Findings are applicable to experimental realizations of quantum switch and other ICO processes.