Causality in Pure Quantum Computation with Quantum Control
This paper proposes a typed lambda calculus with quantum control and its categorical semantics to study causality issues in quantum computation, extending pure quantum computation with higher-order functions and quantum conditional branching, and enforcing causality with a type system based on intuitionistic BV logic.
Proposed a new calculus and type system to study causality issues in quantum computation and enforce causality.
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Abstract
More Like ThisIndefinite causal order is a characteristic phenomenon in quantum computation, with examples including the quantum SWITCH and the OCB process. Not all such processes are believed to be physically realizable: while some implementations of the quantum SWITCH have been proposed, the OCB process is suspected to be unrealizable. This difference in realizability is commonly attributed to constraints imposed by physical causality. This paper studies such a causality issue in a higher-order setting, proposing a typed lambda calculus with quantum control and its categorical semantics. Our calculus extends pure quantum computation with higher-order functions and quantum conditional branching, and it is equipped with a type system based on intuitionistic BV logic to enforce causality. We also present a novel model that is closely related to the Caus construction, by which we prove that some physically-unrealizable processes are not definable in our language.