The spatiotemporal doubled density operator: a unified framework for analyzing spatial and temporal quantum processes

Abstract

The measurement statistics for spatial and temporal quantum processes are produced through distinct mechanisms. Measurements that are space-like separated exhibit non-signaling behavior. However, time-like separated measurements can only result in one-way non-signaling, as the past is independent of the future, but the opposite is not true. This work presents the doubled density operator as a comprehensive framework for studying quantum processes in space-time. It effectively captures all the physical information of the process, with the measurement and Born rule showing uniformity for both spatial and temporal cases. We demonstrate that the equal-time density operator can be derived by performing a partial trace operation on the doubled density operator. Furthermore, the temporality of the quantum process can be detected by conducting a partial trace operation on either the left or right half of the doubled density operator.

arXiv commentv1:7+7 pages, comments welcome

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Cited by in corpus (4)

• Quantum space-time marginal problem: global causal structure from local causal information
• Unification of spatiotemporal quantum formalisms: mapping between process and pseudo-density matrices via multiple-time states
• Quantum dynamics as a pseudo-density matrix
• Experimental Virtual Quantum Broadcasting