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arXiv · 2305.15649

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

Zhian Jia·Dagomir Kaszlikowski
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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.

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Zhian Jia, Dagomir Kaszlikowski. 2023-05-25. The spatiotemporal doubled density operator: a unified framework for analyzing spatial and temporal quantum processes. https://doi.org/10.1002/qute.202400102

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