Assignment maps for arbitrary reduced quantum dynamics
Abstract
Given an open quantum system S with environment E, we establish a one-to-one correspondence between completely positive trace-preserving (CPTP) maps from S to E and assignment maps initializing the composite system SE in a possibly correlated state prior to unitary evolution. We show that every possible joint state ρSE can be realized by such assignment maps, which are inherently Hermiticity-preserving and trace-preserving (HPTP). While these maps sacrifice global positivity, we derive a simple necessary and sufficient condition for any local state of S to belong to their domain of validity. Furthermore, we prove that the geometry of this domain is governed by the joint state assigned to the maximally mixed input, ensuring that a non-zero volume of admissible local states can readily coexist with initial system-environment entanglement. Finally, we provide an operational protocol for witnessing such limits of validity.
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BibTeX
@misc{fullwood2026assignment,
title = {{Assignment maps for arbitrary reduced quantum dynamics}},
author = {James Fullwood and Weixiang Ye},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27338},
eprint = {2610.27338},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27338},
}
RIS
TY - UNPB
TI - Assignment maps for arbitrary reduced quantum dynamics
AU - James Fullwood
AU - Weixiang Ye
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2610.27338
UR - https://arxiv.org/abs/2610.27338
AB - Given an open quantum system S with environment E, we establish a one-to-one correspondence between completely positive trace-preserving (CPTP) maps from S to E and assignment maps initializing the composite system SE in a possibly correlated state prior to unitary evolution. We show that every possible joint state ρ_SE can be realized by such assignment maps, which are inherently Hermiticity-preserving and trace-preserving (HPTP). While these maps sacrifice global positivity, we derive a simple necessary and sufficient condition for any local state of S to belong to their domain of validity. Furthermore, we prove that the geometry of this domain is governed by the joint state assigned to the maximally mixed input, ensuring that a non-zero volume of admissible local states can readily coexist with initial system-environment entanglement. Finally, we provide an operational protocol for witnessing such limits of validity.
ER -