Graduation Year


Date of Submission


Document Type

Open Access Senior Thesis


Best Senior Thesis in Physical Sciences

Degree Name

Bachelor of Arts



Reader 1

Dr. Kevin Setter

Reader 2

Dr. Adam Landsberg

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© 2023 Brian Lee


In the decoherence account of quantum mechanics, a choice of particular tensor product structure (a particular partition of system into subsystems) is assumed. We explore whether it is possible to relax this arbitrary choice by requiring that a valid tensor product structure admits a quasi-classical description. Such tensor product structures are said to be quasi-classical or decoherence-selected tensor product structures. This project generalizes a 2-qubit quasi-classical tensor product structure selection algorithm to an n-qubit selection algorithm, which allows us to, for the first time, consider the relationship between decoherence-selected tensor product structures and locality-selected tensor product structures. To generalize the algorithm, we make novel use of a local unitary equivalence check algorithm from [ 1]. For n-qubit systems in the infinite temperature limit, we find that there always exists an exact quasi-classical tensor product structure. We prove a theorem that characterizes all quasi-classical tensor product structures for any n-qubit system in the infinite temperature limit. We find that quasi-classical tensor product structures are precisely the tensor product structures generated by either non-interacting or diagonal Hamiltonians. We also find formulae for the mean and standard deviation of entanglement entropy growth within local unitary orbits of a tensor product structure, quantitatively showing that some tensor product structures are better than others.