Speaker: Arthur Parzygnat (MIT)
Title: Using quantum Bayes’ rule to infer the causal structure of quantum experiments
Abstract: The state of a quantum system at a given time is described by a density matrix. From the density matrix, one can calculate expectation values of measurements of observables. Is there an operator that encodes sequential measurements of a quantum system evolving from one time step to another? How is this operator different from a bipartite density operator? If one only has access to the expected values of the measurement outcomes, can we deduce whether those measurements occurred in succession or on two separate parts of a single bipartite system? Provocatively, can you tell whether there is an arrow of time based only on measurement statistics? How is the answer to this question different from what can be predicted assuming only classical probability? I will try to answer as many of these questions as time permits and in a way that is mostly accessible to those who learned introductory quantum physics.
This talk is based primarily on the papers https://arxiv.org/abs/2405.17555 (joint with James Fullwood) and https://arxiv.org/abs/2507.14278 (joint with Minjeong Song), along with earlier work establishing a quantum Bayes’ rule https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.4.020334 (joint with James Fullwood).
About: Weekly seminar of the Quantum Working Group, covering topics in quantum information theory and operator algebras. Contact Marius Junge (mjunge@illinois.edu), Felix Leditzky (leditzky@illinois.edu), or Amanda Young (ayoung86@illinois.edu) with questions or inquiries.