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X-WR-CALDESC:InQubator for Quantum Simulation
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UID:MEC-69b09198d4248b8f24494f27a01367b9@iqus.uw.edu
DTSTART:20260224T213000Z
DTEND:20260224T223000Z
DTSTAMP:20260206T065600Z
CREATED:20260205
LAST-MODIFIED:20260215
PRIORITY:5
SEQUENCE:5
TRANSP:OPAQUE
SUMMARY:Quantum fields from quantum cellular automata: locality, interactions, and positive energy
DESCRIPTION:\nTodd Andrew Brun, University of Southern California\nQuantum cellular automata (QCAs) can be thought of as second-quantized versions of quantum walks on a lattice: local subsystems evolve unitarily while interacting with their neighbors. In the long-wavelength limit their solutions approach those of free quantum field theories, and can describe both bosons and fermions. QCAs with time-reversal symmetry will exhibit both positive and negative energy solutions, which are not distinguishable from each other in a finite region. This implies that a localized interaction between two QCAs will generally allow negative-energy solutions of the free theories to be excited, even if the initial state includes only positive-energy components, possibly leading to a cascade of particle pair creation. This coupling to negative-energy states cannot be eliminated for interactions with finite range; however, increasing the range of the interaction can make it possible to suppress this coupling exponentially, to the point where it is effectively zero. We show this in a model of a 1D fermionic QCA coupled to a 1D bosonic QCA, and discuss the implications for higher dimensions. (This work was done in collaboration with Leonard Mlodinow.)\n
URL:https://iqus.uw.edu/events/todd-brun-usc-17feb2026/
ORGANIZER;CN=Xiaojun Yao:MAILTO:xjyao@uw.edu
CATEGORIES:Seminars
LOCATION:C421 Physics and Astronomy Building
ATTACH;FMTTYPE=image/jpeg:https://iqus.uw.edu/wp-content/uploads/2026/02/Todd-Brun-1.jpg
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