Abstract
Projective measurement, a basic operation in quantum mechanics, can induce seemingly nonlocal effects. In this work, we analyze such effects in many-body systems by studying the nonequilibrium dynamics of weakly monitored quantum circuits, focusing on entanglement generation and information spreading. We find that, due to measurements, the entanglement dynamics in monitored circuits is indeed “faster” than that of unitary ones in several ways. Specifically, we find that a pair of well-separated regions can become entangled in a time scale , sublinear in their distance . For the case of Clifford monitored circuits, this originates from superballistically growing stabilizer generators of the evolving state. In addition, we find initially local information can spread superlinearly as . Furthermore, by viewing the dynamics as a dynamical encoding process, we show that the superlinear growing length scale relates to an encoding time that is sublinear in system size. To quantify the information dynamics, we develop a formalism generalizing operator spreading to nonunitary dynamics, which is of independent interest.
- Received 12 May 2023
- Accepted 31 October 2023
DOI:https://doi.org/10.1103/PRXQuantum.4.040332
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Many peculiar features of quantum mechanics involve projective measurements. For instance, by using entangled particles as a resource, quantum measurements enable the teleportation of quantum information between parties that have never previously interacted. This type of measurement-induced quantum nonlocality underpins many applications in quantum information.
We investigate the role of this effect in scenarios where many quantum degrees of freedom interact, while measurements are performed infrequently on each component of the system. We observe that both quantum entanglement and quantum correlation spread superlinearly with time as a consequence of microscopic quantum teleportation events that occur intermittently. Our findings reveal a marked difference between many-body quantum dynamics with and without measurements; in the latter case, it is well known that correlation or information cannot propagate faster than a constant speed limit.
