Broken symmetry in a correlated quantum control landscape
Files
Accepted manuscript
Date
2018-05-15
Authors
Bukov, Marin Georgiev
Day, Alexandre G.R.
Weinberg, Phillip
Polkovnikov, Anatoli
Mehta, Pankaj
Sels, Dries
Version
Accepted manuscript
OA Version
Citation
Marin Bukov, Alexandre GR Day, Phillip Weinberg, Anatoli Polkovnikov, Pankaj Mehta, Dries Sels. 2018. "Broken Symmetry in a Correlated Quantum Control Landscape." Physical Review A, Volume 97, pp. 052114 - 052114. https://doi.org/10.1103/PhysRevA.97.052114
Abstract
We analyze the physics of optimal protocols to prepare a target state with high fidelity in a symmetrically coupled two-qubit system. By varying the protocol duration, we find a discontinuous phase transition, which is characterized by a spontaneous breaking of a Z2 symmetry in the functional form of the optimal protocol, and occurs below the quantum speed limit. We study in detail this phase and demonstrate that even though high-fidelity protocols come degenerate with respect to their fidelity, they lead to final states of different entanglement entropy shared between the qubits. Consequently, while globally both optimal protocols are equally far away from the target state, one is locally closer than the other. An approximate variational mean-field theory which captures the physics of the different phases is developed.