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Paper 1
On the Necessity of Entanglement for the Explanation of Quantum Speedup
Michael E. Cuffaro
- Year
- 2011
- Journal
- arXiv preprint
- DOI
- arXiv:1112.1347
- arXiv
- 1112.1347
In this paper I argue that entanglement is a necessary component for any explanation of quantum speedup and I address some purported counter-examples that some claim show that the contrary is true. In particular, I address Biham et al.'s mixed-state version of the Deutsch-Jozsa algorithm, and Knill & Laflamme's deterministic quantum computation with one qubit (DQC1) model of quantum computation. I argue that these examples do not demonstrate that entanglement is unnecessary for the explanation of quantum speedup, but that they rather illuminate and clarify the role that entanglement does play.
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Non-Hermitian spectral flows and Berry-Chern monopoles
Lucien Jezequel, Pierre Delplace
- Year
- 2022
- Journal
- arXiv preprint
- DOI
- arXiv:2209.03876
- arXiv
- 2209.03876
We propose a non-Hermitian generalization of the correspondence between the spectral flow and the topological charges of band crossing points (Berry-Chern monopoles). A class of non-Hermitian Hamiltonians that display a complex-valued spectral flow is built by deforming an Hermitian model while preserving its analytical index. We relate those spectral flows to a generalized Chern number that we show to be equal to that of the Hermitian case, provided a line gap exists. We demonstrate the homotopic invariance of both the non-Hermitian Chern number and the spectral flow index, making explicit their topological nature. In the absence of a line gap, our system still displays a spectral flow whose topology can be captured by exploiting an emergent pseudo-Hermitian symmetry.
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