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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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The finite-difference parquet method: Enhanced electron-paramagnon scattering opens a pseudogap.
Lihm JM, Kiese D, Lee SB, Kugler FB
- Year
- 2026
- Journal
- Proceedings of the National Academy of Sciences of the United States of America
- DOI
- 10.1073/pnas.2525308123
- arXiv
- -
We present the finite-difference parquet method that greatly improves the applicability and accuracy of two-particle correlation approaches to interacting electron systems. This method incorporates the nonperturbative local physics from a reference solution and builds all parquet diagrams while circumventing potentially divergent irreducible vertices. Its unbiased treatment of different fluctuations is crucial for reproducing the strong-coupling pseudogap in the underdoped Hubbard model, consistent with diagrammatic Monte Carlo calculations. We reveal a strong-coupling spin-fluctuation mechanism of the pseudogap with decisive vertex corrections that encode the enhanced, energy-dependent scattering amplitude between electrons and antiferromagnetic spin fluctuations.
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