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Paper 1
Robustness of QMA against witness noise
Friederike Anna Dziemba
- Year
- 2016
- Journal
- arXiv preprint
- DOI
- arXiv:1611.07332
- arXiv
- 1611.07332
Using the tool of concatenated stabilizer coding, we prove that the complexity class QMA remains unchanged even if every witness qubit is disturbed by constant noise. This result may not only be relevant for physical implementations of verifying protocols but also attacking the relationship between the complexity classes QMA, QCMA and BQP, which can be reformulated in this unified framework of a verifying protocol receiving a disturbed witness. While QCMA and BQP are described by fully dephasing and depolarizing channels on the witness qubits, respectively, our result proves QMA to be robust against 27% dephasing and 18% depolarizing noise.
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Superradiance and subradiance in extended media
Jonathan F. Schonfeld
- Year
- 2017
- Journal
- arXiv preprint
- DOI
- arXiv:1707.05237
- arXiv
- 1707.05237
In super- or subradiance, a quantum superposition of excited atoms collectively emits a photon much more or much less rapidly than an isolated atom. Superradiant and subradiant lifetimes have been derived for finite spheres of uniform media, either by simulating random samples or by expanding in spherical harmonics and analyzing Bessel functions. We introduce a simple regulator that applies to unbounded media, enabling trivial derivation and analysis of lifetimes via elementary Fourier techniques. The regulator can be interpreted as a correlation length for atomic positions; the regularized system describes localized regions of enhanced radiative activity in otherwise quiescent surroundings.
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