||O L D N E W S
21.2.2018 Research publication
Incompatibility of unbiased qubit observables and Pauli channels
A quantum observable and a channel are considered compatible if they form parts of the same measurement device, otherwise they are incompatible. Constrains on compatibility between observables and channels can be quantified via relations highlighting the necessary tradeoffs between noise and disturbance within quantum measurements. In this paper we shall discuss the general properties of these compatibility relations and then fully characterize the compatibility conditions for an unbiased qubit observable and a Pauli channel. The implications of the characterization are demonstrated on some concrete examples.
Teiko Heinosaari, Daniel Reitzner, Tomáš Rybár, and Mário Ziman
Phys. Rev. A 97, 022112 (2018) | +++ |
APVV-14-0878 (QETWORK), VEGA 2/0130/15 (OAQS), SASPRO (0055/01/01)
Pilot School QUTEsk
9.1.2018 Research publication
Original electric-vertex formulation of the symmetric eight-vertex model on the square lattice is fully nonuniversal
The partition function of the symmetric (zero electric field) eight-vertex model on a square lattice can be formulated either in the original “electric” vertex format or in an equivalent “magnetic” Ising-spin format. In this paper, both electric and magnetic versions of the model are studied numerically by using the corner transfer matrix renormalization-group method which provides reliable data. The emphasis is put on the calculation of four specific critical exponents, related by two scaling relations, and of the central charge. The numerical method is first tested in the magnetic format, the obtained dependencies of critical exponents on the model's parameters agree with Baxter's exact solution, and weak universality is confirmed within the accuracy of the method due to the finite size of the system. In particular, the critical exponents η and δ are constant as required by weak universality. On the other hand, in the electric format, analytic formulas based on the scaling relations are derived for the critical exponents ηe and δe which agree with our numerical data. These exponents depend on the model's parameters which is evidence for the full nonuniversality of the symmetric eight-vertex model in the original electric formulation.
Roman Krčmár and Ladislav Šamaj
Phys. Rev. E 97, 012108 (2018) |+++|
APVV-16-0186 (EXSES), VEGA 2/0130/15 (OAQS),