Optimization of a quantum tomography protocol for polarization qubits

Bogdanov, Yu. I.; Kulik, S. P.; Tikhonov, I. V.; Gavrichenko, A. K.

doi:10.1134/s0021364010120143

Cited by 41 publications

(52 citation statements)

References 8 publications

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“…However, the classical theorem by Hobart 12 and Derrick 13 poses severe restrictions on the type of nonlinear classical field theories that stabilizes 'particles'. A standard mechanism to evade these restrictions is operative in condensed-matter systems with a fixed 'handedness', i.e., systems without inversion symmetry 14 . In the long-wavelength limit, the handedness manifests in the form of Lifshitz invariants (linear gradient terms) 15 which favor a twisting of the order parameter along more than one spatial direction, thus allowing for localized modulations.…”

Section: Introductionmentioning

confidence: 99%

Kitaev anisotropy induces mesoscopicZ2vortex crystals in frustrated hexagonal antiferromagnets

et al. 2016

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The triangular-lattice Heisenberg antiferromagnet (HAF) is known to carry topological Z 2 vortex excitations which form a gas at finite temperatures. Here we show that the spin-orbit interaction, introduced via a Kitaev term in the exchange Hamiltonian, condenses these vortices into a triangular Z 2 vortex crystal at zero temperature. The cores of the Z 2 vortices show abrupt, soliton-like magnetization modulations and arise by a special intertwining of three honeycomb superstructures of ferromagnetic domains, one for each of the three sublattices of the 120• state of the pure HAF. This is a new example of a nucleation transition, analogous to the spontaneous formation of magnetic domains, Abrikosov vortices in type-II syperconductors, blue phases in cholesteric liquid crystals, and skyrmions in chiral helimagnets. As the mechanism relies on the interplay of geometric frustration and spin-orbital anisotropies, such vortex mesophases can materialize as a ground-state property in spin-orbit coupled correlated systems with nearly hexagonal topology, as in triangular or strongly frustrated honeycomb iridates.

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Section: Introductionmentioning

confidence: 99%

Kitaev anisotropy induces mesoscopicZ2vortex crystals in frustrated hexagonal antiferromagnets

et al. 2016

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“…4 (a), (b)) imply the attractive interaction between the skyrmions in the cone phase, whereas the axisymmetric skyrmions in the saturated state of chiral magnets (Fig. 4 (c)) have a repulsive interskyrmion potential 13,14,16 . e(ρ) has three characteristic radii R 1 , R 2 , and R 3 , dependence of which on the field is plotted in Fig.…”

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confidence: 99%

“…They exist as ensembles of weakly repulsive particles in the saturated phase of noncentrosymmetric magnets 4,13,14 in which all the atomic spins are parallel to an applied magnetic field. In cubic helimagnets, below a certain critical field, H D , the saturated phase transforms into the chiral helical state with the propagation direction along the applied field called the cone phase 2 .…”

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confidence: 99%

Three-dimensional chiral skyrmions with attractive interparticle interactions

Leonov

Monchesky

Loudon

et al. 2016

J. Phys.: Condens. Matter

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We introduce a new class of isolated three-dimensional skyrmion that can occur within the cone phase of chiral magnetic materials. These novel solitonic states consist of an axisymmetric core separated from the host phase by an asymmetric shell. These skyrmions attract one another. We derive regular solutions for isolated skyrmions arising in the cone phase of cubic helimagnets and investigate their bound states.PACS numbers: 75.30. Kz, 12.39.Dc, The Dzyaloshinskii-Moriya (DM) interaction in noncentrosymmetric magnets is a result of their crystallographic handedness 1 and is responsible for the formation of long-range modulations with a fixed sense of the magnetization rotation 1,2 and the stabilization of two-dimensional axisymmetric localized structures called skyrmions 3,4 . Long-range homochiral modulations (helices) were found in the noncentrosymmetric cubic ferromagnet MnSi several decades ago and since then, other cubic ferromagnets with B20 structures have been investigated intensively 5-7 as have other chiral magnetic materials 8,9 . Isolated chiral skyrmions have been discovered recently in PdFe/Ir(111) nanolayers with induced DM interactions and strong easy-axis anisotropy 10-12 .Chiral skyrmions are two-dimensional topological solitons with an axisymmetric structure localized in nanoscale cylindrical regions. They exist as ensembles of weakly repulsive particles in the saturated phase of noncentrosymmetric magnets 4,13,14 in which all the atomic spins are parallel to an applied magnetic field. In cubic helimagnets, below a certain critical field, H D , the saturated phase transforms into the chiral helical state with the propagation direction along the applied field called the cone phase 2 . Unlike the saturated phase, the boundary values imposed by the longitudinal modulations of the cone phase violate a rotational symmetry of the system, and are thus incompatible with the axisymmetric arrangement of skyrmions investigated in Refs. 4, 10, 11, and 13. Then, the question arises: "are there any localized states compatible with the encompassing cone phase?"In our report we address this compatibility problem and derive regular solutions for asymmetric skyrmions embedded into the cone phase. We demonstrate that unlike the repulsive axisymmetric skyrmions existing in the saturated states, chiral solitons in the cone phase have an attractive interskyrmion potential and form biskyrmion and multiskyrmion states.We consider the standard model for magnetic states in (color online). Magnetic structure of an isolated skyrmion in the cone phase: calculated contour plots of mz(x, y) in three layers with ∆ψc = 2π/3. Details of the magnetization distribution are given in Fig. 2. cubic non-centrosymmetric ferromagnets 1,2 ,where m = (sin θ cos ψ; sin θ sin ψ; cos θ) is the unity vector along the magnetization M, A is the exchange stiffness constant, D is the Dzyaloshinskii-Moriya (DM) coupling energy, and H is the applied magnetic field.Chiral modulations along the applied field with the period L D = 4πA/|D| correspon...

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“…From the point of view of the field theory, skyrmions are two-dimensional solitons known as an exception to the Hobart-Derrick theorem [7] due to the presence of Lifshitz invariants [8]. Due to their unusual transport properties, and compact size, which at some conditions can be reduced up to a few nano-meters [9] or even a few atomic distances [10], such types of chiral votices are considered as promising particle for information technology as well as an interesting object for fundamental research in nonlinear physics.…”

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confidence: 99%