Reversible quantum measurement with arbitrary spins

We propose a physically reversible quantum measurement of an arbitrary spin-s system using a spin-j probe via an Ising interaction. In the case of a spin-1/2 system (s=1/2), we explicitly construct a reversing measurement and evaluate the degree of reversibility in terms of fidelity. The recovery of the measured state is pronounced when the probe has a high spin (j>1/2), because the fidelity changes drastically during the reversible measurement and the reversing measurement. We also show that the reversing measurement scheme for a spin-1/2 system can serve as an experimentally feasible approximate reversing measurement for a high-spin system (s>1/2). If the interaction is sufficiently weak, the reversing measurement can recover a cat state almost deterministically in spite of there being a large fidelity change.Comment: 35 pages, 11 figures, Sec. 3.2 is adde

Diagnostics for the ground state phase of a spin-2 Bose-Einstein condensate

We propose a method to determine the singlet-pair energy of a spin-2 Bose-Einstein condensate (BEC). By preparing the initial populations in the magnetic sublevels 0, 2, -2 with appropriate relative phases, we can obtain the coefficient of the spin singlet-pair term from the spin exchange dynamics. This method is suitable for hyperfine states with short lifetimes, since only the initial change in the population of each magnetic sublevel is needed. This method therefore enables the determination of the ground state phase of a spin-2 87Rb BEC at zero magnetic field, which is considered to lie in the immediate vicinity of the boundary between the antiferromagnetic and cyclic phases. We also show that the initial state in which relative phases are controlled can be prepared by Raman processes.Comment: 12 pages, 6 figure

Signal estimation and threshold optimization using an array of bithreshold elements

We consider the problem of optimizing signal transmission through multi-channel noisy devices. We investigate an array of bithreshold noisy devices which are connected in parallel and convergent on a summing center. Utilizing the concept of noise-induced linearization we derive an analytical approximation of the normalized power norm and clarify the relation between the optimum threshold and the standard deviation of noises. We show that the optimum threshold value is 0.63 times the standard deviation of the noises. This relation is applicable to both subthreshold and suprathreshold inputs.Comment: 14 pages, 6 figure

Weakly coupled s=1/2s = 1/2 quantum spin singlets in Ba3_{3}Cr2_{2}O8_{8}

Using single crystal inelastic neutron scattering with and without application of an external magnetic field and powder neutron diffraction, we have characterized magnetic interactions in Ba$_3$Cr$_2$O$_8$. Even without field, we found that there exist three singlet-to-triplet excitation modes in $(h,h,l)$ scattering plane. Our complete analysis shows that the three modes are due to spatially anisotropic interdimer interactions that are induced by local distortions of the tetrahedron of oxygens surrounding the Jahn-Teller active Cr$^{5+} (3d^1)$. The strong intradimer coupling of $J_0 = 2.38(2)$ meV and weak interdimer interactions ($|J_{\rm inter}| \leq 0.52(2)$ meV) makes Ba$_3$Cr$_2$O$_8$ a good model system for weakly-coupled $s = 1/2$ quantum spin dimers

Orbital and spin chains in ZnV2O4

Our powder inelastic neutron scattering data indicate that \zvo is a system of spin chains that are three dimensionally tangled in the cubic phase above 50 K due to randomly occupied $t_{2g}$ orbitals of V$^{3+}$ ($3d^2$) ions. Below 50 K in the tetragonal phase, the chains become straight due to antiferro-orbital ordering. This is evidenced by the characteristic wave vector dependence of the magnetic structure factor that changes from symmetric to asymmetric at the cubic-to-tetragonal transition

Spontaneous magnetization and structure formation in a spin-1 ferromagnetic Bose-Einstein condensate

Motivated by recent experiments involving the non-destructive imaging of magnetization of a spin-1 87Rb Bose gas (Higbie et al., cond-mat/0502517), we address the question of how the spontaneous magnetization of a ferromagnetic BEC occurs in a spin-conserving system. Due to competition between the ferromagnetic interaction and the total spin conservation, various spin structures such as staggered magnetic domains, and helical and concentric ring structures are formed, depending on the geometry of the trapping potential.Comment: 8 pages, 5 figure

First Forcer results on deep-inelastic scattering and related quantities

We present results on the fourth-order splitting functions and coefficient functions obtained using Forcer, a four-loop generalization of the Mincer program for the parametric reduction of self-energy integrals. We have computed the respective lowest three even-N and odd-N moments for the non-singlet splitting functions and the non-singlet coefficient functions in electromagnetic and nu+nu(bar) charged-current deep-inelastic scattering, and the N=2 and N=4 results for the corresponding flavour-singlet quantities. Enough moments have been obtained for an LLL-based determination of the analytic N-dependence of the nf^3 and nf^2 parts, respectively, of the singlet and non-singlet splitting functions. The large-N limit of the latter provides the complete nf^2 contributions to the four-loop cusp anomalous dimension. Our results also provide additional evidence of a non-vanishing contribution of quartic group invariants to the cusp anomalous dimension.Comment: 11 pages, LaTeX (PoS style), 4 eps-figures. To appear in the proceedings of `Loops & Legs 2016', Leipzig (Germany), April 201