Topological hardcore bosons on the honeycomb lattice

This paper presents a connection between the topological properties of hardcore bosons and that of magnons in quantum spin magnets. We utilize the Haldane-like hardcore bosons on the honeycomb lattice as an example. We show that this system maps to a spin-1/2 quantum XY model with a next-nearest-neighbour Dzyaloshinsky–Moriya interaction. We obtain the magnon excitations of the quantum spin model and compute the edge states, Berry curvature, and thermal and spin Nernst conductivities. Because of the mapping from spin variables to bosons, the hardcore bosons possess the same nontrivial topological properties as those in quantum spin systems. These results are important in the study of magnetic excitations in quantum magnets and they are also useful for understanding the control of ultracold bosonic quantum gases in honeycomb optical lattices, which is experimentally accessible.

1/f NOISE IN ISING QUANTUM COMPUTERS

We study the 1/fα-phenomenon in one- and two-dimensional spin-1/2 lattice models, which have been proposed for realizing scalable quantum computers. Taking the eigenvalue spectrum of the Hamiltonian for the quantum spin model as a discrete-time series, the Fourier power spectrum for the fluctuations in it is analyzed in terms of its frequency. A 1/fα type power-law behavior is observed in both spin models. As the nearest-neighbor interaction strength between the qubits increases, the exponent α across a transition from α = 2 to α = 1.