Mean-field approaches to the Bose-Hubbard model with three-body local interaction

The zero temperature properties of the generalized Bose-Hubbard model including three-body interactions are studied on a mean-field level. We obtain analytical results using the so-called perturbative mean-field method and more detailed numerical results using the Gutzwiller product state variational Ansatz. These two approaches yield equivalent results which compare well on a qualitative level with recent exact results obtained in the literature.Comment: Proceedings of the CEWQO 201

Two-way teleportation

A protocol for teleporting two qudits simultaneously in opposite directions using a single pair of maximally entangled qudits is presented. This procedure works provided that the product of dimensions of the two qudits to be teleported does not exceed the dimension of the individual qudits in the maximally entangled pair

Stabilized parametric Cooper-pair pumping in a linear array of coupled Josephson junctions

We present an experimentally realizable stabilized charge pumping scheme in a linear array of Cooper-pair boxes. The system design intrinsically protects the pumping mechanism from severe errors, especially current reversal and spontaneous charge excitation. The quantum Zeno effect is implemented to further diminish pumping errors. The characteristics of this scheme are considered from the perspective of improving the current standard. Such an improvement bears relevence to the closure of the so-called measurement triangle (see D. Averin [Nature 434, 285 (2005)]).Comment: Title changed, other corrections and modifications requested from Phys. Rev. Let

Multiparameter estimation perspective on non-Hermitian singularity-enhanced sensing

Describing the evolution of quantum systems by means of non-Hermitian generators opens a new avenue to explore the dynamical properties naturally emerging in such a picture, e.g. operation at the so-called exceptional points, preservation of parity-time symmetry, or capitalising on the singular behaviour of the dynamics. In this work, we focus on the possibility of achieving unbounded sensitivity when using the system to sense linear perturbations away from a singular point. By combining multiparameter estimation theory of Gaussian quantum systems with the one of singular-matrix perturbations, we introduce the necessary tools to study the ultimate limits on the precision attained by such singularity-tuned sensors. We identify under what conditions and at what rate can the resulting sensitivity indeed diverge, in order to show that nuisance parameters should be generally included in the analysis, as their presence may alter the scaling of the error with the estimated parameter.Comment: 16 pages with appendices. Comments are more than welcom