Cross-Kerr-based information transfer processes

The realization of nonclassical states is an important task for many applications of quantum information processing. Usually, properly tailored interactions, different from goal to goal, are considered in order to accomplish specific tasks within the general framework of quantum state engineering. In this paper we remark on the flexibility of a cross-Kerr nonlinear coupling in hybrid systems as an important ingredient in the engineering of nonclassical states. The general scenario we consider is the implementation of high cross-Kerr nonlinearity in cavity-quantum electrodynamics. In this context, we discuss the possibility of performing entanglement transfer and swapping between a qubit and a continuous-variable state. The recently introduced concept of entanglement reciprocation is also considered and shown to be possible with our scheme. We reinterpret some of our results in terms of applications of a generalized Ising interaction to systems of different nature.Comment: 8 pages, 4 figures, RevTeX

Nonfrustrated magnetoelectric with incommensurate magnetic order in magnetic field

We discuss a model nonfrustrated magnetoelectric in which strong enough magnetoelectric coupling produces incommensurate magnetic order leading to ferroelectricity. Properties of the magnetoelectric in magnetic field directed perpendicular to wave vector describing the spin helix are considered in detail. Analysis of classical energy shows that in contrast to naive expectation the onset of ferroelectricity takes place at a field $H_{c1}$ that is lower than the saturation field $H_{c2}$. One has $H_{c1}=H_{c2}$ at strong enough magnetoelectric coupling. We show that at H=0 the ferroelectricity appears at $T=T_{FE}<T_N$. Qualitative discussion of phase diagram in $H-T$ plane is presented within mean field approach.Comment: 12 pages, 3 figures, accepted in JET

Magnetic Order and Spin Dynamics in Ferroelectric HoMnO3_{3}

Hexagonal HoMnO$_{3}$ is a frustrated antiferromagnet (T$_{N}$=72 K) ferroelectric (T$_{C}$=875 K) in which these two order parameters are coupled. Our neutron measurements of the spin wave dispersion for the S=2 Mn$^{3+}$ on the layered triangular lattice are well described by a two-dimensional nearest-neighbor Heisenberg exchange J=2.44 meV, and an anisotropy $D$ that is 0.093 meV above the spin reorientation transition at 40 K, and 0.126 meV below. For $H\parallel c$ the magnetic structures and phase diagram have been determined, and reveal additional transitions below 8 K where the ferroelectrically displaced Ho$^{3+}$ ions are ordered magnetically.Comment: To be published in Physical Review Letter

Melting of Quasi-Two-Dimensional Charge Stripes in La5/3Sr1/3NiO4

Commensurability effects for nickelates have been studied by the first neutron experiments on La5/3Sr1/3NiO4. Upon cooling, this system undergoes three successive phase transitions associated with quasi-two-dimensional (2D) commensurate charge and spin stripe ordering in the NiO$_2$ planes. The two lower temperature phases (denoted as phase II and III) are stripe lattice states with quasi-long-range in-plane charge correlation. When the lattice of 2D charge stripes melts, it goes through an intermediate glass state (phase I) before becoming a disordered liquid state. This glass state shows short-range charge order without spin order, and may be called a "stripe glass" which resembles the hexatic/nematic state in 2D melting.Comment: 10 pages, RevTex, 4 figures available on request to [email protected]

Electromagnons in multiferroic YMn2O5 and TbMn2O5

Based on temperature dependent far infrared transmission spectra of YMn2O5 and TbMn2O5 single crystals, we report the observation of electric dipole-active magnetic excitations, or electromagnons, in these multiferroics. Electromagnons are found to be directly responsible for the step-like anomaly of the static dielectric constant at the commensurate--incommensurate magnetic transition and are the origin of the colossal magneto-dielectric effect reported in these multiferroics.Comment: 4 pages, 4 figures, submitte