Plasmonic nanoantennas as integrated coherent perfect absorbers on SOI waveguides for modulators and all-optical switches

The performance of plasmonic nanoantenna structures on top of SOI wire waveguides as coherent perfect absorbers for modulators and all-optical switches is explored. The absorption, scattering, reflection and transmission spectra of gold and aluminum nanoantenna-loaded waveguides were calculated by means of 3D finite-difference time-domain simulations for single waves propagating along the waveguide, as well as for standing wave scenarios composed from two counterpropagating waves. The investigated configurations showed losses of roughly 1% and extinction ratios greater than 25 dB for modulator and switching applications, as well as plasmon effects such as strong field enhancement and localization in the nanoantenna region. The proposed plasmonic coherent perfect absorbers can be utilized for ultracompact all-optical switches in coherent networks as well as modulators and can find applications in sensing or in increasing nonlinear effects.Comment: 10 pages, 6 figure

Minkowski Vacuum Stress Tensor Fluctuations

We study the fluctuations of the stress tensor for a massless scalar field in two and four-dimensional Minkowski spacetime in the vacuum state. Covariant expressions for the stress tensor correlation function are obtained as sums of derivatives of a scalar function. These expressions allow one to express spacetime averages of the correlation function as finite integrals. We also study the correlation between measurements of the energy density along a worldline. We find that these measurements may be either positively correlated or anticorrelated. The anticorrelated measurements can be interpreted as telling us that if one measurement yields one sign for the averaged energy density, a successive measurement with a suitable time delay is likely to yield a result with the opposite sign.Comment: 24 pages, 5 figures; Some additional comments added in Sect. IIB and a more compact argument given in App.

A simple renormalization group approximation of the groundstate properties of interacting bosonic systems

We present a new, simple renormalization group method of investigating groundstate properties of interacting bosonic systems. Our method reduces the number of particles in a system, which makes numerical calculations possible for large systems. It is conceptually simple and easy to implement, and allows to investigate the properties unavailable through mean field approximations, such as one- and two-particle reduced density matrices of the groundstate. As an example, we model a weakly interacting 1D Bose gas in a harmonic trap. Compared to the mean-field Gross-Pitaevskii approximation, our method provides a more accurate description of the groundstate one-particle density matrix. We have also obtained the Hall-Post lower bounds for the groundstate energy of the gas. All results have been obtained by the straightforward numerical diagonalization of the Hamiltonian matrix.Comment: RevTex 4, 12 figures (revised and updated); to appear in Physical Review

Topological quantum buses: coherent quantum information transfer between topological and conventional qubits

We propose computing bus devices that enable quantum information to be coherently transferred between topological and conventional qubits. We describe a concrete realization of such a topological quantum bus acting between a topological qubit in a Majorana wire network and a conventional semiconductor double quantum dot qubit. Specifically, this device measures the joint (fermion) parity of these two different qubits by using the Aharonov-Casher effect in conjunction with an ancilliary superconducting flux qubit that facilitates the measurement. Such a parity measurement, together with the ability to apply Hadamard gates to the two qubits, allows one to produce states in which the topological and conventional qubits are maximally entangled and to teleport quantum states between the topological and conventional quantum systems.Comment: 5 pages, 2 figures; v2: minor revision