Adiabatic Control of Spin-Wave Propagation using Magnetisation Gradients

Spin waves are of large interest as data carriers for future logic devices. However, due to the strong anisotropic dispersion relation of dipolar spin-waves in in-plane magnetised films the realisation of two-dimensional information transport remains a challenge. Bending of the energy flow is prohibited since energy and momentum of spin waves cannot be conserved while changing the direction of wave propagation. Thus, non-linear or non-stationary mechanisms are usually employed. Here, we propose to use reconfigurable laser-induced magnetisation gradients to break the system's translational symmetry. The resulting changes in the magnetisation shift the dispersion relations locally and allow for operating with different spin-wave modes at the same frequency. Spin-wave momentum is first transformed via refraction at the edge of the magnetisation gradient region and then adiabatically modified inside it. Along these lines the spin-wave propagation direction can be controlled in a broad frequency range with high efficiency

Nonlinear spectroscopy of exciton-polaritons in a GaAs-based microcavity

We present a systematic investigation of two-photon excitation processes in a GaAs-based microcavity in the strong-coupling regime. We observe second harmonic generation resonant to the upper and lower polariton level, which exhibits a strong dependence on the photonic fraction of the corresponding polariton. In addition we have performed two-photon excitation spectroscopy to identify $2p$ exciton states which are crucial for the operation as a terahertz lasing device, which was suggested recently [A. V. Kavokin et al., Phys. Rev. Lett. \textbf{108}, 197401 (2012)]. However, no distinct signatures of a $2p$ exciton state could be identified, which indicates a low two-photon pumping efficiency

Quantum-Optically Enhanced STORM (QUEST) for Multi-Emitter Localization

Super-resolution imaging has introduced new capabilities to investigate processes at the nanometer scale by optical means. However, most super-resolution techniques require either sparse excitation of few emitters or analysis of high-order cumulants in order to identify several emitters in close vicinity. Here, we present an approach that draws upon methods from quantum optics to perform localization super-resolution imaging of densely packed emitters and determine their number automatically: Quantum-optically enhanced STORM (QUEST). By exploiting normalized photon correlations, we predict a localization precision below 30 nm or better even for closely spaced emitter up to a density of 125 emitters per μm at photon emission rates of 105 photons per second and emitter. Our technique does not require complex experimental arrangements and relies solely on spatially resolved time streams of photons and subsequent data analysis

Influence of interactions with non-condensed particles on the coherence of a 1D polariton condensate

One-dimensional polariton condensates (PoCos) in a photonic wire are generated through non-resonant laser excitation, by which also a reservoir of background carriers is created. Interaction with this reservoir may affect the coherence of the PoCo, which is studied here by injecting a condensate locally and monitoring the coherence along the wire. While the incoherent reservoir is mostly present within the excitation laser spot, the condensate can propagate ballistically through the wire. Photon correlation measurements show that far from the laser spot the second order correlation function approaches unity value, as expected for the coherent condensed state. When approaching the spot, however, the correlation function increases up to values of 1.2 showing the addition of noise to the emission due to interaction with the reservoir. This finding is substantiated by measuring the first order coherence by a double slit experiment, which shows a reduced visibility of interference at the excitation laser spot.Comment: 8 pages, 8 figure