Nonequilibrium phases in hybrid arrays with flux qubits and NV centers

We propose a startling hybrid quantum architecture for simulating a localization-delocalization transition. The concept is based on an array of superconducting flux qubits which are coupled to a diamond crystal containing nitrogen-vacancy (NV) centers. The underlying description is a Jaynes-Cummings-lattice in the strong-coupling regime. However, in contrast to well-studied coupled cavity arrays the interaction between lattice sites is mediated here by the qubit rather than by the oscillator degrees of freedom. Nevertheless, we point out that a transition between a localized and a delocalized phase occurs in this system as well. We demonstrate the possibility of monitoring this transition in a non-equilibrium scenario, including decoherence effects. The proposed scheme allows the monitoring of localization-delocalization transitions in Jaynes-Cummings-lattices by use of currently available experimental technology. Contrary to cavity-coupled lattices, our proposed recourse to stylized qubit networks facilitates (i) to investigate localization-delocalization transitions in arbitrary dimensions and (ii) to tune the inter-site coupling in-situ.Comment: Version to be published in Phys. Rev.

Cavity-enhanced Raman Microscopy of Individual Carbon Nanotubes

Raman spectroscopy reveals chemically specific information and provides label-free insight into the molecular world. However, the signals are intrinsically weak and call for enhancement techniques. Here, we demonstrate Purcell enhancement of Raman scattering in a tunable high-finesse microcavity, and utilize it for molecular diagnostics by combined Raman and absorption imaging. Studying individual single-wall carbon nanotubes, we identify crucial structural parameters such as nanotube radius, electronic structure and extinction cross-section. We observe a 320-times enhanced Raman scattering spectral density and an effective Purcell factor of 6.2, together with a collection efficiency of 60%. Potential for significantly higher enhancement, quantitative signals, inherent spectral filtering and absence of intrinsic background in cavity-vacuum stimulated Raman scattering render the technique a promising tool for molecular imaging. Furthermore, cavity-enhanced Raman transitions involving localized excitons could potentially be used for gaining quantum control over nanomechanical motion and open a route for molecular cavity optomechanics

Physik am Schlagzeug

Das Schlagzeug ist für Schüler ein sehr attraktives Musikinstrument und Schlaginstrumente bieten vielfältige Möglichkeiten, akustisch relevante Vorgänge zu beobachten. Dazu gehören das Sichtbarmachen der Schwingung der Becken und der Fellmembran mittels einer Hochgeschwindigkeitskamera oder mittels Chladnischer Klangfiguren, die durch eine Schwingungsanregung auf sandbestreuten Fellen und Platten entstehen. Eine Software zur Klanganalyse und Klangvisualisierung bietet zudem die Möglichkeit, die Klänge der Schlaginstrumente hinsichtlich verschiedener physikalischer Messgrößen zu untersuchen. Im Mechanikunterricht kann aber auch die Bewegung des Sticks mit einer Hochgeschwindigkeitskamera und einer Videoanalysesoftware als komplexe Bewegung untersucht werden. Im Folgenden werden verschiedene Versuche vorgestellt, die auch von Schülern durchgeführt werden können

Physik am Schlagzeug

Das Schlagzeug ist für Schüler ein sehr attraktives Musikinstrument und Schlaginstrumente bieten vielfältige Möglichkeiten, akustisch relevante Vorgänge zu beobachten. Dazu gehören das Sichtbarmachen der Schwingung der Becken und der Fellmembran mittels einer Hochgeschwindigkeitskamera oder mittels Chladnischer Klangfiguren, die durch eine Schwingungsanregung auf sandbestreuten Fellen und Platten entstehen. Eine Software zur Klanganalyse und Klangvisualisierung bietet zudem die Möglichkeit, die Klänge der Schlaginstrumente hinsichtlich verschiedener physikalischer Messgrößen zu untersuchen. Im Mechanikunterricht kann aber auch die Bewegung des Sticks mit einer Hochgeschwindigkeitskamera und einer Videoanalysesoftware als komplexe Bewegung untersucht werden. Im Folgenden werden verschiedene Versuche vorgestellt, die auch von Schülern durchgeführt werden können

Transverse-mode coupling effects in scanning cavity microscopy

Tunable open-access Fabry–Pérot microcavities enable the combination of cavity enhancement with high resolution imaging. To assess the limits of this technique originating from background variations, we perform high-finesse scanning cavity microscopy of pristine planar mirrors. We observe spatially localized features of strong cavity transmission reduction for certain cavity mode orders, and periodic background patterns with high spatial frequency. We show in detailed measurements that the localized structures originate from resonant transverse-mode coupling and arise from the topography of the planar mirror surface, in particular its local curvature and gradient. We further examine the background patterns and find that they derive from non-resonant mode coupling, and we attribute it to the micro roughness of the mirror. Our measurements and analysis elucidate the impact of imperfect mirrors and reveal the influence of their microscopic topography. This is crucial for the interpretation of scanning cavity images, and could provide relevant insight for precision applications such as gravitational wave detectors, laser gyroscopes, and reference cavities

Weak and strong coupling regimes in plasmonic QED

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).We present a quantum theory for the interaction of a two-level emitter with surface plasmon polaritons confined in single-mode waveguide resonators. Based on the Green's function approach, we develop the conditions for the weak and strong coupling regimes by taking into account the sources of dissipation and decoherence: radiative and nonradiative decays, internal loss processes in the emitter, as well as propagation and leakage losses of the plasmons in the resonator. The theory is supported by numerical calculations for several quantum emitters, GaAs and CdSe quantum dots, and nitrogen vacancy (NV) centers together with different types of resonators constructed of hybrid, cylindrical, or wedge waveguides. We further study the role of temperature and resonator length. Assuming realistic leakage rates, we find the existence of an optimal length at which strong coupling is possible. Our calculations show that the strong coupling regime in plasmonic resonators is accessible within current technology when working at very low temperatures (≲4 K). In the weak coupling regime, our theory accounts for recent experimental results. By further optimization we find highly enhanced spontaneous emission with Purcell factors over 1000 at room temperature for NV centers. We finally discuss more applications for quantum nonlinear optics and plasmon-plasmon interactions. © 2013 American Physical Society.This work was supported by Spanish MICINN Projects No. FIS2011-25167, No. MAT2011-28581-C02, and No. CSD2007-046-Nanolight.es. F.J.G.-V. acknowledges financial support by the European Research Council, Grant No. 290981 (PLASMONANOQUANTA).Peer Reviewe

A highly stable and fully tunable open microcavity platform at cryogenic temperatures

Open-access microcavities are a powerful tool to enhance light–matter interactions for solid-state quantum and nanosystems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements—full tunability to cope with spatial and spectral inhomogeneities of a material and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully tunable, open-access, fiber-based Fabry–Pérot microcavity platform that can be operated under increased noise levels in a closed-cycle cryostat. It comprises custom-designed monolithic micro- and nanopositioning elements with up to mm-scale travel range that achieve a passive cavity length stability at low temperature of only 15 pm rms in a closed-cycle cryostat and 5 pm in a more quiet flow cryostat. This can be further improved by active stabilization, and even higher stability is obtained under direct mechanical contact between the cavity mirrors, yielding 0.8 pm rms during the quiet phase of the closed-cycle cryocooler. The platform provides the operation of cryogenic cavities with high finesse and small mode volume for strong enhancement of light–matter interactions, opening up novel possibilities for experiments with a great variety of quantum and nanomaterials

Transverse-mode coupling and diffraction loss in tunable Fabry-Perot microcavities

We report on measurements and modeling of the mode structure of tunable Fabry-Perot optical microcavities with imperfect mirrors. We find that non-spherical mirror shape and finite mirror size leave the fundamental mode mostly unaffected, but lead to loss, mode deformation, and shifted resonance frequencies at particular mirror separations. For small mirror diameters, the useful cavity length is limited to values significantly below the expected stability range. We explain the observations by resonant coupling between different transverse modes of the cavity and mode-dependent diffraction loss. A model based on resonant state expansion that takes into account the measured mirror profile can reproduce the measurements and identify the parameter regime where detrimental effects of mode mixing are avoided