Ion beam synthesis of nanothermochromic diffraction gratings with giant switching contrast at telecom wavelengths

Nanothermochromic diffraction gratings based on the metal-insulator transition of $\mathrm{VO_2}$ are fabricated by site-selective ion beam implantation in a $\mathrm{SiO_2}$ matrix. Gratings were defined either (i) directly by spatially selective ion beam synthesis or (ii) by site-selective deactivation of the phase transition by ion beam induced defects. The strongest increase of the diffracted light intensities was observed at a wavelength of 1550\,nm exceeding a factor of 20 for the selectively deactivated gratings. The observed pronounced thermal hysteresis extending down close to room temperature makes this system ideally suited for optical memory applications.Comment: 4 pages, 3 figures, 1 table - corrected Figure

Site-selective ion beam synthesis and optical properties of individual CdSe nanocrystal quantum dots in a SiO2 matrix

Cadmium selenide nanocrystal quantum dots (NC-QDs) are site-selectively synthesized by sequential ion beam implantation of selenium and cadmium ions in a SiO2 matrix through sub-micron apertures followed by a rapid thermal annealing step. The size, areal density and optical emission energy of the NC-QDs are controlled by the ion fluence during implantation and the diameter of implantation aperture. For low fluences and small apertures the emission of these optically active emitters is blue-shifted compared to that of the bulk material by $>100\,{\rm meV}$ due to quantum confinement. The emission exhibits spectral diffusion and blinking on a second timescales as established also for solution synthesized NC-QDs

Near-infrared saturable and reverse saturable absorption of ion beam synthesized VO2 nanocrystals

We investigate the nonlinear optical response of a thin film of ion-implanted VO2 nanocrystals with open aperture z-scans involving femtosecond near-infrared pulses. Beyond the established nonlinearity related to the insulator-metal phase transition of VO2, the metallic state features a pronounced saturable absorption for 100 fs pulses from a modelocked Yb:fiber source at = 1036 nm. In contrast, we find a pronounced reverse saturable absorption for 90 fs pulses in the telecom window at = 1550 nm. We attribute these nonlinearities to a transient red-shift of the plasmonic resonance of the nanocrystals, in line with the temperature dependence of the linear absorption and the theoretical expectation for electronic heating. Details of the transmissivity characteristics can be tailored by the lattice temperature and/or the size of the nanocrystals. The results hold promise for the use of VO2 nanocrystals as a saturable absorber, e.g., to mode-locked near-infrared lasers

A hybrid (Al)GaAs-LiNbO3 surface acoustic wave resonator for cavity quantum dot optomechanics

A hybrid device comprising a (Al)GaAs quantum dot heterostructure and a LiNbO$_3$ surface acoustic wave resonator is fabricated by heterointegration. High acoustic quality factors $Q>4000$ are demonstrated for an operation frequency $f\approx 300$ MHz. The measured large quality factor-frequency products $Q\times f>10^{12}$ ensures the suppression of decoherence due to thermal noise for temperatures exceeding $T>50\,\mathrm{K}$. Frequency and position dependent optomechanical coupling of single quantum dots and the resonator modes is observed.Comment: Accepted manuscrip

Dynamic acousto-mechanical control of a strongly coupled photonic molecule

Two-dimensional photonic crystal membranes provide a versatile planar architecture for integrated photonics to control the propagation of light on a chip employing high quality optical cavities, waveguides, beamsplitters or dispersive elements. When combined with highly non-linear quantum emitters, quantum photonic networks operating at the single photon level come within reach. Towards large-scale quantum photonic networks, selective dynamic control of individual components and deterministic interactions between different constituents are of paramount importance. This indeed calls for switching speeds ultimately on the system's native timescales. For example, manipulation via electric fields or all-optical means have been employed for switching in nanophotonic circuits and cavity quantum electrodynamics studies. Here, we demonstrate dynamic control of the coherent interaction between two coupled photonic crystal nanocavities forming a photonic molecule. By using an electrically generated radio frequency surface acoustic wave we achieve optomechanical tuning, demonstrate operating speeds more than three orders of magnitude faster than resonant mechanical approaches. Moreover, the tuning range is large enough to compensate for the inherent fabrication-related cavity mode detuning. Our findings open a route towards nanomechanically gated protocols, which hitherto have inhibited the realization in all-optical schemes.Comment: submitted manuscrip

Dynamic modulation of photonic crystal nanocavities using gigahertz acoustic phonons

Photonic crystal membranes (PCM) provide a versatile planar platform for on-chip implementations of photonic quantum circuits. One prominent quantum element is a coupled system consisting of a nanocavity and a single quantum dot (QD) which forms a fundamental building block for elaborate quantum information networks and a cavity quantum electrodynamic (cQED) system controlled by single photons. So far no fast tuning mechanism is available to achieve control within the system coherence time. Here we demonstrate dynamic tuning by monochromatic coherent acoustic phonons formed by a surface acoustic wave (SAW) with frequencies exceeding 1.7 gigahertz, one order of magnitude faster than alternative approaches. We resolve a periodic modulation of the optical mode exceeding eight times its linewidth, preserving both the spatial mode profile and a high quality factor. Since PCMs confine photonic and phononic excitations, coupling optical to acoustic frequencies, our technique opens ways towards coherent acoustic control of optomechanical crystals.Comment: 11 pages 4 figure

Resonance-fluorescence spectral dynamics of an acoustically modulated quantum dot

Quantum technologies that rely on photonic qubits require a precise controllability of their properties. For this purpose hybrid approaches are particularly attractive because they offer a large flexibility to address different aspects of the photonic degrees of freedom. When combining photonics with other quantum platforms like phonons, quantum transducers have to be realized that convert between the mechanical and optical domain. Here, we realize this interface between phonons in the form of surface acoustic waves (SAWs) and single photons, mediated by a single semiconductor quantum dot exciton. In this combined theoretical and experimental study, we show that the different sidebands exhibit characteristic blinking dynamics that can be controlled by detuning the laser from the exciton transition. By developing analytical approximations we gain a better understanding of the involved internal dynamics. Our specific SAW approach allows us to reach the ideal frequency range of around 1 GHz that enables simultaneous temporal and spectral phonon sideband resolution close to the combined fundamental time-bandwidth limit

Electrical control of inter-dot electron tunneling in a quantum dot molecule

We employ ultrafast pump-probe spectroscopy to directly monitor electron tunneling between discrete orbital states in a pair of spatially separated quantum dots. Immediately after excitation, several peaks are observed in the pump-probe spectrum due to Coulomb interactions between the photo-generated charge carriers. By tuning the relative energy of the orbital states in the two dots and monitoring the temporal evolution of the pump-probe spectra the electron and hole tunneling times are separately measured and resonant tunneling between the two dots is shown to be mediated both by elastic and inelastic processes. Ultrafast (< 5 ps) inter-dot tunneling is shown to occur over a surprisingly wide bandwidth, up to ~8 meV, reflecting the spectrum of exciton-acoustic phonon coupling in the system