105 research outputs found
Ion beam synthesis of nanothermochromic diffraction gratings with giant switching contrast at telecom wavelengths
Nanothermochromic diffraction gratings based on the metal-insulator
transition of are fabricated by site-selective ion beam
implantation in a 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 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 surface acoustic wave resonator is fabricated by heterointegration.
High acoustic quality factors are demonstrated for an operation
frequency MHz. The measured large quality factor-frequency
products ensures the suppression of decoherence due to
thermal noise for temperatures exceeding . 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
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