8 research outputs found
Observation of Hysteretic Transport Due to Dynamic Nuclear Spin Polarization in a GaAs Lateral Double Quantum Dot
We report a new transport feature in a GaAs lateral double quantum dot that
emerges only for magnetic field sweeps and shows hysteresis due to dynamic
nuclear spin polarization (DNP). This DNP signal appears in the Coulomb
blockade regime by virtue of the finite inter-dot tunnel coupling and
originates from the crossing between ground levels of the spin triplet and
singlet extensively used for nuclear spin manipulations in pulsed gate
experiments. The unexpectedly large signal intensity is suggestive of
unbalanced DNP between the two dots, which opens up the possibility of
controlling electron and nuclear spin states via DC transport.Comment: 5 pages, 4 figure
Stimulated emission from multilayer graphene
Monolayer graphene absorbs 2.3 percent of the incident visible light.
This "small" absorption was used to emphasize visual transparency of graphene,
but in fact it means that multilayer graphene absorbs sizable fraction of
incident light, which causes non-negligible fluorescence. In this paper, we
study the light emission properties of multilayer graphene composed of tens to
hundreds of layers, because these are informative materials having interesting
optical properties correlated closely with fluorescence. For example, it was
recently predicted that 87-layer graphene absorbs infrared light at maximum
efficiency and 20-layer graphene on silicon substrates exhibits zero
reflectance (a total absence of backscattering) at a specific visible light
wavelength. By modeling light emissions from multilayer graphene using a
transfer matrix method, we could quantitatively explain the measured
reflectivity from multilayer graphene on silicon substrates. We found sizable
corrections, that cannot be classified as incoherent light emissions, to the
reflectance of visible light. The new component originates from stimulated
emission caused by absorption at each graphene layer, and it is a coherent sum
over the amplitudes coming from all graphene layers with a common phase shift
of relative to the incident light. The coherent corrections to the
reflectance become dominant for samples thicker than 40-layers and thinner than
160-layers. Multilayer graphene thus functions as a partial coherent light
source of various wavelengths and it may have surface-emitting laser
applications.Comment: 9 pages, 9 figure
Intrinsic and extrinsic origins of low-frequency noise in GaAs/AlGaAs Schottky-gated nanostructures
Optical-referenceless optical frequency counter with twelve-digit absolute accuracy
Abstract A simpler and more accurate measurement of absolute optical frequencies (AOFs) is very important for optical communications and navigation systems. To date, an optical reference has been needed for measuring AOFs with twelve-digit accuracy because of the difficulty in measuring them directly. Here, we focus on an electro-optics-modulation comb that can bridge the vast frequency gap between photonics and electronics. We demonstrate an unprecedented method that can directly measure AOFs to an accuracy of twelve digits with an RF frequency counter by simply delivering a frequency-unknown laser into an optical phase modulator. This could open up a new horizon for optical-referenceless optical frequency metrology. Our method can also simultaneously achieve a 100-fold phase-noise reduction in a conventional signal generator. This corresponds to an increase in the transmission speed of wireless communications of by about seven times
Subā30āfs fibreācoupled electroāoptic modulation comb at 1.5 Ī¼m with a 25āGHz repetition rate
Abstract The generation of a 24āfs fibreācoupled electroāopticāmodulation (EO) comb at 1.5 Ī¼m with a 25āGHz repetition rate, which is the shortest pulse, is demonstrated. The authors also generated a 2/3āoctave spanning supercontinuum spectrum using precise dispersionācontrolled silicon nitride waveguides. This method can open new horizons to generate a compact and robust carrierāenvelopeāoffsetālocked EO comb