We present the demonstration of two novel chip-scale FMCW LiDAR optical engines in which all photonic components, including the laser sources, were integrated on single silicon chips. Using the first LiDAR chip design, with an integrated distributed Bragg reflector laser and grating couplers as input/output ports for the receive/transmit light, we demonstrated a maximum range of 28 m limited by transmit light output power of 2 mW. We further demonstrated a maximum range of 75 m using a second LiDAR chip architecture having an on-chip sampled grating distributed Bragg reflector master laser with integrated power amplifier in which the local oscillator light was obtained from the laser back facet. This maximum range can be further increased by improving the laser linewidth. The measured range dependence of the FMCW signal level for both LiDAR chips agreed well with theory. The chip-scale FMCW LiDAR optical engines can be used in conjunction with a variety of off-chip two dimensional beam scanners to realize a chip-scale scanning LiDAR solution. To the best of our knowledge, this is the first published demonstration of fully integrated FMCW LiDAR optical engines on a single silicon chip.

This paper presents the reversible actuation of alkali vapor pressure using devices based on the solid electrolyte beta”-alumina. We demonstrate electrical actuation that gives a dynamic range of 20X in the alkali vapor density in 1 s, which is a IOX improvement over prior work. This is achieved through a combination of low alkali adsorption energy cell-wall coatings, finer sub-micron pitch electrodes, and elevated device operation temperature. This is an enabling component technology for compact atomic clocks and sensors.

We analyze how the performance of a quantum-repeater network depends on the protocol employed to distribute entanglement, and we find that the choice of repeater-to-repeater link protocol has a profound impact on communication rate as a function of hardware parameters. We develop numerical simulations of quantum networks using different protocols, where the repeater hardware is modeled in terms of key performance parameters, such as photon generation rate and collection efficiency. These parameters are motivated by recent experimental demonstrations in quantum dots, trapped ions, and nitrogen-vacancy centers in diamond. We find that a quantum-dot repeater with the newest protocol ("MidpointSource") delivers the highest communication rate when there is low probability of establishing entanglement per transmission, and in some cases the rate is orders of magnitude higher than other schemes. Our simulation tools can be used to evaluate communication protocols as part of designing a large-scale quantum network.

We demonstrate the extension of coherence between all four two-electron spin ground states of an InAs quantum dot molecule (QDM) via nonlocal suppression of nuclear spin fluctuations in two vertically stacked quantum dots (QDs), while optically addressing only the top QD transitions. Long coherence times are revealed through dark-state spectroscopy as resulting from nuclear spin locking mediated by the exchange interaction between the QDs. Line shape analysis provides the first measurement of the quieting of the Overhauser field distribution correlating with reduced nuclear spin fluctuations.

We propose and analyze an optically loaded quantum memory exploiting capacitive coupling between self-assembled quantum dot molecules and electrically gated quantum dot molecules. The self-assembled dots are used for spin-photon entanglement, which is transferred to the gated dots for long-term storage or processing via a teleportation process heralded by single-photon detection. We illustrate a device architecture enabling this interaction and we outline its operation and fabrication. We provide self-consistent Poisson-Schroedinger simulations to establish the design viability and refine the design, and to estimate the physical coupling parameters and their sensitivities to dot placement. The device we propose generates heralded copies of an entangled state between a photonic qubit and a solid-state qubit with a rapid reset time upon failure. The resulting fast rate of entanglement generation is of high utility for heralded quantum networking scenarios involving lossy optical channels.

Two electron spins in quantum dots coupled through coherent tunneling are generally acknowledged to approximately obey Heisenberg isotropic exchange. This has not been established for two holes. Here we measure the spectra of two holes and of two electrons in two vertically stacked self-assembled InAs quantum dots using optical spectroscopy as a function of electric and magnetic fields. We find that the exchange is approximately isotropic for both systems, but that significant asymmetric contributions, arising from spin-orbit and Zeeman interactions combined with spatial asymmetries, are required to explain large anticrossings and fine-structure energy splittings in the spectra. Asymmetric contributions to the isotropic Hamiltonian for electrons are of the order of a few percent while those for holes are an order of magnitude larger.

A single hole spin in a semiconductor quantum dot has emerged as a quantum bit that is potentially superior to an electron spin. A key feature of holes is that they have a greatly reduced hyperfine interaction with nuclear spins, which is one of the biggest difficulties in working with an electron spin. It is now essential to show that holes are viable for quantum information processing by demonstrating fast quantum gates and scalability. To this end, we have developed InAs/GaAs quantum dots coupled through coherent tunnelling and charged with controlled numbers of holes. We report fast, single-qubit gates using a sequence of short laser pulses. We then take the important next step towards scalability of quantum information by optically controlling two interacting hole spins in separate dots.

Using continuous-wave lasers and picosecond optical pulses, we demonstrate initialization, single qubit gates, and two qubit gates in a system of two electron spins in separate tunnel-coupled InAs quantum dots.

Site-selective epitaxy and standard electron beam lithography techniques are employed to spatially couple small InAs/InP quantum dot ensembles to 2D photonic crystal membrane cavities. The small InAs quantum dot ensembles, consisting of just a few dots, are localized to areas similar to 100x100nm(2) at predetermined positions dictated by a nanotemplate consisting of InP pyramids. The dots are embedded in a 2D membrane using a planarization growth step and single missing-hole defect cavities are fabricated in the membrane with the defect sites centered on the dot ensembles. This spatially couples the ensembles to the x-dipole mode of the cavities. Emission from the cavities shows the expected mode structure, with quality factors of 2000.

Here we review the basic optical spectra of quantum dot molecules. We apply a simple and straightforward model to calculate charge stability regions in vertically coupled double dot molecules that are embedded in a Schottky diode. This model allows us to relate features in the optical spectrum to the diode structure. The underlying concepts allow one to design quantum dot molecules functionalized for optical operations.

Photoluminescence data from single self-assembled InAs/InP quantum dots in magnetic fields up to 7 T are presented. Exciton g factors are obtained for dots of varying height, corresponding to ground-state emission energies ranging from 780 to 1100 meV. A monotonic increase in the g factor from -2 to +1.2 is observed as the dot height decreases. The trend is well reproduced by sp(3) tight-binding calculations, which show that the hole g factor is sensitive to confinement effects through orbital angular-momentum mixing between the light-hole and heavy-hole valence bands. We demonstrate tunability of the exciton g factor by manipulating the quantum dot dimensions using pyramidal InP nanotemplates.

A crucial pre-requisite for quantum information applications is the ability to produce a scalable quantum system that can be controllably manipulated. We present a technique that promises the practical realization of a scalable system with arrays of gated quantum dots (QDs) emitting at wavelengths suitable for fibre based quantum cryptography. We show how the random nature of the nucleation site for self-assembled QDs can be overcome by a nanotemplate deposition technique such that further processing around these dots can be performed. By knowing exactly where the QD is, we position electrostatic gates around the dot with better than 30nm accuracy. With these gates and a Si n-doped back gate, we demonstrate from both simulation and experiment that we can control the electron number of the dot via vertical electric fields.

The spin of an electron in a self-assembled InAs/GaAs quantum dot molecule is optically prepared and measured through the trion triplet states. A longitudinal magnetic field is used to tune two of the trion states into resonance, forming a superposition state through asymmetric spin exchange. As a result, spin-flip Raman transitions can be used for optical spin initialization, while separate trion states enable cycling transitions for nondestructive measurement. With two-laser transmission spectroscopy we demonstrate both operations simultaneously, something not previously accomplished in a single quantum dot.

We present optical spectra from numerous, single, self-assembled InAs/InP quantum dots. More than 50 individual dots are studied that emit in the 1.1-1.6 mu m wavelength range. The dots are of high optical quality as judged by the clean, single exciton emission line at low power, the resolution limited linewidth, and the brightness. Each dot exhibits similar trends in the power evolution spectra, despite large variations in height and diameter. The level splittings in the p-shell increase with decreasing height, which we interpret to be from dot elongation along the [011] direction. The evolution of the spectra with increasing power agrees well with predictions from effective bond orbital calculations. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly ordered GaAs nanodot arrays were successfully grown on GaAs (001) substrates through anodic nanochannel alumina masks using molecular beam epitaxy. These nanodot arrays replicate the hexagonal lattice pattern with period spacing of 100nm on the nanochannel alumina mask. The dots also retain the circular shape and good size uniformity of the nanopores on the mask, and the dot size is adjustable by controlling the pore size of the mask. The selectivity of GaAs growth on the GaAs surface exposed under the nanoholes compared with GaAs deposition on the Al2O3 mask increases with reducing growth rate. This approach provides a low cost means for fabricating novel arrays of quantum nanostructures.

Gallium oxide thin films deposited by electron cyclotron resonance plasma molecular beam epitaxy on GaAs(110) surfaces are reported. Room temperature photoluminescence spectra show an enhancement over as-is surfaces by greater than an order of magnitude for semi-insulating wafers. This enhancement is corroborated by low temperature photoluminescence spectra, showing a reduction in AsGa, OAs, and carbon-related emissions. The bonding configuration at the interface to GaAs was investigated by x-ray photoelectron spectroscopy depth profiling and secondary ion mass spectroscopy: Arsenic oxide related compounds were below the sensitivity limits of the former technique, while carbon (both in the film and in the vicinity of the interface) was below the sensitivity limit of the latter technique. Photoluminescence enhancement is also attributed to hydrogen passivation of EL2 defects, which is found to be stable following deposition at temperatures of 400 °C on semi-insulating and p-type wafers.