A nano-power tuneable edge-detection circuit

Published versio

Nano-power mixed-signal tunable edge-detection circuit for pixel-level processing in next generation vision systems

Accepted versio

Mid-infrared quantum optics in silicon

Applied quantum optics stands to revolutionise many aspects of information technology, provided performance can be maintained when scaled up. Silicon quantum photonics satisfies the scaling requirements of miniaturisation and manufacturability, but at 1.55 $\mu$m it suffers from unacceptable linear and nonlinear loss. Here we show that, by translating silicon quantum photonics to the mid-infrared, a new quantum optics platform is created which can simultaneously maximise manufacturability and miniaturisation, while minimising loss. We demonstrate the necessary platform components: photon-pair generation, single-photon detection, and high-visibility quantum interference, all at wavelengths beyond 2 $\mu$m. Across various regimes, we observe a maximum net coincidence rate of 448 $\pm$ 12 Hz, a coincidence-to-accidental ratio of 25.7 $\pm$ 1.1, and, a net two photon quantum interference visibility of 0.993 $\pm$ 0.017. Mid-infrared silicon quantum photonics will bring new quantum applications within reach.Comment: 8 pages, 4 figures; revised figures, updated discussion in section 3, typos corrected, added referenc

A graphene transmon operating at 1 T

A superconducting transmon qubit resilient to strong magnetic fields is an important component for proposed topological and hybrid quantum computing (QC) schemes. Transmon qubits consist of a Josephson junction (JJ) shunted by a large capacitance, coupled to a high quality factor superconducting resonator. In conventional transmon devices, the JJ is made from an Al/AlO$_x$/Al tunnel junction which ceases operation above the critical magnetic field of Al, 10 mT. Alternative junction technologies are therefore required to push the operation of these qubits into strong magnetic fields. Graphene JJs are one such candidate due to their high quality, ballistic transport and electrically tunable critical current densities. Importantly the monolayer structure of graphene protects the JJ from orbital interference effects that would otherwise inhibit operation at high magnetic field. Here we report the integration of ballistic graphene JJs into microwave frequency superconducting circuits to create the first graphene transmons. The electric tunability allows the characteristic band dispersion of graphene to be resolved via dispersive microwave spectroscopy. We demonstrate that the device is insensitive to the applied field and perform energy level spectroscopy of the transmon at 1 T, more than an order of magnitude higher than previous studies.Comment: attached supplementary materia

Design and Development of an Optical Chip Interferometer For High Precision On-Line Surface Measurement

Advances in manufacturing and with the demand of achieving faster throughput at a lower cost in any industrial setting have put forward the need for embedded metrology. Embedded metrology is the provision of metrology on the manufacturing platform, enabling measurement without the removal of the workpiece. Providing closer integration of metrology upon the manufacturing platform will improve material processing and reliability of manufacture for high added value products in ultra-high-precision engineering. Currently, almost all available metrology instrumentation is either too bulky, slow, destructive in terms of damaging the surfaces with a contacting stylus or is carried out off-line. One technology that holds promise for improving the current state-of-the-art in the online measurement of surfaces is hybrid photonic integration. This technique provides for the integration of individual optoelectronic components onto silicon daughter boards which are then incorporated on a silica motherboard containing waveguides to produce a complete photonic circuit. This thesis presents first of its kind a novel chip interferometer sensor based on hybrid integration technology for online surface and dimensional metrology applications. The complete metrology sensor system is structured into two parts; hybrid photonic chip and optical probe. The hybrid photonic chip interferometer is based on a silica-on-silicon etched integrated-optic motherboard containing waveguide structures and evanescent couplers. Upon the motherboard, electro-optic components such as photodiodes and a semiconductor gain block are mounted and bonded to provide the required functionality. Optical probe is a separate entity attached to the integrated optic module which serves as optical stylus for surface scanning in two measurement modes a) A single-point for measuring distance and thus form/surface topography through movement of the device or workpiece, b) Profiling (lateral scanning where assessment of 2D surface parameters may be determined in a single shot. Wavelength scanning and phase shifting inteferometry implemented for the retrival of phase information eventually providing the surface height measurement. The signal analysis methodology for the two measurement modes is described as well as a theoretical and experimental appraisal of the metrology capabilities in terms of range and resolution. The incremetal development of various hybrid photonic modules such as wavelength encoder unit, signal detection unit etc. of the chip interferometer are presented. Initial measurement results from various componets of metrology sensor and the surface measurement results in two measurement modes validate the applicability of the described sensor system as a potential metrology tool for online surface measurement applications

On-chip generation and dynamic piezo-optomechanical rotation of single photons

Integrated photonic circuits are key components for photonic quantum technologies and for the implementation of chip-based quantum devices. Future applications demand flexible architectures to overcome common limitations of many current devices, for instance the lack of tuneabilty or built-in quantum light sources. Here, we report on a dynamically reconfigurable integrated photonic circuit comprising integrated quantum dots (QDs), a Mach-Zehnder interferometer (MZI) and surface acoustic wave (SAW) transducers directly fabricated on a monolithic semiconductor platform. We demonstrate on-chip single photon generation by the QD and its sub-nanosecond dynamic on-chip control. Two independently applied SAWs piezo-optomechanically rotate the single photon in the MZI or spectrally modulate the QD emission wavelength. In the MZI, SAWs imprint a time-dependent optical phase and modulate the qubit rotation to the output superposition state. This enables dynamic single photon routing with frequencies exceeding one gigahertz. Finally, the combination of the dynamic single photon control and spectral tuning of the QD realizes wavelength multiplexing of the input photon state and demultiplexing it at the output. Our approach is scalable to multi-component integrated quantum photonic circuits and is compatible with hybrid photonic architectures and other key components for instance photonic resonators or on-chip detectors