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PhD Researcher, The University of Sheffield


Electro-mechanical systems are very promising for tuning of quantum devices on a photonic chip

Quantum computers could revolutionise our technology-reliant world with their superior speed, efficiency and security compared to classical computers. However, quantum technologies still remain in various development stages in specialist research groups (like mine) around the world. A classical computer uses electrons to transfer information around the circuit, transistors to perform computing operations on them, and capacitors to store the information as either 0 or 1 in the form of classical bits. A quantum computer uses quantum bits (qubits), which, contrary to classical bits, can represent any number between 0 and 1 simultaneously, enabling parallel computing. A qubit needs to be a quantum two-level system to meet the requirement of being in a superposition of two states (0 and 1). One of the most favourable physical implementations of a qubit is a Quantum Dot (QD). A QD is a semiconductor nanostructure that confines the mobile carriers of charge (electrons and holes) in all three spatial dimensions, which thus results in the energy levels of the carriers being quantized. If engineered properly they emit single photons to transfer the information around the circuit. Computing processes can then be performed on photons using linear optics. Hence, all the essential components of classical computers have to be re-invented for optical circuits. My research focuses on designing, modelling and testing novel photonic devices with embedded QDs for quantum information processing applications.

An example of a necessary computing element is a switch, which is utilized in a classical computer with a transistor. A photonic switch can be realised using a beam splitter made of two waveguides if the distance between them can be controlled in-situ. As the distance is varied the light splits differently between the two waveguides as the evanescent light coupling changes. Micro-opto-electro-mechanical systems (MOEMS) are one of the most promising emerging approaches that can provide such control. Parts of MOEMS are made to deflect mechanically when voltage is applied between terminals. This allows to change the distance between the two waveguides and, if enough control is achieved, to make a photonic switch. Recently, my group has demonstrated this concept experimentally with embedded QDs for the first time. MOEMS are very versatile and can be adapted to control many other essential devices that will bring us closer to a realisation of the first quantum optical circuit.


Micromachines, Vol. 7, Pages 188: Electrostatic Comb-Drive Actuator with High In-Plane Translational Velocity

Abstract: This work reports the design and opto-mechanical characterization of high velocity comb-drive actuators producing in-plane motion and fabricated using the technology of deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrate. The actuators drive vertical mirrors acting on optical beams propagating in-plane with respect to the substrate. The actuator-mirror device is a fabrication on an SOI wafer with 80 μm etching depth, surface roughness of about 15 nm peak to valley and etching verticality that is better than 0.1 degree. The travel range of the actuators is extracted using an optical method based on optical cavity response and accounting for the diffraction effect. One design achieves a travel range of approximately 9.1 µm at a resonance frequency of approximately 26.1 kHz, while the second design achieves about 2 µm at 93.5 kHz. The two specific designs reported achieve peak velocities of about 1.48 and 1.18 m/s, respectively, which is the highest product of the travel range and frequency for an in-plane microelectromechanical system (MEMS) motion under atmospheric pressure, to the best of the authors’ knowledge. The first design possesses high spring linearity over its travel range with about 350 ppm change in the resonance frequency, while the second design achieves higher resonance frequency on the expense of linearity. The theoretical predications and the experimental results show good agreement.

Pub.: 17 Oct '16, Pinned: 27 Nov '17

A novel triangular-electrode based capacitive sensing method for MEMS resonant devices

Abstract: This paper reports a novel capacitive sensing method, enabling accurate and self-calibrated measurements for both the amplitude and phase information in sinusoidal motion. The approach constructively utilizes the inherent nonlinearity of a triangular-electrode based (TEB) variable-area sense capacitor. In the case of TEB detection signal, two harmonics exist and each carries information about the motional amplitude and phase. The TEB method robustly extracts the motional amplitude from the ratio of two sideband amplitudes and extracts the motional phase from the subtraction of two sideband phases. This technique is especially valuable for capacitive detection of periodic motion in MEMS resonant devices, such as the resonant accelerometer and Coriolis vibratory gyroscope. The paper presents detailed theoretical analysis and proposes a real-time measurement algorithm implemented in an FPGA device. Experimental results manifest that, compared with the traditional linear method, the sensitivity of the measured amplitude and phase to system parameter variations is highly suppressed up to 95%. Furthermore, an oscillation control system with TEB capacitive detection is introduced for micro-machined vibratory gyroscopes. First measurement results show the amplitude variance of the drive displacement is 120 ppm in an hour while the phase variance is 80 ppm. Allan variance analysis indicates a bias instability of 6.5°/hr for the gyroscope output.

Pub.: 29 Oct '16, Pinned: 27 Nov '17