Center for Advanced Photonics and Electronics

Cambridge, United Kingdom

Center for Advanced Photonics and Electronics

Cambridge, United Kingdom

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News Article | October 26, 2016
Site: www.eurekalert.org

Due to the nature of this work, it is hoped that such results will contribute to the field of correlated electronic glassy dynamics in condensed matter physics; give a better understanding of charge noise effects in mesoscopic devices; and enable new studies for developing novel technologies in the important field of semiconductor-based quantum information processing. Defect states acting as electron traps in oxide-semiconductor interfaces usually are sources of noise and tend to reduce the performance of nanoscale devices. Such defect states can modify the electrostatic environment experienced by conducting electrons, forcing them to percolate through nanowire-like pathways at low enough temperatures. This effectively allows a detection mechanism of the occupation of such trap sites by the current measured in the conduction channel. Such effect is normally observed as random telegraph noise (RTN), which corresponds to the incoherent emission and capture of electrons in the trap states, mediated by the thermal background. Motivated by the big changes in the conductivity caused by RTN in field-effect transistors (FET), scientists at the Quantum Nanoelectronics Research Center, Institute of Innovative Research (Tokyo Tech), the Center for Advanced Photonics and Electronics (University of Cambridge), and Cavendish Laboratory (University of Cambridge) investigated possible mechanisms in which the occupation of defects states could be both observed and dynamically mediated by means of coherent microwave fields. Working at cryogenic temperatures, it was found that the dynamics of such trap states are consistent with two-level systems (TLS), in which the energy levels are discrete and only the two lowest are accessible within the energy of the excitation signal. A TLS can represent the basis for a quantum bit implementation. From the microwave spectroscopic signature of the response of the FET used in this work, displaying a great number of high-quality factor resonances (Q > 10000), the extracted coherence times observed in this study are considerably longer, by almost three orders of magnitude, than other defect-based implementations of TLS. Performing single-pulse experiments gives the possibility to study the dynamics of the trapped electrons, which have been found not to depend on the chemistry of the dielectric used. And using a standard Ramsey protocol, coherent control was achieved. Furthermore, employing an optical master equation that captures the dynamics of the trapped electrons and a physical model based on linear response theory, it was possible to reproduce the experimental behavior observed in the experiments. Furthermore, it was found that the defect states are relatively well protected against phonons, explaining the long decoherence times measured, and that the main source of back-action could be related to long-range Coulombic interactions with other charges. Finally, since each resonance can be addressed independently in frequency space, the wide distribution of long coherence times observed, and the quasi-uniform density of states measured, it is hoped that this work could motivate the possibility to use such systems as quantum memories or quantum bits in future quantum information processing implementations.


Zhu J.,China Electric Power Research Institute | Cheng Q.,Beijing Jiaotong University | Yang B.,Beijing Jiaotong University | Yuan W.,Center for Advanced Photonics and Electronics | And 2 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

A high temperature superconducting magnetic energy storage system (HT-SMES) is constructed using YBCO coated conductor and is integrated with a cryogenic system using sub-cooled LN2. A closed loop control algorithm, based on the digital signal processor (DSP) TMS320F2812, is proposed using the 2G HT-SMES to compensate dynamic voltage sag in power systems. A dynamic simulation experiment for compensation of instantaneous voltage sag is achieved. The experiment circuit is built using a signal conditioning circuit, a DSP controlling circuit, a power conversion circuit and a SMES unit. Analysis of the voltage waveforms before and after compensation validates that this SMES system is able to compensate instantaneous voltage sag. © 2010 IEEE.


Yuan W.,Center for Advanced Photonics and Electronics | Ainslie M.D.,Center for Advanced Photonics and Electronics | Xian W.,Center for Advanced Photonics and Electronics | Hong Z.,Center for Advanced Photonics and Electronics | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2011

This paper begins with introducing the winding techniques of two superconducting double-pancake coils wound using 2G coated conductors. These winding techniques are able to guarantee a good performance for the superconducting coils. Then the coil critical currents were measured and compared with a simulation model. The results were consistent. Finally the coil AC losses were measured using an experimental circuit including a compensation coil. The simulation results are close to the experiment results. © 2010 IEEE.


Yuan W.,Center for Advanced Photonics and Electronics | Xian W.,Center for Advanced Photonics and Electronics | Ainslie M.,Center for Advanced Photonics and Electronics | Hong Z.,Center for Advanced Photonics and Electronics | And 4 more authors.
IEEE Transactions on Applied Superconductivity | Year: 2010

This paper presents an SMES coil which has been designed and tested by University of Cambridge. The design gives the maximum stored energy in the coil which has been wound by a certain length of second-generation high-temperature superconductors (2G HTS). A numerical model has been developed to analyse the current density and magnetic field distribution and calculate the AC losses during the charge and discharge process of the coil. A cryostat has been designed and a test of the I-V curve measurement of the coil has been accomplished. In addition, the power electronics control of the SMES coil has been simulated. © 2006 IEEE.


Amaratunga G.,Center for Advanced Photonics and Electronics
Proceedings - 2010 8th International Vacuum Electron Sources Conference and Nanocarbon, IVESC 2010 and NANOcarbon 2010 | Year: 2010

Current work on using nanostructured carbon surfaces in supercapacitors and batteries to enable enhanced performance is discussed. The emphasis is on solid electrolyte based batteries and supercapacitors which can be flexible and change form factor. This is a new concept for energy storage systems driven by the requirements of next generation mobile communication devices which will be designed to supplement regular battery power with power from harvested energy. It will be shown that a new class of flexible supercapacitors and batteries can be realised through use of carbon electrodes with enhanced nanostructure. © 2010 IEEE.

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