43 research outputs found
RF circuit and antenna optimization using space mapping technique
No full textThe use of EM simulation in circuit optimization in RF domain is very common. There are some problems with this kind of optimization. Firstly, in many cases EM simulations are expensive process. Another problem is the relationship between circuit response and design variable is not an easy function in many cases.
In order to overcome these problems a technique named space mapping (SM) was suggested. This technique has been experimentally proved as effective and efficient technique to do optimization including RF circuit optimization.
From large number of SM algorithm variants there are only a few that are designed specially for constrained optimization. In this report some constrained SM algorithms using projection method are investigated. These algorithms are variants of Aggressive Space Mapping (ASM) and Aggressive Output Space Mapping (AOSM) and designed to handle convex constraints. The methods are used to optimize multilayer LTCC bandpass filter. The numerical results shows good convergence rate.
All of the constrained SM algorithms designed in this report use equivalent circuit and embedded knowledge in coarse model. Parameter extraction is done using circuit tuning based on physical augmentation. In order to test the efficiency of the tuning method, this tuning method is used to tune multilayer LTCC bandpass filter equivalent circuit. The result shows this tuning algorithm is effective and efficient.
This circuit tuning algorithm is a derivative of a modeling algorithm based on physical augmentation. The use of this modeling technique in producing equivalent circuit for antenna is investigated. It is shown experimentally that this modeling algorithm is effective and efficient.
Although some of proposed constrained SM algorithms are designed to provide global convergence, the author can not prove the global convergence mathematically. The author can only provide the proof for local convergence of some constrained SM algorithms. Further developments may be done in the direction of finding the mathematical analysis of these SM algorithms, refining the methods especially the AOSM based methods and combining the ASM and AOSM.Bachelor of Engineerin
Room temperature nanocavity laser with interlayer excitons in 2D heterostructures
No full textAtomically thin layered two-dimensional (2D) materials have provided a rich library for both fundamental research and device applications. Bandgap engineering and controlled material response can be achieved from artificial heterostructures. Recently, excitonic lasers have been reported using transition metal dichalcogenides; however, the emission is still the intrinsic energy bandgap of the monolayers. Here, we report a room temperature interlayer exciton laser with MoS2/WSe2 heterostructures. The onset of lasing was identified by the distinct kink in the “L-L” curve and the noticeable spectral linewidth collapse. Different from visible emission of intralayer excitons in monolayer components, our laserworks in the infrared range, which is fully compatible with the well-established technologies in silicon photonics. Long lifetime of interlayer excitons relaxes the requirement of the cavity quality factor by orders of magnitude. Room temperature interlayer exciton lasers might open new perspectives for developing coherent light sources with tailored optical properties on silicon photonics platforms
Accessos directes a adiabaticity per al transport de les ones de matèria
No full textTreball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat
Accessos directes a adiabaticity per al transport de les ones de matèria
No full textTreball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat
Light-matter interaction in 2D transition metal dichalcogenide heterostructure : magneto photoluminescence, lasing, and photocurrent
No full textThe two-dimensional (2D) transition metal dichalcogenide (TMD) features many properties that are desirable for applications in spintronics and valleytronics, as well as in excitonic devices, all of which aims for more energy-efficient devices. Moreover, even richer physical phenomena involving interlayer interaction can be observed when two TMD monolayers are stacked together creating, the 2D TMD heterostructure.
This thesis presents the study of several aspects of the interaction between matter and light in the two-dimensional TMD heterostructure. First, the study regarding the MoSe2/WSe2 interlayer exciton dynamics under circularly polarized excitation and magnetic field influence is presented. We show that the interlayer exciton dynamic is affected by the dark WSe2 exciton. Moreover, we found that the interlayer exciton transition energy corresponding to maximum transition strength depends on the excitation polarization indicating a large optically induced pseudomagnetic field.
Next, the study of the interaction between the MoS2/WSe2 interlayer exciton with light inside a cavity is presented. We show that the long interlayer exciton lifetime enables an excitonic laser with ultralow threshold power even with a low Q-factor cavity.
Lastly, we show that the circular photogalvanic effect (CPGE) can be generated at the boundary between the 2D MoS2/WSe2 heterostructure and a metal electrode. The observed CPGE is due to the valley-dependent shift of the valence band induced by the combination of the built-in electric field and the optical selection rule of the valley as well as the different effective relaxation times between electron and hole in the 2D heterostructure.
The findings presented in this thesis may be useful for realizing opto-valleytronics, opto-spintronics, as well as excitonic device applications which is based on 2D TMD heterostructure as a platform. We discuss several possible future research directions based on these findings.Doctor of Philosoph
Accessos directes a adiabaticity per al transport de les ones de matèria
No full textTreball final de màster oficial fet en col·laboració amb Universitat Autònoma de Barcelona (UAB), Universitat de Barcelona (UB) i Institut de Ciències Fotòniques (ICFO)[ANGLES] In this master thesis we investigate the quantum transport of a single neutral atom between double-well and triple-well potentials. In particular, we study and implement the Fast-Forward technique to speed up the quantum dynamics of the Three-Level Atom Optics (TLAO) based transport. We show that the resulting technique is faster and, against certain experimentaimperfections, more robust than the usual TLAO-based transport. Moreover, we address different shortcuts to adiabaticity examples. First, we derive a more general shortcut to adiabaticity for adiabatic translation than the one reported in the literature. Also, we obtain a criterion for the realization of a shortcut to adiabaticity and we show that, under this criterion, it is impossible to derive a realizable shortcut to adiabaticity using the Fast-Forward technique for the TLAO-based transport.[CASTELLÀ] Esta tesis de maestría se investiga el transporte cuántico de un átomo neutro entre los potenciales de doble-well y triple-well. En particular, estudiamos y aplicamos la técnica de Fast-Forward para acelerar la dinámica cuántica de la Three-Level Atom Optics (TLAO) transporte basado. Se demuestra que la técnica es que resulta más rápido y, en contra de ciertas imperfecciones experimentales, más robusto que el transporte TLAO basado habitual. Por otra parte, abordamos diferentes accesos directos a ejemplos adiabaticity. En primer lugar, derivamos un acceso más general a adiabaticity para su traducción adiabática que la reportada en la literatura. Además, se obtiene un criterio para la realización de un acceso directo a adiabaticity y mostramos que, bajo este criterio, no se puede derivar un acceso directo a adiabaticity realizable mediante la técnica de Fast-Forward para el transporte TLAO basado.[CATALA] En aquesta tesi de mestratge s'investiga el transport quàntic d'un àtom neutre entre els potencials de doble-well i triple-well. En particular, estudiem i apliquem la tècnica de Fast-Forward per accelerar la dinàmica quàntica de la Three-Level Atom Optics (TLAO) transport basat. Es demostra que la tècnica és que resulta més ràpid i, en contra de certes imperfeccions experimentals, més robust que el transport TLAO basat habitual. D'altra banda, abordem diferents accessos directes a exemples adiabaticity. En primer lloc, derivem un accés més general adiabaticity per a la seva traducció adiabàtica que la considerada en la literatura. A més, s'obté un criteri per a la realització d'un accés directe a adiabaticity i mostrem que, sota aquest criteri, no es pot derivar un accés directe a adiabaticity realitzable mitjançant la tècnica de Fast-Forward per al transport TLAO basat
Opto-valleytronics in the 2D van der Waals heterostructure
No full textThe development of information processing device with minimum carbon emission is crucial in this information age. One of the approaches to tackle this challenge is by using valleys (local extremum points in the momentum space) to encode the information instead of charges. The valley information in some material such as monolayer transition metal dichalcogenide (TMD) can be controlled by using circularly polarized light. This opens a new field called opto-valleytronics. In this article, we first review the valley physics in monolayer TMD and 2D heterostructure composed of monolayer TMD and other materials. Such 2D heterostructure has been shown to exhibit interesting phenomena such as interlayer exciton, magnetic proximity effect, and spin-oTbit proximity effect, which is beneficial for opto-valleytronics application. We then review some of the optical valley control methods that have been used in the monolayer TMD and the 2D heterostructure. Finally, a summary and outlook of the 2D heterostructure opto-valleytronics are given.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionWe acknowledge the financial support from the Singapore National Research Foundation through its Competitive Research Program (CRP Award No. NRF-CRP21-2018-0007), Singapore Ministry of Education (MOE2016-T2-2-077, MOE2016-T2-1-163 and MOE2016-T3-1-006 (S)), A*Star QTE programme
Modified constrained explicit knowledge-embedded space mapping using circuit tuning based on physical augmentation as parameter extraction
No full text10.1002/mmce.20583International Journal of RF and Microwave Computer-Aided Engineering22149-58IJME
Optical signature of cascade transitions between moir\'e interlayer excitons
No full textCascade transition between energy levels has important applications, such as
in quantum information protocols and quantum cascade lasers. In two-dimensional
heterostructure, the moir\'e superlattice potential can result in multiple
interlayer exciton (IX) energy levels. We demonstrate the cascade transitions
between such moir\'e IXs by performing time- and energy-resolved
photoluminescence measurements. We show that the lower-energy moir\'e IX can be
excited to higher-energy ones, facilitating IX population inversion
Coherent control of a strongly driven silicon vacancy optical transition in diamond
No full text© 2017 The Author(s). The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid-state emitters have emerged as promising candidates with their prospects for on-chip integration as quantum nodes and sources of coherent photons connecting these nodes. Under a strongly driving resonant laser field, such quantum emitters can exhibit quantum behaviour such as Autler-Townes splitting and the Mollow triplet spectrum. Here we demonstrate coherent control of a strongly driven optical transition in silicon vacancy centre in diamond. Rapid optical detection of photons enabled the observation of time-resolved coherent Rabi oscillations and the Mollow triplet spectrum. Detection with a probing transition further confirmed Autler-Townes splitting generated by a strong laser field. The coherence time of the emitted photons is comparable to its lifetime and robust under a very strong driving field, which is promising for the generation of indistinguishable photons
