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Practical pulse engineering： Gradient ascent without matrix exponentiation

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Frontiers of physics 2018年第3期13卷 3-8页

作者： Gaurav Bhole Jonathan A. Jones Centre for Quantum Computation Clarendon Laboratory University of Oxford Parks Road OX1 3PU UK

Since 2005, there has been a huge growth in the use of engineered control pulses to perform desired quantum operations in systems such as nuclear magnetic resonance quantum information processors. These approaches, which build on the original gradient ascent pulse engineering algorithm, remain computationally intensive because of the need to calculate matrix exponentials for each time step in the control pulse. In this study, we discuss how the propagators for each time step can be approximated using the Trotter-Suzuki formula, and a further speedup achieved by avoiding unnecessary operations. The resulting procedure can provide substantial speed gain with negligible costs in the propagator error, providing a more practical approach to pulse en-ineerinK.

关键词： quantum information coherent control pulse sequences in nuclear magnetic resonance

Fracture Mechanics,Crack Propagation and Microhardness Studies on Flux Grown ErAlO_3 Single Crystals

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Journal of Materials Science & Technology 2000年第4期16卷 405-410页

作者： K.K.Bamzai and P.N.Kotru (Department of Physics, University of Jammu, Jammu 180006, India) B.M Wanklyn (Department of Physics, clarendon laboratory, Oxford University, Oxford OX1 3PU, U.K.) Department of Physics University of Jammu Jammu 180006 India Department of Physics Clarendon Laboratory Oxford University Oxford OX1 3PU United Kingdom

Results on fracture mechanics and crack propagation have been obtained, making use of Vickers microhardness studies on two different crystallographic planes [(110) and (001)] of flux grown erbium aluminate crystals in the load ranging from 10-100 g. The variation of microhardness with load which is best explained by Hays and Kendall's law leads to the load independent values of hardness. Classification of cracks is dealt with and it is reported that the transition from Palmqvist to median types of cracks occurs at higher loads. The values of fracture toughness (K_C), and brittleness index (B_i) are calculated using median types of cracks.

关键词： Fracture Mechanics Crack Propagation and Microhardness Studies on Flux Grown ErAlO3 Single Crystals

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An introduction to dressed-atom adiabatic potentials for ultracold atoms

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Instrumentation 2015年第4期2卷 76-84页

作者： Tiffany Harte Elliot Bentine Edward Owen XU Dongyang Benjamin Yuen Christopher Foot clarendon laboratory University of Oxford

We give a simple introduction to the theoretical treatment of atoms interacting strongly w ith electromagnetic fields in the radiofrequency,microw ave and laser domains. In particular,w e discuss the concept of dressed atoms,w hich considers the combination of the atom and photons as a composite physical system. This pow erful concept has a w ide range of applications in atomic physics and w e give a few examples of its use in the manipulation of ultracold atoms in adiabatic potentials. These examples are selected from experimental w ork conducted by our research team in Oxford but there are numerous other applications and w e outline some future possibilities.

关键词： Ultracold atoms dressed potentials

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Enhanced photoluminescence quantum yield of MAPbBr3 nanocrystals by passivation using graphene

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Nano Research 2020年第4期13卷 932-938页

作者： Youngsin Park Atanu Jana Chang Woo Myung Taeseung Yoon Geungsik Lee Claudius C.Kocher Guanhua Ying Vitaly Osokin Robert A.Taylor Kwang S.Kim School of Natural Science Ulsart National Institute of Science and TechnologhUlsan 44919Republic of Korea 2 Clarendon LaboratoryDepartment of PhysicsUniversity of OxfordParks RoadOxford0X13PUUK

Diminishing surface defect states in perovskite nancx^rystals is a highly challenging subject for enhancing optoelectronic device *** synthesized organic/inorganic lead-halide perovskite MAPbBr3(MA=methylammonium)clusters comprising nanocrystals with diameters ranging between 20 and 30 nm and characterized an enhanced photoluminescence(PL)quantum yield(as much as^7 times)by encapsulating the MAPbBr3 with graphene(Gr).The optical properties of MAPbBr3 and Gr/MAPbBr3 were investigated by temperature-dependent micro-PL and time-resolved PL *** functional theory calculations show that the surface defect states in MAPbBr3 are removed and the optical band gap is reduced by a 0.15 eV by encapsulation with graphene due to partial restoration of lattice distortions.

关键词： perovskite nanocluster photoluminescence surface passivation graphene density functional theory calculations

ARPES investigation of the electronic structure and its evolution in magnetic topological insulator MnBi2+2nTe4+3n family

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National Science Review 2024年第2期11卷 81-93页

作者： Runzhe Xu Lixuan Xu Zhongkai Liu Lexian Yang Yulin Chen State Key laboratory of Low Dimensional Quantum Physics Department of PhysicsTsinghua University School of Physical Science and Technology Shanghai Tech University and CAS-Shanghai Science Research Center Shanghai Tech laboratory for Topological Physics Frontier Science Center for Quantum Information Collaborative Innovation Center of Quantum Matter Department of Physics Clarendon LaboratoryUniversity of Oxford

In the past 5 years,there has been significant research interest in the intrinsic magnetic topological insulator family compounds MnBi2+2nTe4+3n（where n=0,1,2…）.In particular,exfoliated thin films of MnBi2Te4have led to numerous experimental breakthroughs,such as the quantum anomalous Hall effect,axion insulator phase and high-Chern number quantum Hall effect without Landau ***,despite extensive efforts,the energy gap of the topological surface states due to exchange magnetic coupling,which is a key feature of the characteristic band structure of the system,remains experimentally *** electronic structure measured by using angle-resolved photoemission （ARPES） shows significant deviation from ab initio prediction and scanning tunneling spectroscopy measurements,making it challenging to understand the transport results based on the electronic *** paper reviews the measurements of the band structure of MnBi2+2nTe4+3nmagnetic topological insulators using ARPES,focusing on the evolution of their electronic structures with temperature,surface and bulk doping and film *** aim of the review is to construct a unified picture of the electronic structure of MnBi2+2nTe4+3ncompounds and explore possible control of their topological properties.

关键词： magnetic topological insulator MnBi2Te4 electronic structure angle-resolved photoemission spectroscopy

Quantum Oscillations in Noncentrosymmetric Weyl Semimetal SmAlSi

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Chinese Physics Letters 2022年第4期39卷 67-73页

作者： Weizheng Cao Yunlong Su Qi Wang Cuiying Pei Lingling Gao Yi Zhao Changhua Li Na Yu Jinghui Wang Zhongkai Liu Yulin Chen Gang Li Jun Li Yanpeng Qi School of Physical Science and Technology ShanghaiTech UniversityShanghai 201210China ShanghaiTech laboratory for Topological Physics ShanghaiTech UniversityShanghai 201210China Department of Physics Clarendon LaboratoryUniversity of OxfordParks RoadOxford OX13PUUK Shanghai Key laboratory of High-resolution Electron Microscopy ShanghaiTech UniversityShanghai 201210China

As a new type of quantum state of matter hosting low energy relativistic quasiparticles,Weyl semimetals(WSMs)have attracted significant attention for scientific community and potential quantum device *** this study,we present a comprehensive investigation of the structural,magnetic,and transport properties of noncentrosymmetric RAl Si(R=Sm,Ce),which have been predicted to be new magnetic WSM *** samples exhibit nonsaturated magnetoresistance,with about 900%and 80%for Sm Al Si and Ce Al Si,respectively,at temperature of 1.8 K and magnetic field of 9 *** carrier densities of Sm Al Si and Ce Al Si exhibit remarkable change around magnetic transition temperatures,signifying that the electronic states are sensitive to the magnetic ordering of rare-earth *** low temperatures,Sm Al Si reveals prominent Shubnikov–de Haas oscillations associated with the nontrivial Berry ***-pressure experiments demonstrate that the magnetic order is robust and survival under high *** results would yield valuable insights into WSM physics and potentials in applications to next-generation spintronic devices in the RAl Si(R=Sm,Ce)family.

关键词： symmetric quantum nontrivial

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Data-driven science and machine learning methods in laser–plasma physics

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High Power Laser Science and Engineering 2023年第5期 14-54页

作者： Andreas D?pp Christoph Eberle Sunny Howard Faran Irshad Jinpu Lin Matthew Streeter Ludwig-Maximilians-Universit?t München Department of Physics Clarendon Laboratory University of Oxford School for Mathematics and Physics Queen's University Belfast

Laser-plasma physics has developed rapidly over the past few decades as lasers have become both more powerful and more widely available. Early experimental and numerical research in this field was dominated by single-shot experiments with limited parameter exploration. However, recent technological improvements make it possible to gather data for hundreds or thousands of different settings in both experiments and simulations. This has sparked interest in using advanced techniques from mathematics, statistics and computer science to deal with, and benefit from, big data. At the same time, sophisticated modeling techniques also provide new ways for researchers to deal effectively with situation where still only sparse data are available. This paper aims to present an overview of relevant machine learning methods with focus on applicability to laser-plasma physics and its important sub-fields of laser-plasma acceleration and inertial confinement fusion.

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Gain enhancement of perovskite nanosheets by a patterned waveguide:excitation and temperature dependence of gain saturation

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Light(Science & Applications) 2023年第12期12卷 2688-2699页

作者： Inhong Kim Ga Eul Choi Ming Mei Min Woo Kim Minju Kim Young Woo Kwon Tae-In Jeong Seungchul Kim Suck Won Hong Kwangseuk Kyhm Robert A.Taylor Department of Opto&Cogno Mechatronics Engineering RCDAMPPusan National UniversityBusan 46241Republic of Korea Department of Nano-Fusion Technology Pusan National UniversityBusan 46241Republic of Korea clarendon laboratory Department of PhysicsUniversity of OxfordOxford OX13PUUK

Optical gain enhancement of two-dimensional CsPbBr3 nanosheets was studied when the amplified spontaneous emission is guided by a patterned structure of *** the uncertainties and pitfalls in retrieving a gain coefficient from the variable stripe length method,a gain contour g((h))ω.x)was obtained in the plane of spectrum energy(hω)and stripe length(x),whereby an average gain was obtained,and gain saturation was *** and temperature dependence of the gain contour show that the waveguide enhances both gain and thermal stability due to the increased optical confinement and heat dissipation,and the gain origins were attributed to the two-dimensional excitons and the localized states.

关键词： waveguide saturation contour

Coarse and fine-tuning of lasing transverse electromagnetic modes in coupled all-inorganic perovskite quantum dots

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Nano Research 2021年第1期14卷 108-113页

作者： Youngsin Park Guanhua Ying Atanu Jana Vitaly Osokin Claudius C.Kocher Tristan Farrow Robert A.Taylor Kwang S.Kim School of Natural Science Ulsan National Institute of Science and TechnologhUlsan 44919Republic of Korea clarendon laboratory Department of PhysicsUniversity of OxfordParks RoadOxford OX13PUUK Centre for Quantum Technologies National University of SingaporeScience Drive 2Singapore 117543Singapore

Inorganic perovskite lasers are of particular interest,with much recent work focusing on Fabry-P6rot cavity-forming *** demonstrate the direct observation of lasing from transverse electromagnetic(TEM)modes with a long coherence time-9.5ps in coupled CsPbBr_(3) quantum dots,which dispense with an external cavity resonator and show how the wavelength of the modes can be controlled via two independent *** the pump power allowed us tofine-tune the TEM mode structure to the emission wavelength,thus providing a degree of control over the properties of the lasing *** temperature-tuning provided an additional degree of control over the wavelength of the lasing peak,importantly,maintained a constant full width at half maximum(FWHM)over the entire tuning range without mode-hopping.

关键词： perovskite quantum dots coherent lasing transverse electromagnetic mode stimulated emission