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Effects of inter-subband couplings on bound and extended states of terahertz cascade structures
摘要： We theoretically analyze the effect of inter-subband couplings on the eigenstates of a terahertz heterostructure in the presence of coulombic donors. We find that the inter-subband electron-donor interaction causes a drastic reorganization of the eigenenergies and a strong admixture between the subbands that decisively influences the optical absorption spectrum of the structure. These results illustrate the importance of the inter-subband couplings in the formulation of the eigenstates of imperfect terahertz heterostructures.
关键词： inter-subband couplings,eigenstates,terahertz cascade structures,optical absorption spectrum
更新于2025-09-23 15:21:21
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Efficient Orthogonal Control of Tunnel Couplings in a Quantum Dot Array
摘要： Electrostatically-defined semiconductor quantum dot arrays offer a promising platform for quantum computation and quantum simulation. However, crosstalk of gate voltages to dot potentials and interdot tunnel couplings complicates the tuning of the device parameters. To date, crosstalk to the dot potentials is routinely and efficiently compensated using so-called virtual gates, which are specific linear combinations of physical gate voltages. However, due to exponential dependence of tunnel couplings on gate voltages, crosstalk to the tunnel barriers is currently compensated through a slow iterative process. In this work, we show that the crosstalk on tunnel barriers can be efficiently characterized and compensated for, using the fact that the same exponential dependence applies to all gates. We demonstrate efficient calibration of crosstalk in a quadruple quantum dot array and define a set of virtual barrier gates, with which we show orthogonal control of all interdot tunnel couplings. Our method marks a key step forward in the scalability of the tuning process of large-scale quantum dot arrays.
关键词： quantum simulation,quantum dot arrays,tunnel couplings,quantum computation,crosstalk compensation
更新于2025-09-23 15:21:01
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Waveguide-induced coalescence of exceptional points
摘要： In non-Hermitian systems, multiple eigenstates can merge into one state at so-called exceptional points (EPs). This paper presents the coalescence of the multiple EPs based on a waveguide. For the ring cavities located at the second-order EPs with desired chiral modes, the waveguide provides unidirectional couplings among the modes of the second-order EPs, which merges the second-order EPs into one high-order EP. The principle of this framework and properties of this system are presented by analyzing the effective Hamiltonian of the system, a mode-coupling diagram, and numerical simulations.
关键词： unidirectional couplings,exceptional points,high-order EP,non-Hermitian systems,waveguide
更新于2025-09-23 15:21:01
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Computer-automated tuning procedures for semiconductor quantum dot arrays
摘要： As with any quantum computing platform, semiconductor quantum dot devices require sophisticated hardware and controls for operation. The increasing complexity of quantum dot devices necessitates the advancement of automated control software and image recognition techniques for rapidly evaluating charge stability diagrams. We use an image analysis toolbox developed in Python to automate the calibration of virtual gates, a process that previously involved a large amount of user intervention. Moreover, we show that straightforward feedback protocols can be used to simultaneously tune multiple tunnel couplings in a triple quantum dot in a computer automated fashion. Finally, we adopt the use of a “tunnel coupling lever arm” to model the interdot barrier gate response and discuss how it can be used to more rapidly tune interdot tunnel couplings to the gigahertz values that are compatible with exchange gates.
关键词： image recognition,tunnel couplings,automated control software,virtual gates,semiconductor quantum dot devices,charge stability diagrams,quantum computing
更新于2025-09-11 14:15:04
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Beyond Born-Oppenheimer treatment on spectroscopic and scattering processes
摘要： We review the formulation of beyond Born-Oppenheimer (BBO) theory based on first principle for the construction of diabatic potential energy surfaces (PESs) both for few important spectroscopic systems, viz., Na3 cluster, NO2 radical as well as scattering process like D+ + H2. The essential theoretical development leading to the BBO equations are thoroughly discussed. It has been found that the above molecular systems posses numerous nonadiabatic interactions that range from Jahn-Teller, Renner-Teller types of conical intersections along with strong pseudo Jahn-Teller couplings between various electronic states. We have calculated the adiabatic PESs and nonadiabatic coupling terms for those systems and subsequently performed adiabatic-to-diabatic transformation to construct smooth, symmetric and continuous diabatic potential energy matrix. Nuclear dynamics has been performed on the diabatic PESs of Na3 and NO2 to simulate the photoelectron spectra that match quite well with the experimentally measured ones. Moreover, we have carried out reactive scattering dynamics on the adiabatic and diabatic surfaces of H+3 system to reproduce experimental cross sections for reactive charge and non-charge transfer processes.
关键词： Beyond Born-Oppenheimer theory,nuclear dynamics,photoelectron spectra,reactive scattering dynamics,conical intersections,Jahn-Teller,diabatic potential energy surfaces,Renner-Teller,nonadiabatic interactions,pseudo Jahn-Teller couplings
更新于2025-09-09 09:28:46
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Synthesis, structural characterization and photophysical properties of 7-cyanohexahelicene
摘要： 7-Cyanoexahelicene has been prepared in racemic form through a short photochemical synthetic approach and its enantiomeric separation was studied and allowed to obtain (P)- and (M)-enantiomers in 100% ee and > 98.5% ee, respectively. The optical rotatory dispersion and electronic circular dichroism (ECD) spectra of the resolved ones were measured. Other optical properties such as UV and photoluminescence as well as the electrochemical behavior were also examined in solutions.
关键词： Optical resolution,Chirality,Couplings,Photophysical properties,gap energy,Helicenes,Photooxidation
更新于2025-09-04 15:30:14
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[Advances In Atomic, Molecular, and Optical Physics] Volume 67 || Radio-Frequency Spectroscopy as a Tool for Studying Coherent Spin Dynamics and for Application to Radio-Frequency Magnetometry
摘要： The technique of radio-frequency spectroscopy was introduced more than 50 years ago, but is continuing to evolve and is being used as an ever-more versatile tool. We describe the underlying processes that govern the various contributions to the spectroscopic signals, considering the atom-light couplings. We then apply this understanding to demonstrate how the coherent dynamics can be manipulated with different configurations of optical pumping. Finally, we discuss how to implement rf spectroscopy to give optimized sensitivity in atomic magnetometers.
关键词： radio-frequency spectroscopy,atom-light couplings,atomic magnetometry,optical pumping,coherent spin dynamics
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Design of Ultra-Wideband Bandpass (UWB) Filter with Enhanced Couplings by Using Lumped Capacitors
摘要： This paper presents a novel ultra-wideband bandpass (UWB) filter with enhanced input/output couplings by high quality lumped capacitors in place of traditional coupling methods. The filter consists of traditional stub-loaded dual-mode resonator and a pair of lumped capacitors, which symmetrically located at the input/output ports. Different from the technology of parallel-coupled microstrip lines in enhancing the capacitive couplings, this paper uses high quality ceramics trimmer capacitors to realize strong capacitive couplings at the input/output ports. A compact microstrip UWB filter designed by this method is simulated, fabricated and measured. The simulated and measured results are in good agreements, showing validity of the proposed method.
关键词： dual-mode resonator,capacitive couplings,lumped capacitors,Ultra-wideband (UWB) filter
更新于2025-09-04 15:30:14