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$${\mathscr{P}}{\mathscr{T}}$$PT-symmetric interference transistor
摘要： We present a model of the molecular transistor, operation of which is based on the interplay between two physical mechanisms, peculiar to open quantum systems that act in concert: PT-symmetry breaking corresponding to coalescence of resonances at the exceptional point of the molecule, connected to the leads, and Fano-Feshbach antiresonance. This switching mechanism can be realised in particular in a special class of molecules with degenerate energy levels, e.g. diradicals, which possess mirror symmetry. At zero gate voltage infinitesimally small interaction of the molecule with the leads breaks the PT-symmetry of the system that, however, can be restored by application of the gate voltage preserving the mirror symmetry. PT-symmetry broken state at zero gate voltage with minimal transmission corresponds to the “off” state while the PT-symmetric state at non-zero gate voltage with maximum transmission – to the “on” state. At zero gate voltage energy of the antiresonance coincides with exceptional point. We construct a model of an all-electrical molecular switch based on such transistors acting as a conventional CMOS inverter and show that essentially lower power consumption and switching energy can be achieved, compared to the CMOS analogues.
关键词： diradicals,molecular transistor,CMOS inverter,quantum systems,PT-symmetric interference,Fano-Feshbach antiresonance
更新于2025-09-23 15:21:21
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Finite-time Stückelberg interferometry with nanomechanical modes
摘要： Stückelberg interferometry describes the interference of two strongly coupled modes during a double passage through an avoided energy level crossing. In this work, we investigate finite-time effects in Stückelberg interferometry and discuss the exact analytical solution of the double passage Stückelberg problem by expanding the finite-time solution of the Landau–Zener problem. Approximating the return probability amplitudes of the double passage in distinct limits reveals uncharted parameter regimes of Stückelberg interferometry where finite-time effects affect the coherent exchange of energy. We find the long-time limit of the exact solution to formally coincide with the well-established adiabatic impulse model which is, to the best of our knowledge, the only regime of Stückelberg interferometry reported so far. Experimentally, we study all predicted regimes using a purely classical, strongly coupled nanomechanical two-mode system of high quality factor. The classical two-mode system consists of the in-plane and out-of-plane fundamental flexural mode of a high stress silicon nitride string resonator, coupled via electric gradient fields. We exploit our experimental and theoretical findings by studying the onset of Stückelberg interference in dependence of the characteristic system control parameters and obtain characteristic excitation oscillations between the two modes even without the explicit need of traversing the avoided crossing. The presented findings are not limited to classical mechanical two-mode systems but can be applied to every strongly coupled (quantum) two-level system, for example a spin-1/2 system or superconducting qubit.
关键词： strong coupling,nanoelectromechanical systems,finite times,Stückelberg interferometry
更新于2025-09-23 15:21:21
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Effective spin physics in two-dimensional cavity QED arrays
摘要： We investigate a strongly correlated system of light and matter in two-dimensional cavity arrays. We formulate a multimode Tavis–Cummings (TC) Hamiltonian for two-level atoms coupled to cavity modes and driven by an external laser ?eld which reduces to an effective spin Hamiltonian in the dispersive regime. In one-dimension we provide an exact analytical solution. In two-dimensions, we perform mean-?eld study and large scale quantum Monte Carlo simulations of both the TC and the effective spin models. We discuss the phase diagram and the parameter regime which gives rise to frustrated interactions between the spins. We provide a quantitative description of the phase transitions and correlation properties featured by the system and we discuss graph-theoretical properties of the ground states in terms of graph colourings using Pólya’s enumeration theorem.
关键词： cavity arrays,Jaynes–Cummings,Dicke,ground states of spin systems,Tavis–Cummings models,frustrated spin models,quantum Monte Carlo
更新于2025-09-23 15:21:21
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Buchwald-Hartwig Coupling at the Naphthalenediimide Core: Access to Dendritic, Panchromatic NIR Absorbers with Exceptionally Low Band Gap
摘要： The ?rst successful Buchwald?Hartwig reaction at the naphthalenediimide core is reported, leading to the coupling of diverse secondary aromatic amines including dendritic donors. The G1-dendrimer-based donor exhibit blackish color, providing access to black absorbing systems. λ onset values up to 1070 nm was achieved, which is the maximum from a single NDI sca?old. These dyes also manifest multielectron reservoir properties. A total of eight-redox states with a band gap of ～0.95 eV was accomplished.
关键词： dendritic donors,low band gap,black absorbing systems,Buchwald?Hartwig reaction,naphthalenediimide,multielectron reservoir properties,NIR absorbers
更新于2025-09-23 15:21:21
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Assessing carbon sequestration of silvopastoral tropical landscapes using optical remote sensing and field measurements
摘要： This research assesses the potential of using high-resolution optical RS data and traditional field inventory to estimate carbon stocks in silvopastoral systems. We compare field data in the Macas region of the Ecuadorian Amazon with high-resolution RS data. Aboveground estimates of carbon were calculated using the field data. Tree cover was obtained through segmentation analysis of RS data. Results show 45% of the area in the study region is covered by trees and the rest is either pasture or areas cleared for new pastures. Field data shows a statistically significant positive correlation with percentage canopy cover estimated by segmentation analysis (R = 0.52), compared to a lower correlation with RS measures of NDVI (R = 0.11). In this study the amount of carbon stored in aboveground biomass ranges from 20 T/ha to 28 T/ha. The study shows how to estimate landscape variability in carbon storage, moving up in scale from ecological transects to farms.
关键词： Silvopastoral systems,carbon,optical high-resolution data,ecosystem services
更新于2025-09-23 15:21:21
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Direct characterization of linear and quadratically nonlinear optical systems
摘要： A central task in quantum-information processing is to characterize quantum processes. In the realm of optical quantum-information processing, this amounts to characterizing the transformations of the mode creation and annihilation operators. This transformation is unitary for linear optical systems, whereas these yield the well-known Bogoliubov transformations for systems with Hamiltonians that are quadratic in the mode operators. In this paper, we propose a shot-noise limited scheme for characterizing both these kinds of evolutions by employing a modified Mach-Zehnder interferometer. In order to characterize a N -mode device, we require O(N 2) measurements. Although it suffices to use coherent states for the characterization of linear optical systems, we additionally require single photons to characterize quadratically nonlinear optical systems.
关键词： Bogoliubov transformations,Mach-Zehnder interferometer,optical systems,quantum-information processing,coherent states,single photons
更新于2025-09-23 15:21:21
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Nonradiative decay and absorption rates of quantum emitters embedded in metallic systems: Microscopic description and their determination from electronic transport
摘要： We investigate nonradiative decay and absorption rates of two-level quantum emitters embedded in a metal at low temperatures. We obtain the expressions for both nonradiative transition rates and identify a unique, experimentally accessible way to obtain both nonradiative transition rates via electronic transport in the host metallic system. Our findings not only provide a microscopic description of the nonradiative channels in metals, but they also allow one to identify, determine, and differentiate them from other decay channels, which is crucial to the understanding and controlling of the light-matter interactions at the nanoscale.
关键词： nonradiative decay,metallic systems,quantum emitters,electronic transport,absorption rates
更新于2025-09-23 15:21:21
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Low-frequency spectroscopy for quantum multilevel systems
摘要： A periodically driven quantum system with avoided level crossing experiences both nonadiabatic transitions and wave-function phase changes. These result in coherent interference fringes in the system’s occupation probabilities. For qubits, with repelling energy levels, such interference, named after Landau-Zener-Stückelberg-Majorana, displays arc-shaped resonance lines. In the case of a multilevel system with an avoided level crossing of the two lower levels, we demonstrate that the shape of the resonances can change from convex arcs to concave heart-shaped and harp-shaped resonance lines. Indeed, the whole energy spectrum determines the shape of such resonance fringes and this also provides insight into the slow-frequency system spectroscopy. As a particular example, we consider this for valley-orbit silicon quantum dots, which are important for the emerging field of valleytronics.
关键词： valley-orbit silicon quantum dots,valleytronics,low-frequency spectroscopy,quantum multilevel systems,Landau-Zener-Stückelberg-Majorana interference
更新于2025-09-23 15:21:21
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Avoided Crossing and sub-Fourier-sensitivity in Driven Quantum Systems
摘要： The response of a linear system to an external perturbation is governed by the Fourier limit, with the inverse of the interaction time constituting a lower limit for the system bandwidth. This does not hold for nonlinear systems, which can thus exhibit sub-Fourier-behavior. The present Letter identifies a mechanism for sub-Fourier-sensitivity in driven quantum systems, which relies on avoided crossing between Floquet states. Features up to three orders of magnitude finer than the Fourier limit are presented.
关键词： driven quantum systems,Floquet states,avoided crossing,sub-Fourier-sensitivity
更新于2025-09-23 15:21:21
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Real-Time MPPT Optimization of PV Systems by Means of DCD-RLS Based Identification
摘要： Maximum power point tracking (MPPT) algorithms continuously change duty cycle of a power converter to extract maximum power from photovoltaic (PV) panels. In all of MPPT methods, two parameters, i.e. perturbation period (Tp) and amplitude (ΔD) have a great effect on speed and accuracy of MPPT. Optimum value of the perturbation period is equal to the system settling time which is the system model-dependent parameter. Since the system model varies according to the change of irradiance level and temperature, the value of Tp has to be determined online. In this paper, the parametric identification method is adopted to identify the online value of Tp. The proposed method is based on the dichotomous coordinate descent-recursive least squares (DCD-RLS) algorithm and uses an infinite impulse response (IIR) adaptive filter as the system model. Computation of this algorithm is based on an efficient, fixed-point, and iterative approach with no explicit division operations; these features are highly suitable for online applications. As a result, the proposed method compared to previous works leads to more accurate and faster identification of the system settling time. In order to test and validate the proposed method, it has been simulated and implemented to be further validated with experimental data.
关键词： Photovoltaic Systems,Perturbation Period,Recursive Least Squares (RLS),Dichotomous Coordinate Descent (DCD),Maximum Power Point Tracking (MPPT),System Identification
更新于2025-09-23 15:21:21