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One of the main quests in quantum metrology is to attain the ultimate precision limit with given resources, where the resources are not only of the number of queries, but more importantly of the allowed strategies. With the same number of queries, the restrictions on the strategies constrain the achievable precision. In this work, we establish a systematic framework to identify the ultimate precision limit of different families of strategies, including the parallel, the sequential, and the indefinite-causal-order strategies, and provide an efficient algorithm that determines an optimal strategy within the family of strategies under consideration. With our framework, we show there exists a strict hierarchy of the precision limits for different families of strategies., Comment: 6 + 23 pages, 10 figures; close to the published version

Nowadays, high-quality metal oxide thin film transistors grown by solution process have the most potential to replace the traditional a-Si TFT as the next generation of transparent electronics for various applications. However, the low intrinsic carrier concentration and poor charge carrier mobility of metal oxide thin film hinder its development. In order to solve these problems, the heterojunction structure was proposed. In this study, the Indium Oxide/Indium Gallium Oxide (In2O3/IGO) heterojunction was systematically investigated, and the existence of a two-dimensional electron gas was found. There is a large accumulation of carriers at the In2O3/IGO heterojunction interface, and the Hall tests show that the In2O3/IGO heterojunction has the highest carrier concentration of 7.82 × 1012 cm−2 and a carrier mobility of 10.22 cm2V−1s−1. This research can provide a theoretical guidance for promoting the development of oxide thin film transistor technology.

This paper clarifies the relationship between dynamic fairness, inequality, and mobility. Suppose agents assess the degree of fairness in a society based on the distribution of expected future income, conditional on current income. Within Markovian environments characterised by stochastically monotone transition rules, in which a globally stable steady-state income distribution exists, we show that the degree of dynamic fairness is jointly determined by inequality and mobility. When mobility is held constant, inequality harms fairness; on the contrary, when inequality is held constant, mobility enhances fairness. Moreover, any particular degree of fairness can be obtained by one of many combinations of inequality and mobility, and trade-offs always exists between any two such pairs. Our results hold true with both the standard Lorenz curve and the generalised Lorenz curve and extend to multi-period settings.

The accelerated aging of China’s population will inevitably increase the burden of social retirement and significantly impact the development of financial markets, which is not conducive to sustainable social development. A proper allocation of financial assets will enable households to earn more property income and facilitate the appropriate allocation of social capital. The aging of the population is an essential factor affecting the allocation of financial assets to households. This paper examines the impact of an aging population on household financial asset allocation based on data from the 2015, 2017, and 2019 China Household Finance Surveys (CHFS). The study finds that aging significantly negatively affects household risky financial asset participation, depth of participation, and diversity. The findings remain robust after robustness tests using a two-way fixed effects model. In addition, this paper examines the mechanisms of influence from the perspectives of both risk aversion and financial literacy. In terms of mediating variables, aging increases the risk aversion of household heads, and an increase in risk aversion discourages households from investing in risky financial assets. In terms of moderating variables, the dampening effect of aging on investment in risky financial assets diminishes as financial literacy increases. In addition, empirical findings based on heterogeneity find that aging has a stronger negative impact on risky financial asset participation, depth of participation, and diversity in rural areas. Aging has a stronger negative impact on risky financial asset participation for households with children.

Most previous efforts on quantum error correction focused on either extending classical error-correction schemes to the quantum regime by performing a perfect correction on a subset of errors or seeking a recovery operation to maximize the fidelity between an input state and its corresponding output state of a noisy channel. There are few results concerning quantum error precompensation. Here we design an error-precompensated input state for an arbitrary quantum noisy channel and a given target output state. By following a procedure, the required input state, if it exists, can be analytically obtained in single-partite systems. Furthermore, we also present semidefinite programs to numerically obtain the error-precompensated input states with maximal fidelities between the target state and the output state. The numerical results coincide with the analytical results.

The unsteady flow in the front side window region of the vehicle can generate hydrodynamic and acoustic pressure on the front side window, which can influence the interior sound field. The hydrodynamic pressure on the front side window was achieved by the incompressible wall-modeled large-scale eddy simulation (WMLES) or improved delayed detached eddy simulation (IDDES), and the hybrid computational aeroacoustics (CAA) method based on acoustic perturbation equations (APE) was employed to achieve the acoustic pressure on the front side window. The numerical results of both hydrodynamic and acoustic pressure ware validated by the wind tunnel experiment, especially the corrected force analysis technique (CFAT) is employed to validate the acoustic pressure. The comparison of hydrodynamic and acoustic pressure on the front side window was performed by the Dynamic Mode Decomposition (DMD). Results show that the hydrodynamic pressure regionally distributes on the front side window and most energy concentrates on area interacted with the side mirror wake, while the acoustic pressure distributes uniformly on the front side window acting as a diffusion field and the energy disperses in frequency region.

In most quantum technologies, measurements need to be performed on the parametrized quantum states to transform the quantum information to classical information. The measurements, however, inevitably distort the information. The characterization of the discrepancy is an important subject in quantum information science, which plays a key role in understanding the difference between the structures of the quantum and classical information. Here we analyze the discrepancy in terms of the Fisher information metric and present a framework that can provide analytical bounds on the difference under hierarchical quantum measurements. Specifically, we present a set of analytical bounds on the difference between the quantum and classical Fisher information metric under hierarchical p-local quantum measurements, which are measurements that can be performed collectively on at most p copies of quantum states. The results can be directly transformed to the precision limit in multi-parameter quantum metrology, which leads to characterizations of the tradeoff among the precision of different parameters. The framework also provides a coherent picture for various existing results by including them as special cases., This is a short version of arXiv:2109.05807

Using density functional theory combined with

Although perovskite/two-dimensional (2D) materials heterojunctions have been employed to improve the optoelectronic performance of perovskite photodetectors and solar cells, effects of the intrinsic potential difference (

Heisenberg scaling characterizes the ultimate precision of parameter estimation enabled by quantum mechanics, which represents an important quantum advantage of both theoretical and technological interest. Here, we present a comprehensive and rigorous study of the attainability of strong, global notions of Heisenberg scaling (in contrast to the commonly studied local estimation based on e.g. quantum Fisher information) in the fundamental problem of quantum metrology, in noisy environments. As our first contribution, we formally define two useful notions of Heisenberg scaling in global estimation respectively based on the average estimation error and the limiting distribution of estimation error (which we highlight as a practically important figure of merit). A main result of this work is that for the standard phase damping noise, an O(n −1) noise rate is a necessary and sufficient condition for attaining global Heisenberg scaling. We first prove that O(n −1) is an upper bound on the noise rate for Heisenberg scaling to be possible, and then show by constructing a ‘robust’ estimation procedure that global Heisenberg scaling in both senses can indeed be achieved under Θ(n −1) noise. In addition, we provide a practically more friendly adaptive protocol using only an one-qubit memory, which achieves global Heisenberg scaling in terms of limiting distribution as well under O(n −1) noise.

β-Ga2O3/graphene heterostructure engineering has been regarded as an effective method to improve the optoelectronic performance of the β-Ga2O3 device. Here, hydrogenation/fluorination covalent functionalized graphene (HC/FC) was employed, and the synergistic effect of covalent functionalization and intrinsic electric field ( Ein) was introduced to further improve and understand the interfacial properties of the heterostructure. Under the covalent functionalization, type-II band alignment with UV-infrared dual-band absorption was found for β-Ga2O3/HC heterostructure, while reserved type-II band alignment with hole doping was realized for p-type β-Ga2O3/FC heterostructure. Upon introducing the synergistic effect of covalent functionalization and Ein for β-Ga2O3/hydro-fluorinated graphene (HCF) heterostructure, except for the above similar characters, both the band offsets and optical absorption are further enhanced in β-Ga2O3/HCF heterostructures. When the direction of intrinsic Ein points to the contact interface, the Fermi level of β-Ga2O3/F-HCF was much closer to the valence band of β-Ga2O3. It was thought that the synergistic effect of covalent functionalization and Ein was more beneficial to promote the application of p-type β-Ga2O3. These findings were deeply revealed by the band levels, electrostatic potential, and charge transfer introduced. Our results were expected to provide useful insight into the synergistic effect of covalent functionalization and intrinsic Ein as well as to enhance the application potential of β-Ga2O3/graphene-based optoelectronic devices.

Generally, growing phase pure CsPbBr3 single crystals is challenging, and CsPb2Br5 or Cs4PbBr6 by‐products are usually formed due to the different solubilities of CsBr and PbBr2 in the single solvent. Herein, the growth of high‐quality phase pure CsPbBr3 perovskite single crystals at room temperature by a humidity controlled solvent evaporation method is reported first. Meanwhile, the room temperature phase transition process from three dimensional (3D) cubic CsPbBr3 to two dimensional (2D) layered tetragonal CsPb2Br5 and the detailed mechanism induced by humidity are revealed. Moreover, compared with the organic–inorganic perovskite, the prepared CsPbBr3 single crystals are much more stable under high humidity, which satisfies the long‐term working conditions of X‐ray detectors. The X‐ray detectors based on CsPbBr3 single crystals show a high sensitivity and a low detection limit of 1.89 μGyair s–1, all of which meet the needs of medical diagnosis., The mixed products of CsBr and PbBr2 are rich and diverse, which is a phenomenon of people scratching their heads. In the humidity controlled low‐temperature preparation process, the mechanism of its diversity is uncovered through the transformations of products under the influence of different conditions and a valuable guidance is provided for the subsequent crystal acquisition and growth.

The polarization switching behaviors of ultrathin films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) capacitors with different thicknesses of top PEDOT-PSSH layer have been studied. The polarization switching results are related to an effective internal electric field, and a large, permanent, internal electric field can be ensured by introducing a symmetric PEDOT-PSSH layer into the capacitors. The switching speed is potentially influenced by the PEDOT-PSSH layer and the asymmetric PEDOT-PSSH layer leads to a different density of surface charge, resulting in a build-in field. As a result, these enhanced switching dynamics in spin-coating 25 nm P(VDF-TrFE) copolymer films are achieved by introduced a symmetric electroactive layer to optimize morphology and the internal electric field. At high temperature (60 °C), we also show that the enhanced switching speed is two times as fast as what is measured at room temperature (25 °C) because the temperature depended active field is related to the switching kinetic energy. Switching time of P(VDF-TrFE) films with an electroactive layer as a function of the number of switching cycles show the excellent switching characteristics of ferroelectric capacitors.

Magnetic sensing based on nitrogen-vacancy (NV) center ensembles provides unique signal-to-noise ratio and sensitivity for physical and biological measurements at room temperature. However, inhomogeneous microwave (MW) coupling with NV ensembles and different field projections onto the NV axes lead to nonsynchronous spin dephasing and pose severe challenges to magnetic sensing. In this paper, we experimentally investigated the impact of the MW field uniformity on the DC magnetic sensing based on NV ensembles. We obtained different MW field uniformity between 42% and 93% in the same direction using a square split ring resonator. The uniformity and direction of the MW field was mapped using a wide-field magnetic imaging system. The magnetic sensing with the MW frequency modulation technology confirmed the consistence between the theoretical analysis and experimental results. The sensitivity was enhanced by nearly seven times with the best MW field uniformity. Our study can promote the further application and development of magnetic sensing devices based on solid-state spin ensembles.

The pressure excitation on automotive front side window acts as an indicator of the unsteady flow and wind noise in the front side window region. The complex unsteady flow in this area generates a wider range of vortex structures resulting in the nonhomogeneous and complex pressure excitation on side glass. The description of the pressure field, which can consider the nonhomogeneous in the exact space, is needed to better solve the vibration and noise problems. The turbulent pressure excitation on side window was achieved by the incompressible improved delayed detached-eddy simulation, which is validated by the wind tunnel experiment. The reduced-order modeling methods, including the proper orthogonal decomposition and the dynamic mode decomposition, were employed to describe the pressure excitation on side glass. The dynamic mode decomposition modes separate the pressure excitation into three parts just corresponding to three main flow structures in the front side window region: the vortex shedding of the side mirror (lower frequency range), pedestal vortex (middle frequency range), and A-pillar vortex (higher frequency range). The turbulent pressure excitation generated by the vortex shedding of the side mirror contributes most of the vibration of the side glass and then the wind noise in the cabin in the low-frequency range. (The characteristic frequency is around 60 Hz, which is close to both the measured coincidence frequency and the theoretical derivation value.) The dynamic mode decomposition analysis with the unique and exact frequency for each mode, considering the nonhomogeneous of the pressure excitation, has potential to understand and solve the vibration and wind noise problems.

The wake of a circular cylinder coated with porous media was experimentally investigated by hot-wire anemometry, particle image velocimetry (PIV) and smoke-wire visualization. Mean velocity and Reynolds stresses in the streamwise and lateral are eliminated obviously for porous layer coating, especially in the centerline. The vortex formation length is elongated, and the width of the wake region is expanded by coating porous media. The Strouhal number of vortex shedding is 0.162 for the porous cylinder, which is smaller than 0.182 for the bare one due to the widened wake. Additionally, porous layer significantly regulates the flow field, which can be detected distinctly by smoke-wire visualization and transient PIV data. The proper orthogonal decomposition (POD) was further used to analyze PIV data with a view to extract dominant coherent structures in the wake. Moreover, a phase-averaged low-order model was applied to provide a comprehensive description of the dynamics of the first four modes. The first two POD modes, showing the signature of asymmetrical vortex shedding and predominating in the wake of the bare cylinder, are weakened dramatically for porous layer coating and present abrupt degradation in the midline. Meanwhile, mode 3 and mode 4, representing the symmetrical vortex shedding, occupy higher energy for porous cylinder. The study reveals that the porous layer coating delays the roll-up of shear layer and weakens the interaction between them, and thus, the vortex region is shifted further downstream.

The Heisenberg scaling, which scales as N^{-1} in terms of the number of particles or T^{-1} in terms of the evolution time, serves as a fundamental limit in quantum metrology. Better scalings, dubbed as "super-Heisenberg scaling," however, can also arise when the generator of the parameter involves many-body interactions or when it is time dependent. All these different scalings can actually be seen as manifestations of the Heisenberg uncertainty relations. While there is only one best scaling in the single-parameter quantum metrology, different scalings can coexist for the estimation of multiple parameters, which can be characterized by multiple Heisenberg uncertainty relations. We demonstrate the coexistence of two different scalings via the simultaneous estimation of the magnitude and frequency of a field where the best precisions, characterized by two Heisenberg uncertainty relations, scale as T^{-1} and T^{-2}, respectively (in terms of the standard deviation). We show that the simultaneous saturation of two Heisenberg uncertainty relations can be achieved by the optimal protocol, which prepares the optimal probe state, implements the optimal control, and performs the optimal measurement. The optimal protocol is experimentally implemented on an optical platform that demonstrates the saturation of the two Heisenberg uncertainty relations simultaneously, with up to five controls. As the first demonstration of simultaneously achieving two different Heisenberg scalings, our study deepens the understanding on the connection between the precision limit and the uncertainty relations, which has wide implications in practical applications of multiparameter quantum estimation.

Quantum control can be employed in quantum metrology to improve the precision limit for the estimation of unknown parameters. The optimal control, however, typically depends on the actual values of the parameters and thus needs to be designed adaptively with the updated estimations of those parameters. Traditional methods, such as gradient ascent pulse engineering (GRAPE), need to be rerun for each new set of parameters encountered, making the optimization costly, especially when many parameters are involved. Here we study the generalizability of optimal control, namely, optimal controls that can be systematically updated across a range of parameters with minimal cost. In cases where control channels can completely reverse the shift in the Hamiltonian due to a change in parameters, we provide an analytical method which efficiently generates optimal controls for any parameter starting from an initial optimal control found by either GRAPE or reinforcement learning. When the control channels are restricted, the analytical scheme is invalid, but reinforcement learning still retains a level of generalizability, albeit in a narrower range. In cases where the shift in the Hamiltonian is impossible to decompose to available control channels, no generalizability is found for either the reinforcement learning or the analytical scheme. We argue that the generalization of reinforcement learning is through a mechanism similar to the analytical scheme. Our results provide insights into when and how the optimal control in multiparameter quantum metrology can be generalized, thereby facilitating efficient implementation of optimal quantum estimation of multiple parameters, particularly for an ensemble of systems with ranges of parameters., 13 pages, 12 figures

In this paper, we consider the system where a superconducting qubit is coupled to a resonator acting as a harmonic oscillator. Unlike the existing work regarding estimation of the coupling strength or oscillator frequency, we aim to sense the amplitude of a microwave drive by utilizing the qubit as a quantum probe. Furthermore, in order to improve the estimation precision, we employ a periodic control protocol that is easy to be implemented in practice. Such improvement does not require any manipulation of the oscillator. The proposed strategy sheds light on a systematic study on estimation of the driving field in superconducting circuits by means of adding control.

Quantum discrimination and estimation are pivotal for many quantum technologies, and their performance depends on the optimal choice of probe state and measurement. Here we show that their performance can be further improved by suitably tailoring the pulses that make up the interferometer. Developing an optimal control framework and applying it to the discrimination and estimation of a magnetic field in the presence of noise, we find an increase in the overall achievable state distinguishability. Moreover, the maximum distinguishability can be stabilized for times that are more than an order of magnitude longer than the decoherence time., 9 pages, 5 figures

We study the effect of feedback controls in quantum parameter estimation. In particular, we study the estimation of a magnetic field with a spin in the presence of the spontaneous emission where feedback control, triggered by the detection of the emitted photons, is employed to improve the precision limit. We also study the effect of additional Hamiltonian controls and show that they can provide further improvement on the precision limit.

Experiments demonstrate very high precisions achieved simultaneously for multiple parameters with noncommuting generators., Quantum estimation of a single parameter has been studied extensively. Practical applications, however, typically involve multiple parameters, for which the ultimate precision is much less understood. Here, by relating the precision limit directly to the Heisenberg uncertainty relation, we show that to achieve the highest precisions for multiple parameters at the same time requires the saturation of multiple Heisenberg uncertainty relations simultaneously. Guided by this insight, we experimentally demonstrate an optimally controlled multipass scheme, which saturates three Heisenberg uncertainty relations simultaneously and achieves the highest precisions for the estimation of all three parameters in SU(2) operators. With eight controls, we achieve a 13.27-dB improvement in terms of the variance (6.63 dB for the SD) over the classical scheme with the same loss. As an experiment demonstrating the simultaneous achievement of the ultimate precisions for multiple parameters, our work marks an important step in multiparameter quantum metrology with wide implications.

The quantum speed limit is a fundamental concept in quantum mechanics, which aims at finding the minimum time scale or the maximum dynamical speed for some fixed targets. In a large number of studies in this field, the construction of valid bounds for the evolution time is always the core mission, yet the physics behind it and some fundamental questions like which states can really fulfill the target, are ignored. Understanding the physics behind the bounds is at least as important as constructing attainable bounds. Here we provide an operational approach for the definition of the quantum speed limit, which utilizes the set of states that can fulfill the target to define the speed limit. Its performances in various scenarios have been investigated. For time-independent Hamiltonians, it is inverse-proportional to the difference between the highest and lowest energies. The fact that its attainability does not require a zero ground-state energy suggests it can be used as an indicator of quantum phase transitions. For time-dependent Hamiltonians, it is shown that contrary to the results given by existing bounds, the true speed limit should be independent of the time. Moreover, in the case of spontaneous emission, we find a counterintuitive phenomenon that a lousy purity can benefit the reduction of the quantum speed limit., 9+9 pages, 10 figures