arXiv subjects

Xingyu Zhang

Publications and source records attributed to Xingyu Zhang.

At least 73 records · Page 4Linked to original sources

arXiv2024

Precision Rehabilitation for Patients Post-Stroke based on Electronic Health Records and Machine Learning

In this study, we utilized statistical analysis and machine learning methods to examine whether rehabilitation exercises can improve patients post-stroke functional abilities, as well as forecast the improvement in functional abilities. Our dataset is patients' rehabilitation exercises and demographic information recorded in the unstructured electronic health records (EHRs) data and free-text rehabilitation procedure notes. We collected data for 265 stroke patients from the University of Pittsburgh Medical Center. We employed a pre-existing natural language processing (NLP) algorithm to extract data on rehabilitation exercises and developed a rule-based NLP algorithm to extract Activity Measure for Post-Acute Care (AM-PAC) scores, covering basic mobility (BM) and applied cognitive (AC) domains, from procedure notes. Changes in AM-PAC scores were classified based on the minimal clinically important difference (MCID), and significance was assessed using Friedman and Wilcoxon tests. To identify impactful exercises, we used Chi-square tests, Fisher's exact tests, and logistic regression for odds ratios. Additionally, we developed five machine learning models-logistic regression (LR), Adaboost (ADB), support vector machine (SVM), gradient boosting (GB), and random forest (RF)-to predict outcomes in functional ability. Statistical analyses revealed significant associations between functional improvements and specific exercises. The RF model achieved the best performance in predicting functional outcomes. In this study, we identified three rehabilitation exercises that significantly contributed to patient post-stroke functional ability improvement in the first two months. Additionally, the successful application of a machine learning model to predict patient-specific functional outcomes underscores the potential for precision rehabilitation.

cs.LG↗

arXiv2024

Landmark-Guided Cross-Speaker Lip Reading with Mutual Information Regularization

Lip reading, the process of interpreting silent speech from visual lip movements, has gained rising attention for its wide range of realistic applications. Deep learning approaches greatly improve current lip reading systems. However, lip reading in cross-speaker scenarios where the speaker identity changes, poses a challenging problem due to inter-speaker variability. A well-trained lip reading system may perform poorly when handling a brand new speaker. To learn a speaker-robust lip reading model, a key insight is to reduce visual variations across speakers, avoiding the model overfitting to specific speakers. In this work, in view of both input visual clues and latent representations based on a hybrid CTC/attention architecture, we propose to exploit the lip landmark-guided fine-grained visual clues instead of frequently-used mouth-cropped images as input features, diminishing speaker-specific appearance characteristics. Furthermore, a max-min mutual information regularization approach is proposed to capture speaker-insensitive latent representations. Experimental evaluations on public lip reading datasets demonstrate the effectiveness of the proposed approach under the intra-speaker and inter-speaker conditions.

cs.AI↗

arXiv2023

Improving photon number resolvability of a superconducting nanowire detector array using a level comparator circuit

Photon number resolving (PNR) capability is very important in many optical applications, including quantum information processing, fluorescence detection, and few-photon-level ranging and imaging. Superconducting nanowire single-photon detectors (SNSPDs) with a multipixel interleaved architecture give the array an excellent spatial PNR capability. However, the signal-to-noise ratio (SNR) of the photon number resolution (SNRPNR) of the array will be degraded with increasing the element number due to the electronic noise in the readout circuit, which limits the PNR resolution as well as the maximum PNR number. In this study, a 16-element interleaved SNSPD array was fabricated, and the PNR capability of the array was investigated and analyzed. By introducing a level comparator circuit (LCC), the SNRPNR of the detector array was improved over a factor of four. In addition, we performed a statistical analysis of the photon number on this SNSPD array with LCC, showing that the LCC method effectively enhances the PNR resolution. Besides, the system timing jitter of the detector was reduced from 90 ps to 72 ps due to the improved electrical SNR.

physics.app-ph↗

arXiv2023

NP-RDMA: Using Commodity RDMA without Pinning Memory

Remote Direct Memory Access (RDMA) has been haunted by the need of pinning down memory regions. Pinning limits the memory utilization because it impedes on-demand paging and swapping. It also increases the initialization latency of large memory applications from seconds to minutes. To remove memory pining, existing approaches often require special hardware which supports page fault, and still have inferior performance. We propose NP-RDMA, which removes memory pinning during memory registration and enables dynamic page fault handling with commodity RDMA NICs. NP-RDMA does not require NICs to support page fault. Instead, by monitoring local memory paging and swapping with MMU-notifier, combining with IOMMU/SMMU-based address mapping, NP-RDMA efficiently detects and handles page fault in the software with near-zero additional latency to non-page-fault RDMA verbs. We implement an LD_PRELOAD library (with a modified kernel module), which is fully compatible with existing RDMA applications. Experiments show that NP-RDMA adds only 0.1{\sim}2 μs latency under non-page-fault scenarios. Moreover, NP-RDMA adds only 3.5{\sim}5.7 μs and 60 μs under minor or major page faults, respectively, which is 500x faster than ODP which uses advanced NICs that support page fault. With non-pinned memory, Spark initialization is 20x faster and the physical memory usage reduces by 86% with only 5.4% slowdown. Enterprise storage can expand to 5x capacity with SSDs while the average latency is only 10% higher. To the best of our knowledge, NP-RDMA is the first efficient and application-transparent software approach to remove memory pinning using commodity RDMA NICs.

cs.NI↗

arXiv2023

Lee-Yang zeros and quantum Fisher information matrix in a nonlinear system

The distribution of Lee-Yang zeros not only matters in thermodynamics and quantum mechanics, but also in mathematics. Hereby we propose a nonlinear quantum toy model and discuss the distribution of corresponding Lee-Yang zeros. Utilizing the coupling between a probe qubit and the nonlinear system, all Lee-Yang zeros can be detected in the dynamics of the probe qubit by tuning the coupling strength and linear coefficient of the nonlinear system. Moreover, the analytical expression of the quantum Fisher information matrix at the Lee-Yang zeros is provided, and an interesting phenomenon is discovered. Both the coupling strength and temperature can simultaneously attain their precision limits at the Lee-Yang zeros. However, the probe qubit cannot work as a thermometer at a Lee-Yang zero if it sits on the unit circle.

quant-ph↗

arXiv2023

Quantum dynamic response-based NV-diamond magnetometry: Robustness to decoherence and applications in motion detection of magnetic nanoparticles

We propose a novel quantum sensing protocol that leverages the dynamical response of physical observables to quenches in quantum systems. Specifically, we use the nitrogen-vacancy (NV) color center in diamond to realize both scalar and vector magnetometry via quantum response. Furthermore, we suggest a method for detecting the motion of magnetic nanoparticles, which is challenging with conventional interference-based sensors. To achieve this, we derive the closed exact form of the Berry curvature corresponding to NV centers and design quenching protocols to extract the Berry curvature via dynamical response. By constructing and solving non-linear equations, the magnetic field and instantaneous motion velocity of the magnetic nanoparticle can be deduced. We investigate the feasibility of our sensing scheme in the presence of decoherence and show through numerical simulations that it is robust to decoherence. Intriguingly, we have observed that a vanishing nuclear spin polarization in diamond actually benefits our dynamic sensing scheme, which stands in contrast to conventional Ramsey-based schemes. In comparison to Ramsey-based sensing schemes, our proposed scheme can sense an arbitrary time-dependent magnetic field, as long as its time dependence is nearly adiabatic.

quant-ph↗

arXiv2023

Superconducting nanowire diode

Semiconducting diode with nonreciprocal transport effect underlies the cornerstone of contemporary integrated circuits (ICs) technology. Due to isotropic superconducting properties and the lack of breaking of inversion symmetry for conventional s-wave superconductors, such a superconducting peer is absent. Recently, a series of superconducting structures, including superconducting superlattice and quantum-material-based superconducting Josephson junction, have exhibited a superconducting diode effect in terms of polarity-dependent critical current. However, due to complex structures, these composite systems are not able to construct large-scale integrated superconducting circuits. Here, we demonstrated the minimal superconducting electric component-superconducting nanowire-based diode with a nonreciprocal transport effect under a perpendicular magnetic field, in which the superconducting to normal metallic phase transition relies on the polarity and amplitude of the bias current. Our nanowire diodes can be reliably operated nearly at all temperatures below the critical temperature, and the rectification efficiency at 2 K can be more than 24%. Moreover, the superconducting nanowire diode is able to rectify both square wave and sine wave signals without any distortion. Combining the superconducting nanowire-based diodes and transistors, superconducting nanowires hold the possibility to construct novel low-dissipation superconducting ICs.

cond-mat.supr-con↗

arXiv2023

A fully packaged multi-channel cryogenic module for optical quantum memories

Realizing a quantum network will require long-lived quantum memories with optical interfaces incorporated into a scalable architecture. Color centers quantum emitters in diamond have emerged as a promising memory modality due to their optical properties and compatibility with scalable integration. However, developing a scalable color center emitter module requires significant advances in the areas of heterogeneous integration and cryogenically compatible packaging. Here we report on a cryogenically stable and network compatible quantum-emitter module for memory use. This quantum-emitter module is a significant development towards advanced quantum networking applications such as distributed sensing and processing.

quant-ph↗

arXiv2022

Single photon detection performance of highly disordered NbTiN thin films

We experimentally investigated the detection performance of highly disordered NbxTi1-xN based superconducting nanowire single photon detectors (SNSPDs). The dependence on the composition of the transition temperature Tc for NbxTi1-xN films show a dome-like behavior on the Nb content, with a maximal Tc at xNb~0.65 , and the Nb0.65Ti0.35N films also combine relatively large sheet resistance and intermediate residual resistivity ratio. Moreover, 60-nm-wide and 7-nm-thick Nb0.65Ti0.35N nanowires show a switching current as high as 14.5 uA, and saturated intrinsic detection efficiency with a plateau of more than 2 uA at 2.4 K. Finally, the corresponding SNSPDs on an alternative SiO2/Ta2O5 dielectric mirror showed a system detection efficiency of approximately 92% for 1550 nm photons, and the timing jitter is around 26 ps. Our results demonstrate that the highly disordered NbxTi1-xN films are promising for fabricating SNSPDs for near- and middle-infrared single photons with high detection efficiency and low timing jitter.

cond-mat.supr-con↗

arXiv2022

Direct measurement of quantum Fisher information

In the adiabatic perturbation theory, Berry curvature is related to the generalized force, and the quantum metric tensor is linked with energy fluctuation. While the former is tested with numerous numerical results and experimental realizations, the latter is less considered. Quantum Fisher information, key to quantum precision measurement, is four times quantum metric tensor. It is difficult to relate the quantum Fisher information with some physical observable. One interesting candidate is square of the symmetric logarithmic derivative, which is usually tough to obtain both theoretically and experimentally. The adiabatic perturbation theory enlightens us to measure the energy fluctuation to directly extract the quantum Fisher information. In this article, we first adopt an alternative way to derive the link of energy fluctuation to the quantum Fisher information. Then we numerically testify the direct extraction of the quantum Fisher information based on adiabatic perturbation in two-level systems and simulate the experimental realization in nitrogen-vacancy center with experimentally practical parameters. Statistical models such as transverse field Ising model and Heisenberg spin chains are also discussed to compare with the analytical result and show the level crossing respectively. Our discussion will provide a new practical scheme to measure the quantum Fisher information, and will also benefit the quantum precision measurement and the understand of the quantum Fisher information.

quant-ph↗

arXiv2022

Instantaneous indirect measurement principle in quantum mechanics

In quantum systems, the measurement of operators and the measurement of the quantum states of the system are very challenging tasks. In this Letter, we propose a method to obtain the average value of one operator in a certain state by measuring the instantaneous change of the average value of another operator with the assistance of a known reference state. We refer to this measurement method as the instantaneous indirect measurement method. By studying the application of this method to some typical models, we find that this measurement can be applied to the measurement of an arbitrary state of a quantum system. Furthermore, for the system to be measured, we find that such measurement neither significantly affects the wave function of the system nor causes wave function collapse of the system. Also, our study shows that when two independent systems are coupled, the information mapping between them is done instantaneously. Finally, we discuss applying this measurement method to the measurement of quantum Fisher information, which quantizes the limited accuracy of estimating a parameter from a quantum state.

quant-ph↗

arXiv2022

Probing Script Knowledge from Pre-Trained Models

Script knowledge is critical for humans to understand the broad daily tasks and routine activities in the world. Recently researchers have explored the large-scale pre-trained language models (PLMs) to perform various script related tasks, such as story generation, temporal ordering of event, future event prediction and so on. However, it's still not well studied in terms of how well the PLMs capture the script knowledge. To answer this question, we design three probing tasks: inclusive sub-event selection, starting sub-event selection and temporal ordering to investigate the capabilities of PLMs with and without fine-tuning. The three probing tasks can be further used to automatically induce a script for each main event given all the possible sub-events. Taking BERT as a case study, by analyzing its performance on script induction as well as each individual probing task, we conclude that the stereotypical temporal knowledge among the sub-events is well captured in BERT, however the inclusive or starting sub-event knowledge is barely encoded.

cs.CL↗

arXiv2021

Extreme expected values and their applications in quantum information processing

We consider the probability distribution when the monotonic function $F(X)$ of the independent variable $X$ takes the maximum or minimum expected value under the two constraints of a certain probability and a certain expected value of the independent variable $X$. We proposed an equal probability and equal expected value splitting method. With this method, we proved four inequalities, and two of them can be reduced to Jensen's inequalities. Subsequently, we find that after dividing the non-monotone function $H(X)$ into multiple monotone intervals, the problem of solving the maximum and minimum expected values of $H(X)$ can be transformed into the problem of solving the extreme value of a multiple-variable function. Finally, we apply the proved theory to solve three problems in quantum information processing. When studying the quantum parameter estimation in Mach-Zehnder interferometer, for an equal total input photon number, we find an optimal path-symmetric input state that makes the quantum Fisher information take the maximum value, and we prove that the NOON state is the path-symmetric state that makes the quantum Fisher information takes the minimum value. When studying the quantum parameter estimation in Landau-Zener-Jaynes-Cummings model, we find the optimal initial state of the cavity field that makes the system obtain the maximum quantum Fisher information. Finally, for an equal initial average photon number, we find the optimal initial state of the cavity field that makes the Tavis-Cummings quantum battery have the maximum stored energy and the maximum average charging power.

quant-ph↗

arXiv2021

Probing Ultralight Bosons with Compact Eccentric Binaries

Ultralight bosons can be abundantly produced through superradiance process by a spinning black hole and form a bound state with hydrogen-like spectrum. We show that such a "gravitational atom" typically possesses anomalously large mass quadrupole and leads to significant orbital precession when it forms an eccentric binary with a second compact object. Dynamically formed black hole binaries or pulsar-black hole binaries are typically eccentric during their early inspirals. We show that the large orbital precession can generate distinct and observable signature in their gravitational wave or pulsar timing signals.

gr-qc↗

arXiv2020

Influence of kinetic energy on the metrology of Rabi frequency

The interacting model describing the Rabi transition is essential in studying atom-photon interactions, where the kinetic energy term is often neglected for the convenience of analysis. We first study the approximation through the fidelity approach and verify its valid region in the parameter space of detuning and momentum. We find that as the radiation field's momentum and the absolute value of detuning decrease, the approximation becomes valid. We further discover that the omission of the kinetic energy term will overestimate the measuring accuracy of the Rabi frequency in some parameter regions and underestimate the precision in other regimes with Fisher information tools' help. Notably, a specific choice of the initial Gaussian state's variance in position space will improve the measuring accuracy when we take the kinetic energy term into account. We also study the realistic measurement of the Rabi frequency for cases with and without the kinetic energy.

quant-ph↗

arXiv2020

Enhanced cavity coupling to silicon monovacancies in 4-H Silicon Carbide using below bandgap laser irradiation and low temperature thermal annealing

The negatively charged silicon monovacancy $V_{Si}^-$ in 4H-silicon carbide (SiC) is a spin-active point defect that has the potential to act as a qubit or quantum memory in solid-state quantum computation applications. Photonic crystal cavities (PCCs) can augment the optical emission of the $V_{Si}^-$, yet fine-tuning the defect-cavity interaction remains challenging. We report on two post-fabrication processes that result in enhancement of the $V_1^{'}$ optical emission from our 1-dimensional PCCs, indicating improved coupling between the ensemble of silicon vacancies and the PCC. One process involves below bandgap illumination at 785 nm and 532 nm wavelengths and above bandgap illumination at 325 nm, carried out at times ranging from a few minutes to several hours. The other process is thermal annealing at $100^o C$, carried out over 20 minutes. Every process except above bandgap irradiation improves the defect-cavity coupling, manifested in augmented Purcell factor enhancement of the $V_1^{'}$ zero phonon line at 77K. The below bandgap laser process is attributed to a modification of charge states, changing the relative ratio of $V_{Si}^0$ (dark state) to $V_{Si}^-$ (bright state), while the thermal annealing process may be explained by diffusion of carbon interstitials, $C_i$, that subsequently recombine with other defects to create additional $V_{Si}^-$s. Above bandgap radiation is proposed to initially convert $V_{Si}^{0}$ to $V_{Si}^-$, but also may lead to diffusion of $V_{Si}^-$ away from the probe area, resulting in an irreversible reduction of the optical signal. Observations of the PCC spectra allow insights into defect modifications and interactions within a controlled, designated volume and indicate pathways to improve defect-cavity interactions.

physics.optics↗

arXiv2020

On optimal ordering in the optimal stopping problem

In the classical optimal stopping problem, a player is given a sequence of random variables $X_1\ldots X_n$ with known distributions. After observing the realization of $X_i$, the player can either accept the observed reward from $X_i$ and stop, or reject the observed reward from $X_i$ and continue to observe the next variable $X_{i+1}$ in the sequence. Under any fixed ordering of the random variables, an optimal stopping policy, one that maximizes the player's expected reward, is given by the solution of a simple dynamic program. In this paper, we investigate the relatively less studied question of selecting the order in which the random variables should be observed so as to maximize the expected reward at the stopping time. To demonstrate the benefits of order selection, we prove a novel prophet inequality showing that, when the support of each random variable has size at most 2, the optimal ordering can achieve an expected reward that is within a factor of 1.25 of the expected hindsight maximum; this is an improvement over the corresponding factor of 2 for the worst-case ordering. We also provide a simple $O(n^2)$ algorithm for finding an optimal ordering in this case. Perhaps surprisingly, we demonstrate that a slightly more general case - each random variable $X_i$ is restricted to have 3-point support of form $\{0, m_i, 1\}$ - is NP-hard, and provide an FPTAS for that case.

cs.DM↗

arXiv2019

Charging of quantum batteries with general harmonic power

We analyse the charging process of quantum batteries with general harmonic power. To describe the charge efficiency, we introduce the charge saturation and the charging power, and divide the charging mode into the saturated charging mode and the unsaturated charging mode. The relationships between the time-dependent charge saturation and the parameters of general driving field are discussed both analytically and numerically. And according to the Floquet theorem, we give the expressions of time-dependent charge saturation with the quasiengery and the Floquet states of the system. With both the analytical and numerical results, we find the optimal parameters to reach the best charging efficiency.

quant-ph↗