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Shuang Wang

Publications and source records attributed to Shuang Wang.

At least 127 records · Page 7Linked to original sources
arXiv2020

Gate-tunable van der Waals heterostructure for reconfigurable neural network vision sensor

Early processing of visual information takes place in the human retina. Mimicking neurobiological structures and functionalities of the retina provide a promising pathway to achieving vision sensor with highly efficient image processing. Here, we demonstrate a prototype vision sensor that operates via the gate-tunable positive and negative photoresponses of the van der Waals (vdW) vertical heterostructures. The sensor emulates not only the neurobiological functionalities of bipolar cells and photoreceptors but also the unique synaptic connectivity between bipolar cells and photoreceptors. By tuning gate voltage for each pixel, we achieve reconfigurable vision sensor for simultaneously image sensing and processing. Furthermore, our prototype vision sensor itself can be trained to classify the input images, via updating the gate voltages applied individually to each pixel in the sensor. Our work indicates that vdW vertical heterostructures offer a promising platform for the development of neural network vision sensor.

cond-mat.mtrl-sci↗
arXiv2019

Exploring the Latest Pantheon SNIa Dataset by Using Three Kinds of Statistics Techniques

In this work, we explore the cosmological consequences of the latest Type Ia supernova (SN Ia) data-set, Pantheon, by adopting the $wCDM$ model. The Pantheon data-set is the largest SN Ia samples till now, which contains 1048 supernovae on the redshift range $0 < z < 2.3$. Here we take into account three kinds of SN Ia statistics techniques, including: 1. magnitude statistics (MS), which is the traditional SN Ia statistics technique; 2. flux statistics (FS), which bases on the flux-averaging (FA) method; 3. improved flux statistics (IFS), which combines the advantages of MS and FS. It should be mentioned that, The IFS technique need to scan the $(z_{cut},Δz)$ parameters plane, where $z_{cut}$ and $Δz$ are redshift cut-off and redshift interval of FA, respectively. The results are shown as follows. (1) Using SN data-set only, the best FA recipe for IFS is $(z_{cut},Δz)=(0.1,0.08)$; (2) Comparing to the old SN data-set, JLA, adopting Pantheon data-set can reduce the $2σ$ error bars of equation of state $w$ by 38\%, 47\% and 53\% for MS, FS and IFS, respectively; (3) FS gives closer results to other observations, such as Baryon acoustic oscillations and Cosmic microwave background; (4) Compared with FS and IFS, MS more favors a Universe that will end in a "big rip".

astro-ph.CO↗
arXiv2019

Two-dimensional layered materials for memristive and neuromorphic applications

With many fantastic properties, memristive devices have been proposed as top candidate for next-generation memory and neuromorphic computing chips. Significant research progresses have been made in improving performance of individual memristive devices and in demonstrating functional applications based on small-scale memristive crossbar arrays. However, practical deployment of large-scale traditional metal oxides based memristive crossbar array has been challenging due to several issues, such as high-power consumption, poor device reliability, low integration density and so on. To solve these issues, new materials that possess superior properties are required. Two-dimensional (2D) layered materials exhibit many unique physical properties and show great promise in solving these challenges, further providing new opportunities to implement practical applications in neuromorphic computing. Here, recent research progress on 2D layered materials based memristive device applications is reviewed. We provide an overview of the progresses and challenges on how 2D layered materials are used to solve the issues of conventional memristive devices and to realize more complex functionalities in neuromorphic computing. Besides, we also provide an outlook on exploitation of unique properties of 2D layered materials and van der Waals heterostructures for developing new types of memristive devices and artificial neural mircrocircuits.

physics.app-ph↗
arXiv2019

Experimental investigation of the uncertainty relations with coherent light

Taking advantage of coherent light beams, we experimentally investigate the variancebased uncertainty relations and the optimal majorization uncertainty relation for the two-dimensional quantum mechanical system.Different from most of the experiments which devoted to record each individual quantum, we examine the uncertainty relations by measuring an ensemble of photons with two polarization degree of freedom characterized by the Stokes parameters which allow us to determine the polarization density matrix with high precision. The optimality of the recently proposed direct-sum majorization uncertainty relation is verified by measuring the Lorenz curves. Results show that the Lorenz curve method represents a faithful verification of the majorization uncertainty relation and the uncertainty relation is indeed an ensemble property of quantum system.

quant-ph↗
arXiv2019

Hacking the quantum key distribution system by exploiting the avalanche transition region of single photon detectors

Avalanche photodiode based single photon detectors, as crucial and practical components, are widely used in quantum key distribution (QKD) systems. For effective detection, most of these SPDs are operated in the gated mode, in which the gate is added to obtain high avalanche gain, and is removed to quench the avalanche. The avalanche transition region (ATR) is a certain existence in the process of adding and removing the gate. We first experimentally investigate the characteristic of the ATR, including in the commercial SPD and high-speed SPD, and then propose an ATR attack to control the detector. In the experiment of hacking the plug-and-play QKD system, Eve only introduces less than 0.5 % quantum bit error rate, and almost leaves no traces of her presence including the photocurrent and afterpulse probability. We finally give possible countermeasures against this attack.

quant-ph↗
arXiv2019

Robust countermeasure against detector control attack in practical quantum key distribution system

In real-life implementations of quantum key distribution (QKD), the physical systems with unwanted imperfections would be exploited by an eavesdropper. Based on imperfections in the detectors, detector control attacks have been successfully launched on several QKD systems, and attracted widespread concerns. Here, we propose a robust countermeasure against these attacks just by introducing a variable attenuator in front of the detector. This countermeasure is not only effective against the attacks with blinding light, but also robust against the attacks without blinding light which are more concealed and threatening. Different from previous technical improvements, the single photon detector in our countermeasure model is treated as a blackbox, and the eavesdropper can be detected by statistics of the detection and error rates of the QKD system. Besides theoretical proof, the countermeasure is also supported by an experimental demonstration. Our countermeasure is general in sense that it is independent of the technical details of the detector, and can be easily applied to the existing QKD systems.

quant-ph↗
arXiv2019

Improving the performance of Twin-Field Quantum Key Distribution

Among the various versions of the twin-field quantum key distribution (TF-QKD) protocol [M.Lucamarini, Z. Yuan, J. Dynes, and A. Shields, Nature (London) 557, 400 (2018)] that can overcome the rate-distance limit, the TF-QKD without phase postselection proposed by Cui et al. [Phys. Rev. Appl. 11, 034053 (2019)] is an elegant TF-QKD that can provide high key rates since the postselection of global phases has been removed. However, the achievable distance of this variant is shorter than that of the original phase-matching QKD [X. Ma, P. Zeng, and H. Zhou, Phys. Rev. X 8, 031043 (2018)]. In this paper, we propose a method for improving its performance by introducing an additional decoy mode. The upper bound of the information leakage can be more tightly estimated; hence, both the key rate and the achievable distance are significantly improved. Interestingly, the operation of the proposed additional decoy mode is the same as that of the code mode; hence, it does not introduce difficulties into the experimental system. In addition, the improvement is substantial with finite decoy states, which is meaningful in practice.

quant-ph↗
arXiv2019

Generating single longitudinal mode entangled photons in telecom band via a submillimeter monolithic cavity

A high-quality, compact, and narrow-bandwidth entangled photon source (EPS) is indispensable for realization of many quantum communication protocols. Usually, a free space cavity containing a nonlinear crystal is used to generate a narrow bandwidth EPS through spontaneous parametric down-conversion (SPDC). One major drawback is that this occupies a large space and requires complex optical and electrical control systems. Here we present a simple and compact method to generate a single-longitudinal-mode time-energy EPS via type II SPDC in a submillimeter Fabry-Perot cavity. We characterize the quality of the EPS by measuring the coincidence to accidental coincidence ratio, the two-photon time cross-correlation function and the two-photon interference fringes. All measured results clearly demonstrate that the developed source is of high quality when compared with EPSs generated using other configurations. We believe this source is very promising for applications in the quantum communication field.

quant-ph↗
arXiv2019

Toward Scalable Fully Homomorphic Encryption Through Light Trusted Computing Assistance

It has been a long standing problem to securely outsource computation tasks to an untrusted party with integrity and confidentiality guarantees. While fully homomorphic encryption (FHE) is a promising technique that allows computations performed on the encrypted data, it suffers from a significant slow down to the computation. In this paper we propose a hybrid solution that uses the latest hardware Trusted Execution Environments (TEEs) to assist FHE by moving the bootstrapping step, which is one of the major obstacles in designing practical FHE schemes, to a secured SGX enclave. TEEFHE, the hybrid system we designed, makes it possible for homomorphic computations to be performed on smaller ciphertext and secret key, providing better performance and lower memory consumption. We make an effort to mitigate side channel leakages within SGX by making the memory access patterns totally independent from the secret information. The evaluation shows that TEEFHE effectively improves the software only FHE schemes in terms of both time and space.

cs.CR↗
arXiv2019

Practical issues of twin-field quantum key distribution

Twin-Field Quantum Key Distribution(TF-QKD) protocol and its variants, such as Phase-Matching QKD(PM-QKD), sending or not QKD(SNS-QKD) and No Phase Post-Selection TF-QKD(NPP-TFQKD), are very promising for long-distance applications. However, there are still some gaps between theory and practice in these protocols. Concretely, a finite-key size analysis is still missing, and the intensity fluctuations are not taken into account. To address the finite-key size effect, we first give the key rate of NPP-TFQKD against collective attack in finite-key size region and then prove it can be against coherent attack. To deal with the intensity fluctuations, we present an analytical formula of 4-intensity decoy state NPP-TFQKD and a practical intensity fluctuation model. Finally, through detailed simulations, we show NPP-TFQKD can still keep its superiority of high key rate and long achievable distance.

quant-ph↗
arXiv2019

Chau-Wang-Wong17 Scheme Is Experimentally More Feasible Than The Six-State Scheme

Recently, Chau et al. [Phys. Rev. A 95, 022311 (2017)] reported a quantum-key-distribution (QKD) scheme using four-dimensional qudits. Surprisingly, as a function of the bit error rate of the raw key, the secret key rate of this scheme is equal to that of the (qubit-based) six-state scheme under one-way classical communication using ideal apparatus in the limit of arbitrarily long raw key length. Here we explain why this is the case in spite of the fact that these two schemes are not linearly related to each other. More importantly, we find that in terms of the four-dimensional dit error rate of the raw key, the Chau et al.'s scheme can tolerate up to 21.6% using one-way classical communications, which is better than the Sheridan and Scarani's scheme [Phys. Rev. A 82, 030301(R) (2010)]. In addition, we argue the experimental advantages of the Chau et al. implementation over the standard six-state scheme and report a corresponding proof-of-principle experiment using passive basis selection with decoy states. We also compare our experiment with the recent high secret key rate implementation of the Sheridan and Scarani's scheme by Islam et al. [Sci. Adv. \text{3}, e1701491].

quant-ph↗
arXiv2019

Twin-field Quantum Key Distribution without Phase Post-Selection

Twin-field quantum key distribution (TF-QKD) protocol and its variants, e.g. phase-matching (PM) QKD and TF-QKD based on sending or not sending, are highly attractive since they are able to overcome the well-known rate-loss limit for QKD protocols without repeater: $R=O(η)$ with $η$ standing for the channel transmittance. However, all these protocols require active phase randomization and post-selection that play an essential role together in their security proof. Counterintuitively, we find that in TF-QKD, beating the rate-loss limit is still possible even if phase randomization and post-selection in the coding mode are both removed, which means our final secure key rate $R=O(\sqrtη)$. Furthermore, our protocol is more feasible in practice and more promising according to its higher final key rate in the valid distance. Our security proof counters collective attack and can also counter coherent attack in asymptotical case

quant-ph↗
arXiv2019

Beating the fundamental rate-distance limit in a proof-of-principle quantum key distribution system

With the help of quantum key distribution (QKD), two distant peers are able to share information-theoretically secure key bits. Increasing key rate is ultimately significant for the applications of QKD in lossy channel. However, it has proved that there is a fundamental rate-distance limit, named linear bound, which limits the performance of all existing repeaterless protocols and realizations. Surprisingly, a recently proposed protocol, called twin-field (TF) QKD can beat linear bound with no need of quantum repeaters. Here, we present the first implementation of TF-QKD protocol and demonstrate its advantage of beating linear bound at the channel distance of 300 km. In our experiment, a modified TF-QKD protocol which does not assume phase post-selection is considered, and thus higher key rate than the original one is expected. After well controlling the phase evolution of the twin fields travelling hundreds of kilometers of optical fibres, the implemented system achieves high-visibility single-photon interference, and allows stable and high-rate measurement-device-independent QKD. Our experimental demonstration and results confirm the feasibility of the TF-QKD protocol and its prominent superiority in long distance key distribution services.

quant-ph↗
arXiv2019

Characterizing high-quality high-dimensional quantum key distribution by state mapping between different degree of freedoms

Quantum key distribution (QKD) guarantees the secure communication between legitimate parties with quantum mechanics. High-dimensional QKD (HDQKD) not only increases the secret key rate but also tolerates higher quantum bit error rate (QBER). Many HDQKD experiments have been realized by utilizing orbital-angular-momentum (OAM) photons as the degree of freedom (DOF) of OAM of the photon is a prospective resource for HD quantum information. In this work we proposed and characterized that a high-quality HDQKD based on polarization-OAM hybrid states can be realized by utilizing state mapping between different DOFs. Both the preparation and measurement procedures of the proof-of-principle verification experiment are simple and stable. Our experiment verified that $(0.60\pm 0.06)\%$ QBER and $1.849\pm 0.008$ bits secret key rate per sifted signal can be achieved for a four-dimensional QKD with the weak coherent light source and decoy state method.

quant-ph↗
arXiv2018

Parameters optimization and real-time calibration of Measurement-Device-Independent Quantum Key Distribution Network based on Back Propagation Artificial Neural Network

The parameters choosing (such as probabilities of choosing X-basis or Z-basis, intensity of signal state and decoy state, etc.) and system calibrating will be more challenging when the number of users of a measurement-device-independent quantum key distribution(MDI-QKD) network becomes larger. At present, people usually use optimization algorithms to search the best parameters. This method can find the optimized parameters accurately but may cost lots of time and hardware resources. It's a big problem in large scale MDI-QKD network. Here, we present a new method, using Back Propagation Artificial Neural Network(BPNN) to predict, rather than searching the optimized parameters. Compared with optimization algorithms, our BPNN is faster and more lightweight, it can save system resources. Another big problem brought by large scale MDI-QKD network is system recalibration. BPNN can support this work in real time, and it only needs to use some discarded data generated from communication process, rather than require us to add additional devices or scan the system

quant-ph↗
arXiv2018

Probing Cosmic Acceleration by Using Model-Independent Parametrizations and Three Kinds of Supernova Statistics Techniques

In this work, we explore the evolution of the dark energy equation of state ω by using Chevalliear-PolarskiLinder (CPL) parametrization and the binned parametrizations. For binned parametrizations, we adopt three methods to choose the redshift interval: I. Ensure that "Δz = const", where Δz is the width of each bin; II.Ensure that "nΔz = const", where n is the number of SNIa in each bin; III. Treat redshift discontinuity points as models parameters, i.e. "free Δz". For observational data, we adopt JLA type Ia supernova (SNIa) samples, SDSS DR12 data, and Planck 2015 distance priors. In particular, for JLA SNIa samples, we consider three statistic techniques: I. Magnitude statistics, which is the traditional method; II. Flux statistics, which reduces the systematic uncertainties of SNIa; III. Improve flux statistics, which can reduce the systematic uncertainties and give tighter constrains at the same time. The results are as follows: (1) For all the cases, ω = -1 is always satisfied at 1σ confidence regions; It means that ΛCDM is still favored by current observations. (2) For magnitude statistics, "free Δz" model will give the smallest error bars; this conclusion does not hold true for flux statistics and improved flux statistic. (3) The improved flux statistic yields a largest present fractional density of matter Ωm; in addition, this technique will give a largest current deceleration parameter q0 , which reveals a universe with a slowest cosmic acceleration.

astro-ph.CO↗
arXiv2018

Comparing dark energy models with current observational data

We make a comparison for thirteen dark energy (DE) models by using current cosmological observations, including type Ia supernova, baryon acoustic oscillations, and cosmic microwave background. To perform a systematic and comprehensive analysis, we consider three statistics methods of SNIa, including magnitude statistic (MS), flux statistic (FS), and improved flux statistic (IFS), as well as two kinds of BAO data. In addition, Akaike information criteria (AIC) and Bayesian information criteria (BIC) are used to assess the worth of each model. We find that: (1) The thirteen models can be divided into four grades by performing cosmology-fits. The cosmological constant model, which is most favored by current observations, belongs to grade one; $α$DE, constant $w$ and generalized Chaplygin gas models belong to grade two; Chevalliear-Polarski-Linder (CPL) parametrization, Wang parametrization, doubly coupled massive gravity, new generalized Chaplygin gas and holographic DE models belong to grade three; agegraphic DE, Dvali-Gabadadze-Porrati, Vacuum metamorphosis and Ricci DE models, which are excluded by current observations, belong to grade four. (2) For parameter estimation, adopting IFS yields the biggest $Ω_m$ and the smallest $h$ for all the models. In contrast, using different BAO data does not cause significant effects. (3) IFS has the strongest constraint ability on various DE models. For examples, adopting IFS yields the smallest value of $Δ$AIC for all the models; in addition, making use of this technique yields the biggest figure of merit for CPL and Wang parametrizations.

astro-ph.CO↗