Countermeasure against blinding attack for single-photon detectors in quantum key distribution

Quantum key distribution(QKD),rooted in quantum mechanics,offers information-theoretic security.However,practi-cal systems open security threats due to imperfections,notably bright-light blinding attacks targeting single-photon detectors.Here,we propose a concise,robust defense strategy for protecting single-photon detectors in QKD systems against blinding attacks.Our strategy uses a dual approach:detecting the bias current of the avalanche photodiode(APD)to defend against con-tinuous-wave blinding attacks,and monitoring the avalanche amplitude to protect against pulsed blinding attacks.By integrat-ing these two branches,the proposed solution effectively identifies and mitigates a wide range of bright light injection attempts,significantly enhancing the resilience of QKD systems against various bright-light blinding attacks.This method forti-fies the safeguards of quantum communications and offers a crucial contribution to the field of quantum information security.

New approach to Q-P (P-Q) ordering of quantum mechanical operators and its applications

In this paper, we introduce a new way to obtain the Q-P （P-Q） ordering of quantum mechanical operators, i.e., from the classical correspondence of Q-P （P-Q） ordered operators by replacing q and p with coordinate and momentum operators, respectively. Some operator identities are derived concisely. As for its applications, the single （two-） mode squeezed operators and Fresnel operator are examined. It is shown that the classical correspondence of Fresnel operator’s Q-P （P-Q） ordering is just the integration kernel of Fresnel transformation. In addition, a new photo-counting formula is constructed by the Q-P ordering of operators.

Imaging assessment of photosensitizer emission induced by radionuclide-derived Cherenkov radiation using charge-coupled device optical imaging and long-pass filters

BACKGROUND Radionuclides produce Cherenkov radiation(CR),which can potentially activate photosensitizers(PSs)in phototherapy.Several groups have studied Cherenkov energy transfer to PSs using optical imaging;however,cost-effectively identifying whether PSs are excited by radionuclide-derived CR and detecting fluorescence emission from excited PSs remain a challenge.Many laboratories face the need for expensive dedicated equipment.AIM To cost-effectively confirm whether PSs are excited by radionuclide-derived CR and distinguish fluorescence emission from excited PSs.METHODS The absorbance and fluorescence spectra of PSs were measured using a microplate reader and fluorescence spectrometer to examine the photo-physical properties of PSs.To mitigate the need for expensive dedicated equipment and achieve the aim of the study,we developed a method that utilizes a chargecoupled device optical imaging system and appropriate long-pass filters of different wavelengths(manual sequential application of long-pass filters of 515,580,645,700,750,and 800 nm).Tetrakis(4-carboxyphenyl)porphyrin(TCPP)was utilized as a model PS.Different doses of copper-64(^(64)CuCl_(2))(4,2,and 1 mCi)were used as CR-producing radionuclides.Imaging and data acquisition were performed 0.5 h after sample preparation.Differential image analysis was conducted by using ImageJ software(National Institutes of Health)to visually evaluate TCPP fluorescence.RESULTS The maximum absorbance of TCPP was at 390-430 nm,and the emission peak was at 670 nm.The CR and CRinduced TCPP emissions were observed using the optical imaging system and the high-transmittance long-pass filters described above.The emission spectra of TCPP with a peak in the 645-700 nm window were obtained by calculation and subtraction based on the serial signal intensity(total flux)difference between^(64)CuCl_(2)+TCPP and^(64)CuCl_(2).Moreover,the differential fluorescence images of TCPP were obtained by subtracting the^(64)CuCl_(2)image from the^(64)CuCl_(2)+TCPP image.The experimental results considering different^(64)CuCl_(2)doses showed a dosedependent trend.These results demonstrate that a bioluminescence imaging device coupled with different longpass filters and subtraction image processing can confirm the emission spectra and differential fluorescence images of CR-induced TCPP.CONCLUSION This simple method identifies the PS fluorescence emission generated by radionuclide-derived CR and can contribute to accelerating the development of Cherenkov energy transfer imaging and the discovery of new PSs.

Simulating a Chern Insulator with𝐶C=±2 on Synthetic Floquet Lattice

The synthetic Floquet lattice,generated by multiple strong drives with mutually incommensurate frequencies,provides a powerful platform for quantum simulation of topological phenomena.In this study,we propose a 4-band tight-binding model of the Chern insulator with a Chern number𝐶=±2 by coupling two layers of the half Bernevig–Hughes–Zhang lattice and subsequently mapping it onto the Floquet lattice to simulate its topological properties.To determine the Chern number of our Floquet-version model,we extend the energy pumping method proposed by Martin et al.[2017 Phys.Rev.X 7041008]and the topological oscillation method introduced by Boyers et al.[2020 Phys.Rev.Lett.125160505],followed by numerical simulations for both methodologies.The simulation results demonstrate the successful extraction of the Chern number using either of these methods,providing an excellent prediction of the phase diagram that closely aligns with the theoretical one derived from the original bilayer half Bernevig–Hughes–Zhang model.Finally,we briefly discuss a potential experimental implementation for our model.Our work demonstrates significant potential for simulating complex topological matter using quantum computing platforms,thereby paving the way for constructing a more universal simulator for non-interacting topological quantum states and advancing our understanding of these intriguing phenomena.

Classical-Noise-Free Sensing Based on Quantum Correlation Measurement

Quantum sensing,using quantum properties of sensors,can enhance resolution,precision,and sensitivity of imaging,spectroscopy,and detection.An intriguing question is:Can the quantum nature(quantumness)of sensors and targets be exploited to enable schemes that are not possible for classical probes or classical targets?Here we show that measurement of the quantum correlations of a quantum target indeed allows for sensing schemes that have no classical counterparts.As a concrete example,in the case that the second-order classical correlation of a quantum target could be totally concealed by non-stationary classical noise,the higher-order quantum correlations can single out a quantum target from the classical noise background,regardless of the spectrum,statistics,or intensity of the noise.Hence a classical-noise-free sensing scheme is proposed.This finding suggests that the quantumness of sensors and targets is still to be explored to realize the full potential of quantum sensing.New opportunities include sensitivity beyond classical approaches,non-classical correlations as a new approach to quantum many-body physics,loophole-free tests of the quantum foundation,et cetera.

Evolution of quantum states via Weyl expansion in dissipative channel

Based on the Weyl expansion representation of Wigner operator and its invariant property under similar transformation,we derived the relationship between input state and output state after a unitary transformation including Wigner function and density operator.It is shown that they can be related by a transformation matrix corresponding to the unitary evolution.In addition,for any density operator going through a dissipative channel,the evolution formula of the Wigner function is also derived.As applications,we considered further the two-mode squeezed vacuum as inputs,and obtained the resulted Wigner function and density operator within normal ordering form.Our method is clear and concise,and can be easily extended to deal with other problems involved in quantum metrology,steering,and quantum information with continuous variable.

Continuous-variable quantum key distribution based on photon addition operation

It is shown that the non-Gaussian operations can not only be used to prepare the nonclassical states, but also to improve the entanglement degree between Gaussian states. Thus these operations are naturally considered to enhance the performance of continuous variable quantum key distribution(CVQKD), in which the non-Gaussian operations are usually placed on the right-side of the entangled source. Here we propose another scheme for further improving the performance of CVQKD with the entangled-based scheme by operating photon-addition operation on the left-side of the entangled source.It is found that the photon-addition operation on the left-side presents both higher success probability and better secure key rate and transmission distance than the photon subtraction on the right-side, although they share the same maximal tolerable noise. In addition, compared to both photon subtraction and photon addition on the right-side, our scheme shows the best performance and the photon addition on the right-side is the worst.

A Security Proof of Measurement Device Independent Quantum Key Distribution： From the View of Information Theory

Although some ideal quantum key distribution protocols have been proved to be secure, there have been some demonstrations that practical quantum key distribution implementations were hacked due to some real-life imperfections. Among these attacks, detector side channel attacks may be the most serious. Recently, a measurement device independent quantum key distribution protocol [Phys. Rev. Lett. 108 （2012） 130503] was proposed and all detector side channel attacks are removed in this scheme. Here a new security proof based on quantum information theory is given. The eavesdropper＇s information of the sifted key bits is bounded. Then with this bound, the final secure key bit rate can be obtained.

Symmetry-Assisted Protection and Compensation of Hidden Spin Polarization in Centrosymmetric Systems

It was recently noted that in certain nonmagnetic centrosymmetric compounds,spin–orbit interactions couple each local sector that lacks inversion symmetry,leading to visible spin polarization effects in the real space,dubbed“hidden spin polarization(HSP)”.However,observable spin polarization of a given local sector suffers interference from its inversion partner,impeding material realization and potential applications of HSP.Starting from a single-orbital tight-binding model,we propose a nontrivial way to obtain strong sector-projected spin texture through the vanishing hybridization between inversion partners protected by nonsymmorphic symmetry.The HSP effect is generally compensated by inversion partners near the Г point but immune from the hopping effect around the boundary of the Brillouin zone.We further summarize 17 layer groups that support such symmetry-assisted HSP and identify hundreds of quasi-2D materials from the existing databases by first-principle calculations,among which a group of rare-earth compounds LnIO(Ln=Pr,Nd,Ho,Tm,and Lu)serves as great candidates showing strong Rashba-and Dresselhaus-type HSP.Our findings expand the material pool for potential spintronic applications and shed light on controlling HSP properties for emergent quantum phenomena.

Proposal on Tunneling Effect between Quantum Hall States

In the integer and fractional quantum Hall effects, the electric current flows through a thin layer under the strong magnetic field. The diagonal resistance becomes very small at integer and specific fractional filling factors where the electron scatterings are very few. Accordingly the coherent length is large and therefore a tunneling effect of electrons may be observed. We consider a new type of a quantum Hall device which has a narrow potential barrier in the thin layer. Then the electrons flow with tunneling effect through the potential barrier. When the oscillating magnetic field is applied in addition to the constant field, the voltage steps may appear in the curve of voltage V versus electric current I. If the voltage steps are found in the experiment, it is confirmed that the 2D electron system yields the same phenomenon as that of the ac-Josephson effect in a superconducting system. Furthermore the step V is related to the transfer charge Q as V = (hf)/Q where f is the frequency of the oscillating field and h is the Planck constant. Then the detection of the step V determines the transfer charge Q. The ratio Q/e (e is the elementary charge) clarifies the origin of the transfer charge. Many conditions are required for us to observe the tunneling phenomenon. The conditions are examined in details in this article.

Extension of Linear Response Regime in Weak-Value Amplification Technique

The achievable precision of parameter estimation plays a significant role in evaluating a strategy of metrology.In practice,one may employ approximations in a theoretical model development for simplicity,which,however,will cause systematic error and lead to a loss of precision.We derive the error of maximum likelihood estimation in the weak-value amplification technique where the linear approximation of the coupling parameter is used.We show that this error is positively related to the coupling strength and can be effectively suppressed by improving the Fisher information.Considering the roles played by weak values and initial meter states in the weak-value amplification,we also point out that the estimation error can be decreased by several orders of magnitude by averaging the estimations resulted from different initial meter states or weak values.These results are finally illustrated in a numerical example where an extended linear response regime to the parameter is observed.

Induction heating for desorption of surface contamination for high-repetition laser-driven carbon-ion acceleration

This study reports the first experimental demonstration of surface contamination cleaning from a high-repetition supply of thin-tape targets for laser-driven carbon-ion acceleration.The adsorption of contaminants containing protons,mainly water vapor and hydrocarbons,on the surface of materials exposed to low vacuum(>10^(−3)Pa)suppresses carbon-ion acceleration.The newly developed contamination cleaner heats a 5-μm-thick nickel tape to over 400℃in 100 ms by induction heating.In the future,this heating method could be scaled to laserdriven carbon-ion acceleration at rates beyond 10 Hz.The contaminant hydrogen is eliminated from the heated nickel surface,and a carbon source layer—derived from the contaminant carbon—is spontaneously formed by the catalytic effect of nickel.The species of ions accelerated from the nickel film heated to various temperatures have been observed experimentally.When the nickel film is heated beyond∼150℃,the proton signal considerably decreases,with a remarkable increase in the number and energy of carbon ions.The Langmuir adsorption model adequately explains the temperature dependence of desorption and re-adsorption of the adsorbed molecules on a heated target surface,and the temperature required for proton-free carbon-ion acceleration can be estimated.

Chiral Dirac Fermion in a Collinear Antiferromagnet

In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU(2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb_(3)S_(6), paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.

Twistronics and moiréexcitonic physics in van der Waals heterostructures

Heterostructures composed of two-dimensional van der Waals(vdW)materials allow highly controllable stacking,where interlayer twist angles introduce a continuous degree of freedom to alter the electronic band structures and excitonic physics.Motivated by the discovery of Mott insulating states and superconductivity in magic-angle bilayer graphene,the emerging research fields of“twistronics”and moiréphysics have aroused great academic interests in the engineering of optoelectronic properties and the exploration of new quantum phenomena,in which moirésuperlattice provides a pathway for the realization of artificial excitonic crystals.Here we systematically summarize the current achievements in twistronics and moiréexcitonic physics,with emphasis on the roles of lattice rotational mismatches and atomic registries.Firstly,we review the effects of the interlayer twist on electronic and photonic physics,particularly on exciton properties such as dipole moment and spin-valley polarization,through interlayer interactions and electronic band structures.We also discuss the exciton dynamics in vdW heterostructures with different twist angles,like formation,transport and relaxation processes,whose mechanisms are complicated and still need further investigations.Subsequently,we review the theoretical analysis and experimental observations of moirésuperlattice and moirémodulated excitons.Various exotic moiréeffects are also shown,including periodic potential,moiréminiband,and varying wave function symmetry,which result in exciton localization,emergent exciton peaks and spatially alternating optical selection rule.We further introduce the expanded properties of moirésystems with external modulation factors such as electric field,doping and strain,showing that moirélattice is a promising platform with high tunability for optoelectronic applications and in-depth study on frontier physics.Lastly,we focus on the rapidly developing field of correlated electron physics based on the moirésystem,which is potentially related to the emerging quantum phenomena.

Geometric phase helical PSF for simultaneous orientation and 3D localization microscopy

The 3D location and dipole orientation of light emitters provide essential information in many biological,chemical,and physical systems.Simultaneous acquisition of both information types typically requires pupil engineering for 3D localization and dual-channel polarization splitting for orientation deduction.Here we report a geometric phase helical point spread function for simultaneously estimating the 3D position and dipole orientation of point emitters.It has a compact and simpler optical configuration compared to polarization-splitting techniques and yields achromatic phase modulation in contrast to pupil engineering based on dynamic phase,showing great potential for single-molecule orientation and localization microscopy.

Quantum squeezing induced nonreciprocal phonon laser

Phonon lasers or coherent amplifications of mechanical oscillations are powerful tools for fundamental studies on coherent acoustics and hold potential for diverse applications,ranging from ultrasensitive force sensing to phononic information processing.Here,we propose the use of an optomechanical resonator coupled to a nonlinear optical resonator for directional phonon lasing.We find that by pumping the nonlinear optical resonator,directional optical squeezing can occur along the pump direction.As a result,we can achieve the directional mechanical gain using directional optical squeezing,thereby leading to nonreciprocal phonon lasing with a well-tunable directional power threshold.Our work proposes a feasible way to build nonreciprocal phonon lasers with various nonlinear optical media,which are important for a wide range of applications,such as directional acoustic amplifiers,invisible sound sensing or imaging,and one-way phononic networks.

Tunable quantum dots in monolithic Fabry-Perot microcavities for high-performance single-photon sources

Cavity-enhanced single quantum dots(QDs)are the main approach towards ultra-high-performance solid-state quantum light sources for scalable photonic quantum technologies.Nevertheless,harnessing the Purcell effect requires precise spectral and spatial alignment of the QDs’emission with the cavity mode,which is challenging for most cavities.Here we have successfully integrated miniaturized Fabry-Perot microcavities with a piezoelectric actuator,and demonstrated a bright single-photon source derived from a deterministically coupled QD within this microcavity.Leveraging the cavity-membrane structures,we have achieved large spectral tunability via strain tuning.On resonance,a high Purcell factor of~9 is attained.The source delivers single photons with simultaneous high extraction efficiency of 0.58,high purity of 0.956(2)and high indistinguishability of 0.922(4).Together with its compact footprint,our scheme facilitates the scalable integration of indistinguishable quantum light sources on-chip,therefore removing a major barrier to the development of solid-state quantum information platforms based on QDs.

Quantum weak force sensing with squeezed magnomechanics

Cavity magnomechanics,exhibiting remarkable experimental tunability,rich magnonic nonlinearities,and compatibility with various quantum systems,has witnessed considerable advances in recent years.However,the potential benefits of using cavity magnomechanical(CMM)systems in further improving the performance of quantum-enhanced sensing for weak forces remain largely unexplored.Here we show that,by squeezing the magnons,the performance of a quantum CMM sensor can be significantly enhanced beyond the standard quantum limit(SQL).We find that,for comparable parameters,two orders of magnitude enhancement in the force sensitivity can be achieved in comparison with the case without magnon squeezing.Moreover,we obtain the optimal parameter regimes of homodyne angle for minimizing the added quantum noise.Our findings provide a promising approach for highly tunable and compatible quantum force sensing using hybrid CMM devices,with potential applications ranging from quantum precision measurements to quantum information processing.

Fabrication of ultra-high strength magnesium alloys over 540 MPa with low alloying concentration by double continuously extrusion

We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JDBM-2.8Nd,which increases with the Nd concentration.The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250℃and the elongation is about 3.7%.Moreover,the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing.However,when extruded under the same conditions,the alloy with a higher alloying contents exhibits better tensile properties.

Extremal Entangled Four-Qubit Pure States with Respect to Multiple Entropy Measures

Four-qubit entanglement has been investigated using a recent proposed entanglement measure, multiple entropy measures （MEMS）. We have performed optimization for the nine different families of states of four-qubit system. Some extremal entangled states have been found.