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

尽管一些理想的量钥匙分发协议被证明了安全，有一些示范，实际的量钥匙分发实现由于一些真实瑕疵被瞎砍。在这些攻击之中，察觉者方面隧道攻击可能是最严肃的。最近，一个测量设备独立人士量钥匙分发协议[Phys。加快。Lett。108 (2012 ) 130503 ] 被建议，所有察觉者方面隧道攻击在这个计划被移开。一个新安全证明基于量信息理论被给的这。偷听者筛的关键位的信息被围住。然后与这跳，最后的安全关键小点率能被获得。

Secret Key Distillation for Continuous Variable Quantum Key Distribution against Gaussian Classical Eve

没有单个光子来源和察觉者，连续的可变的量钥匙分发被期望提供高秘密的关键率，当有效关键蒸馏方法的缺乏在高损失条件下面使它不切实际时。这里我们在场对 Gaussian 古典伊夫的一个 single-bit-reverse-reconciliation 协议，它能与高效率通过实际有瑕疵的错误修正提取秘密钥匙。甚至当传播纤维比 150 km 长时，模拟结果证明这个协议能提取秘密钥匙，它可以做连续可变计划胜过单个光子一个。[从作者抽象]

Dynamics of Quantum State and Effective Hamiltonian with Vector Differential Form of Motion Method

Effective Hamiltonians in periodically driven systems have received widespread attention for realization of novel quantum phases, non-equilibrium phase transition, and Majorana mode. Recently, the study of effective Hamiltonian using various methods has gained great interest. We consider a vector differential equation of motion to derive the effective Hamiltonian for any periodically driven two-level system, and the dynamics of the spin vector are an evolution under the Bloch sphere. Here, we investigate the properties of this equation and show that a sudden change of the effective Hamiltonian is expected. Furthermore, we present several exact relations, whose expressions are independent of the different starting points. Moreover, we deduce the effective Hamiltonian from the high-frequency limit, which approximately equals the results in previous studies. Our results show that the vector differential equation of motion is not affected by a convergence problem, and thus, can be used to numerically investigate the effective models in any periodic modulating system. Finally, we anticipate that the proposed method can be applied to experimental platforms that require time-periodic modulation, such as ultracold atoms and optical lattices.

Ground State and Its Topological Properties of Three-Dimensional Spin-Orbit Coupled Degenerate Fermi Gases

Three-dimensional(3D)degenerate Fermi gases in the presence of spin-orbit coupling,inducing various kinds of physical findings and phenomena,have attracted tremendous attention in these years.We investigate the 3D spin-orbit coupled degenerate Fermi gases in theory and first present the analytic expression of their ground state.Our study provides an innovative perspective into understanding of the topological properties of 3D unconventional superconductors,and describes the topological phase transitions in trivial and topological phase areas.Further,such a system is provided with a richer set of Cooper pairings than traditional superconductors.The dual Cooper pairs with same spin directions emerge and exhibit peculiar behaviors,leading to topological phase transitions.Our study and discussion can be generalized to some other types of unconventional superconductors and areas of optical lattices.

Heteronuclear Magnetisms with Ultracold Spinor Bosonic Gases in Optical Lattices

Motivated by recent realizations of spin-1 NaRb mixtures in the experiments[Phys.Rev.Lett.114,255301(2015);Phys.Rev.Lett.128,223201(2022)],we investigate heteronuclear magnetism in the Mott-insulating regime.Different from the identical mixtures where the boson statistics only admits even parity states from angular momentum composition,for heteronuclear atoms in principle all angular momentum states are allowed,which can give rise to new magnetic phases.While various magnetic phases can be developed over these degenerate spaces,the concrete symmetry breaking phases depend on not only the degree of degeneracy but also the competitions from many-body interactions.We unveil these rich phases using the bosonic dynamical mean-field theory approach.These phases are characterized by various orders,including spontaneous magnetization order,spin magnitude order,singlet pairing order,and nematic order,which may coexist specially in the regime with odd parity.Finally we address the possible parameter regimes for observing these spin-ordered Mott phases.

Gas sensors based on TiO_(2) nanostructured materials for the detection of hazardous gases: A review

Hazardous gases have been strongly associated with being a detriment to human life within the environment The development of a reliable gas sensor with high response and selectivity is of great signifcance for detecting different hazardous gases.TiO_(2) nanomaterials are promising candidates with great potential and excellent per-formance in gas sensor applications,such as hydrogen,acetone,ammonia,and ethanol detection.This review begins with a detailed discussion of the di ferent dimensional morphologies of TiO_(2),whitch affect the gas sensing performance of TiO_(2) sensors.The diverse morphologies of TiO_(2) can easily be tuned by regulating the manufacturing conditions.Meanwhile,they exhibit unique characteristics for detecting gases,including large specific suface area,superior elecron tr ansport rates,extraordinary pemmeability,and active reaction sites,which offer new opportunities to improve the gas sensing properties.In addition,a variety of efforts have been made to functional TiO_(2) nanomaterials to further enhance sensing properties,including TiO_(2)-based composites and light-assisted gas sensors.The enhanced gas sensing mechanisms of multi-component composite nano-materials based on TiO_(2) include loaded noble metals,doped elements,constructed heterojunctions,and com-pounded with other functional materials.Finally,several studies have been summarized to demonstate the compar ative sensing properties of TiO_(2)-based gas sensors.

Spectrum Analysis of a Pulsed Photon Source Generated from Periodically Poled Lithium Niobate

We present a theoretical and experimental study on the bandwidth of parametric down-converted photons generated from periodically poled lithium niobate(PPLN)crystal pumped by a pulsed laser.By comparison of crystals with different lengths and pump beams of different bandwidths,we demonstrate that the bandwidth of down-converted photons will increase for a broader bandwidth of pump pulse and decrease for a longer crystal,but the influence of crystal length will become weaker along with increase of both crystal length and pump pulse bandwidth.Especially under the conditions of our experiment,the bandwidth almost remains unchanged for longer crystals when pumped by a femtosecond laser.This may be helpful for schemes in which pulsed lasers are used to pump PPLN crystals.

Experimental Demonstration of Largeness in Bipartite Entanglement Sudden Death

Quantum coherence is the most distinct feature of quantum mechanics.However,inevitable decoherence processes will finally destroy it and make the"Schrödinger's cat"invisible in our classical world.In this"quantum-to-classical transition",the so-called"largeness"plays a critical role.We experimentally study the largeness phenomena in the bipartite entanglement decay process through a depolarizing channel with two-photon entangled states generated from a spontaneous parametric down-conversion source.Our experiment demonstrates how the speed of entanglement decay and the time when"entanglement sudden death"happens depend on the size of the system exposed to the environment noise.

Measurement of Ultra-Short Single-Photon Pulse Duration with Two-Photon Interference

We proposed a protocol of measuring the duration of ultra-short single-photon pulse with two-photon interference.The pulse duration can be obtained from the width of the visibility of two-photon Hong-Ou-Mandel interference or the indistinguishability of the two photons.Moreover,the shape of a single-photon pulse can be measured with ultra-short single-photon pulses through the two-photon interference.

Generation of Nitrogen-Vacancy Centers in Diamond with Ion Implantation

Nitrogen-vacancy defect color centers are created in a high purity single crystal diamond by nitrogen-ion implantation.Both optical spectrum and optically detected magnetic resonance are measured for these artificial quantum emitters.Moreover,with a suitable mask,a lattice composed of nitrogen-vacancy centers is fabricated.Rabi oscillation driven by micro-waves is carried out to show the quality of the ion implantation and potential in quantum manipulation.Along with compatible standard lithography,such an implantation technique shows high potential in future to make structures with nitrogen-vacancy centers for diamond photonics and integrated photonic quantum chip.

SnO_(2)nanostructured materials used as gas sensors for the detection of hazardous and flammable gases:A review

SnO_(2)has been extensively used in the detection of various gases.As a gas sensing material,SnO_(2)has excellent physical-chemical properties,high reliability,and short adsorption-desorption time.The application of the traditional SnO_(2)gas sensor is limited due to its higher work-temperature,low gas response,and poor selectivity.Nanomaterials can significantly impact gas-sensitive properties due to the quantum size,surface,and small size effects of nanomaterials.By applying nanotechnology to the preparation of SnO_(2),the SnO_(2)nanomaterial-based sensors could show better performance,which greatly expands the application of SnO_(2)gas sensors.In this review,the preparation method of the SnO_(2)nanostructure,the types of gas detected,and the improvements of SnO_(2)gas-sensing performances via elemental modification are introduced as well as the future development of SnO_(2)is discussed.

Active phase compensation of quantum key distribution system

Quantum key distribution (QKD) system must be robust enough in practical communication. Besides birefringence of fiber, system performance is notably affected by phase drift. The Faraday-Michelson QKD system can auto-compensate the birefringence of fiber, but phase shift is still a serious problem in its practical operation. In this paper, the major reason of phase drift and its effect on Faraday- Michel- son QKD system is analyzed and an effective active phase compensation scheme is proposed. By this means, we demonstrate a quantum key distribution system which can stably run over 37-km fiber in practical working condition with the long-time averaged quantum bit error rate of 1.59% and the stan- dard derivation of 0.46%. This result shows that the active phase compensation scheme is suitable to be used in practical QKD systems based on double asymmetric interferometers without additional de- vices and thermal controller.

Multiple stochastic paths scheme on partially-trusted relay quantum key distribution network

Quantum key distribution (QKD) technology provides proven unconditional point-to-point security based on fundamental quantum physics. A QKD network also holds promise for secure multi-user communications over long distances at high-speed transmission rates. Although many schemes have been proposed so far, the trusted relay QKD network is still the most practical and flexible scenario. In reality, the insecurity of certain relay sections cannot be ignored, so to solve the fatal security problems of partially-trusted relay networks we suggest a multiple stochastic paths scheme. Its features are: (i) a safe probability model that may be more practical for real applications; (ii) a multi-path scheme with an upper bound for the overall safe probability; (iii) an adaptive stochastic routing algorithm to generate sufficient different paths and hidden routes. Simulation results for a typical partially-trusted relay QKD network show that this generalized scheme is effective.

A Bright Single-Photon Source from Nitrogen-Vacancy Centers in Diamond Nanowires

Single-photon flux is one of the crucial properties of nitrogen vacancy(NV) centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the single-photon count rate. Through the interaction between tightly confined optical mode in nanowires and NV centers, the single-photon lifetime is much shortened and the collection efficiency is enhanced. As a result, the detected single-photon rate can be at 564 kcps,and the total detection coefficient can be 0.8%,wich is much higher than that in bulk diamond. Such a nanowire single-photon device with high photon flux can be applied to improve the fidelity of quantum computation and the precision of quantum sensors.

Subdiffraction optical manipulation of the charge state of nitrogen vacancy center in diamond

As a potential candidate for quantum computation and metrology,the nitrogen vacancy(NV)center in diamond presents both challenges and opportunities resulting from charge-state conversion.By utilizing different lasers for the photon-induced charge-state conversion,we achieved subdiffraction charge-state manipulation.The charge-state depletion(CSD)microscopy resolution was improved to 4.1 nm by optimizing the laser pulse sequences.Subsequently,the electron spin-state dynamics of adjacent NV centers were selectively detected via the CSD.The experimental results demonstrated that the CSD can improve the spatial resolution of the measurement of NV centers for nanoscale sensing and quantum information.

Ringing phenomenon in silica microspheres

Whispering gallery modes in silica microspheres are excited by a tunable continuous-wave laser throughthe fiber taper.Ringing phenomenon can be observed with high frequency sweeping speed.The thermalnoulmearity in the microsphere can enhance this phenomenon.Our measurement results agree very wellwith the theoretical predictions by the dynamic equation.

Advances in near-infrared avalanche diode single-photon detectors

Avalanche-photodiode-based near-infrared single-photon detectors have seen rapid development in the last two decades because of their enormous internal gain,high sensitivity,fast response,small vol-ume,and ease of integration.The InGaAs/InP near-infrared single-photon detector is the most widely used avalanche diode at present.Its device performance is still being continuously improved through the optimization of device structure and external quenching circuits.This paper analyzes the latest development and application of these InGaAs/InP photodiodes,then briefly re views other near-infrared single-photon detection technologies based on new materials and new mechanisms.

Emerging material platforms for integrated microcavity photonics

Many breakthroughs in technologies are closely associated with the deep understanding and development of new material platforms.As the main material used in microelectronics,Si also plays a leading role in the development of integrated photonics.The indirect bandgap,absence ofχ(2)nonlinearity and the parasitic nonlinear absorptions at the telecom band of Si imposed technological bottlenecks for further improving the performances and expanding the functionalities of Si microcavities in which the circulating light intensity is dramatically amplified.The past two decades have witnessed the burgeoning of the novel material platforms that are compatible with the complementary metal-oxide-semiconductor(COMS)process.In particular,the unprecedented optical properties of the emerging materials in the thin film form have resulted in revolutionary progress in microcavity photonics.In this review article,we summarize the recently developed material platforms for integrated photonics with the focus on chip-scale microcavity devices.The material characteristics,fabrication processes and device applications have been thoroughly discussed for the most widely used new material platforms.We also discuss open challenges and opportunities in microcavity photonics,such as heterogeneous integrated devices,and provide an outlook for the future development of integrated microcavities.