High-Speed Quantum Transducer with a Single-Photon Emitter in a 2D Resonator

Quantum transducers can transfer quantum information between different systems. Microwave–optical photon conversion is important for future quantum networks to interconnect remote superconducting quantum computers with optical fibers. Here, a high-speed quantum transducer based on a single-photon emitter in an atomically thin membrane resonator, that can couple single microwave photons to single optical photons, is proposed. The 2D resonator is a freestanding van der Waals heterostructure (which may consist of hexagonal boron nitride, graphene, or other 2D materials) that hosts a quantum emitter. The mechanical vibration (phonon) of the 2D resonator interacts with optical photons by shifting the optical transition frequency of the single-photon emitter with strain or the Stark effect. The mechanical vibration couples to microwave photons by shifting the resonant frequency of an LC circuit that includes the membrane. Thanks to the small mass of the 2D resonator, both the single-photon optomechanical coupling strength and the electromechanical coupling strength can reach the strong coupling regime. This provides a way for high-speed quantum state transfer between a microwave photon, a phonon, and an optical photon.     

光学微盘腔与三能级量子点系统中的模耦合研究

用一种全量子理论方法研究了波导、光学微盘腔与三能级量子点耦合系统的动力学过程,求出其耦合后的透射模和反射模的解析解. 由于微腔表面粗糙引起反向散射,在微腔内形成两简并回音壁耦合共振模,其耦合率为β;量子点的两激发态分别以耦合率g₁,g₂与回音壁耦合共振模产生耦合. 在实数空间里,得出透射光谱和反射光谱的数值解,这些三能级模型结果比二能级模型结果更接近真实光学微盘腔系统,能更好地显示耦合系统的动力学特性. 关键词： 模耦合 光学微盘腔 三能级量子点 全量子理论     

Optical absorption and electromagnetically induced transparency in semiconductor quantum well driven by intense terahertz field

An approach for solving the excitonic absorption in a semiconductor quantum well driven by an intense terahertz field is presented.The formalism relies on the stationary single-photon Schro¨dinger equation in the full quantum mechanical framework.The optical absorption dynamics in both weak and strong couplings are discussed and compared.The excitonic absorption spectra show the Autler-Townes doublets for the resonance terahertz field,a replica peak for the non-resonance terahertz field,and the electromagnetically induced transparency phenomenon for modulating the decay rate of the second electron state in the weak coupling.In particular,the electromagnetically induced transparency phenomenon window range is discussed.In the strong coupling region,the multi-order energy level resonance splitting due to the strong optical field is found.There are three(non-resonance terahertz field) or four(resonance terahertz field) peaks in the optical absorption spectra.This work provides a simple and convenient approach to deal with the optical absorption in the exciton system.     

玻璃中两能级隧道态耦合态及其对低频声吸收的影响

讨论了在声子作用下，两能级隧道态耦合态激发和退激发规律，并用此理论解释低温低频声吸收规律 关键词：     

基于光量子态避错及容错传输的量子通信

量子通信以量子态为信息载体在远距离的通信各方之间传递信息,因此量子态的传输和远距离共享是量子通信的首要步骤.信道噪声不仅会影响通信效率还可能被窃听者利用从而威胁通信安全,对抗信道噪声是实现安全高效量子通信亟需解决的问题.本文介绍基于光量子态的两类对抗信道噪声的实用方法——量子态的避错传输和容错的量子通信,包括对抗噪声的基本原理和两种方法的代表性方案,并从资源消耗和可操作性的角度分析了方案的实用价值.     

Strong Coupling Optomechanics Mediated by a Qubit in the Dispersive Regime

Cavity optomechanics represents a flexible platform for the implementation of quantum technologies, useful in particular for the realization of quantum interfaces, quantum sensors and quantum information processing. However, the dispersive, radiation–pressure interaction between the mechanical and the electromagnetic modes is typically very weak, harnessing up to now the demonstration of interesting nonlinear dynamics and quantum control at the single photon level. It has already been shown both theoretically and experimentally that if the interaction is mediated by a Josephson circuit, one can have an effective dynamics corresponding to a huge enhancement of the single-photon optomechanical coupling. Here we analyze in detail this phenomenon in the general case when the cavity mode and the mechanical mode interact via an off-resonant qubit. Using a Schrieffer–Wolff approximation treatment, we determine the regime where this tripartite hybrid system behaves as an effective cavity optomechanical system in the strong coupling regime.     

Spectral Characterization of Couplings in a Mixed Optomechanical Model *

Abstract:We study the spectrum of single-photon emission and scattering in a mixed optomechanical model which consists of both linear and quadratic optomechanical interactions. The spectra are calculated based on the exact long-time solutions of the single-photon emission and scattering processes in this system. We find that there exist some phonon sideband peaks in the spectra and there are some sub peaks around the phonon sideband peaks under proper parameter conditions. The correspondence between the spectral features and the optomechanical interactions is confirmed, and the optomechanical coupling strengths can be inferred by analyzing the resonance peaks and dips in the spectra.     

Selection Rules for Multiple Quantum NMR Excitation in Solids: Derivation from Time-Reversal Symmetry and Comparison with Simulations and C NMR Experiments

New derivations of selection rules for excitation and detection of multiple quantum coherences in coupled spin-1/2 systems are presented. The selection rules apply to experiments in which the effective coupling Hamiltonian used for multiple quantum excitation is both time-reversal invariant and time-reversible by a phase shift of the radiofrequency pulse sequence that generates the effective couplings. The selection rules are shown to be consequences of time-reversal invariance and time-reversibility and otherwise independent of the specific form of the effective coupling Hamiltonian. Numerical simulations of multiple quantum NMR signal amplitudes and experimental multiple quantum excitation spectra are presented for the case of a multiply ¹³C-labeled helical polypeptide. The simulations and experiments confirm the selection rules and demonstrate their impact on multiple quantum ¹³C NMR spectra in this biochemically relevant case.     

Plasmonic-photonic cavity for high-efficiency single-photon blockade

The generation and manipulation of single photons are crucial in advanced quantum technologies, such as quantum communication and quantum computation devices. High-purity single photons can be generated from classical light using the single-photon blockade(1 PB). However, the efficiency and purity are exclusive in 1 PB, which hinders its practical applications. Here, we show that the resonantly coupled plasmonic-photonic cavity can boost the efficiency of single-photon generation by more than three orders of magnitude compared with that of all-dielectric microcavity. This significant improvement is attributed to two new mechanisms of atom-microcavity coupling after introducing the plasmonic cavity: the formation of a quasi-bound state and the transition to the nonreciprocal regime, due to the destructive interference between the coupling pathways and the nonzero relative phase of the closed-loop coupling, respectively. The quasi-bound state has a relatively small decaying, while its effective coupling strength is significantly enhanced. Suppressing the dissipative component of the effective atom-microcavity coupling in the nonreciprocal regime can further improve single-photon performance, particularly without temporal oscillations. Our study demonstrates the possibility of enhancing the intrinsically low efficiency of 1 PB in low excitation regime, and unveils the novel light-matter interaction in hybrid cavities.     

一种广义三模腔光机械系统的相干完美吸收与透射

提出了一种广义的三模式腔光机械系统,系统的中间是一个反射率为100%的可移动的全反射机械振子,两侧均由一个部分透射的固定光学腔镜构成.其中两个光学腔由一束较强的控制场和一束较弱的信号场驱动与同一个机械振子实现耦合.较弱的信号场将会被该系统完全吸收而不产生任何能量输出,并且当相干完美吸收产生时,输入信号场的能量将由两个腔场和机械模共同分担;较弱的输入信号场由一个腔完美透视到另一个腔而不产生任何的能量损耗.分析与数值结果显示,在不同参数机制下,在该三模光机械系统中可以实现相干完美吸收、相干完美透射和相干完美合成的量子现象.此外,改变腔与腔之间的耦合度,可以实现输出探测场在相干完美吸收和相干完美透射之间转换;通过简单的相位调制,可以实现探测场左腔-右腔的输出和输入方向的互换.这些动态控制在量子信息网络可用来构造光子开关、光子路由、光子交换机等一些特殊功能的光子学器件.     

Integrated and compact fiber-coupled single-photon system based on nitrogen-vacancy centers and gradient-index lenses

A fiber-coupled single-photon system is presented. Gradient-index lenses are utilized for single-photon collection and fiber coupling of a nitrogen-vacancy defect center in a nanodiamond. Integrated filter technology separates excitation and laser light. Therefore, the system is ultracompact with 120 mm(3) in dimension as no bulky free beam optics are used. The commercial availability of all components and their simple assembly allows the implementation of a low-cost single-photon system, possibly approaching single-photon count rates of 500 kcts/s.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

电子自旋辅助实现光子偏振态的量子纠缠浓缩

量子纠缠浓缩可以将非最大的纠缠态转变为最大纠缠态,提高量子通信的安全性.本文基于圆偏振光和量子点-腔系统的相互作用,用一个单光子作为连接远距离纠缠光子对的桥梁,在理想条件下实现了光子偏振纠缠态的浓缩.计算结果显示,这个纠缠浓缩方案在考虑耦合强度和腔泄漏的情况下也可以保持较高的保真度,而且不需要知道部分纠缠态的初始信息,也不必重复执行纠缠浓缩过程.这不仅提高了量子纠缠浓缩的安全性,也有助于通过消耗最少的量子资源来实现高效的量子信息处理.     

Quantum properties of nonclassical states generated by an optomechanical system with catalytic quantum scissors

A scheme is proposed to investigate the non-classical states generated by a quantum scissors device (QSD) operating on the the cavity mode of an optomechanical system. When the catalytic QSD acts on the cavity mode of the optomechanical system, the resulting state contains only the vacuum, single-photon and two-photon states depending upon the coupling parameter of the optomechanical system as well as the transmission coefficients of beam splitters (BSs). Especially, the output state is just a class of multicomponent cat state truncations at time t=2π by choosing the appropriate value of coupling parameter. We discuss the success probability of such a state and the fidelity between the output state and input state via QSD. Then the linear entropy is used to investigate the entanglement between the two subsystems, finding that QSD operation can enhance their entanglement degree. Furthermore, we also derive the analytical expression of the Wigner function (WF) for the cavity mode via QSD and numerically analyze the WF distribution in phase space at time t=2π. These results show that the high non-classicality of output state can always be achieved by modulating the coupling parameter of the optomechanical system as well as the transmittance of BSs.     

Heralded amplification of single-photon entanglement with polarization feature

Heralded noiseless amplification is beneficial in overcoming transmission photon loss in a noisy quantum channel. We propose a single-photon-assisted heralded noiseless amplification protocol of the singlephoton entanglement (SPE), where the single-photon qubit has an arbitrary unknown polarization feature. We focus on both the complete and partial photon loss during the transmission process. After the amplification, the parties can recover the pure less-entangled SPE into a maximally entangled SPE and increase its fidelity. Moreover, the polarization feature of the single-photon qubit will be well preserved and not be leaked. Our protocol can be realized under our current experimental condition. Based on the features above, our protocol may be useful in the quantum secure communication schemes that encode information in the polarization degree of freedom of photons.     

Improving the purity of heralded single-photon sources through spontaneous parametric down-conversion process

The high-purity single-photon source plays an important role in the field of quantum information. Usually, it is generated through spontaneous parametric down-conversion process. In this paper, we investigate and summarize a few approaches on obtaining single-photon sources with a high purity using either PPKTP or PPLN nonlinear crystals. Moreover, we present improved schemes to increase the purity based on existing work, corresponding applicable conditions and procedures are discussed and analyzed. Besides, we carry out numerical simulations and show that nearly perfect purity can be reached even without using any filters. Therefore, this work might provide valuable references for the generation and application of high purity single-photon sources.     

氧化锌量子点和碳量子点及其复合物的制备与发光性能的研究

采用溶胶凝胶方法和水热法制备了水溶性荧光氧化锌量子点(Zn O-QDs)和碳量子点(C-QDs),其量子效率分别达到38%和61%。基于所合成的Zn O-QDs和C-QDs制备了氧化锌和碳量子点复合物(Zn O/CQDs),并分别对其发光特性进行了研究。透射电镜(TEM)图像表明,所合成的Zn O-QDs和碳量子点尺寸分布在3~6 nm之间,分散均匀。光致发光光谱表明,Zn O-QDs和碳量子点的发光峰中心分别位于540 nm和450 nm,两者发光峰的最佳激发波长为370 nm和350 nm。通过调整Zn O-QDs和C-QDs的体积比,所制备的Zn O/C-QDs能够实现荧光光谱的连续可调,并产生了白色荧光。     

InAs/GaAs量子点1.3 μm单光子发射特性

采用双层耦合量子点的分子束外延生长技术生长了InAs/GaAs量子点样品,把量子点的发光波长成功地拓展到1.3 μm.采用光刻的工艺制备了直径为3 μm的柱状微腔,提高了量子点荧光的提取效率.在低温5 K下,测量得到量子点激子的荧光寿命约为1 ns;单量子点荧光二阶关联函数为0.015,显示单量子点荧光具有非常好的单光子特性;利用迈克耳孙干涉装置测量得到单光子的相干时间为22 ps,对应的谱线半高全宽度为30 μeV,且荧光谱线的线型为非均匀展宽的高斯线型.     

Hyperentanglement-assisted hyperdistillation for hyper-encoding photon system

In quantum information processing, the quality of photon system is decreased by the inevitable interaction with environment, which will greatly reduce the efficiency and security of quantum information processing. In this paper, we propose hyperentanglement-assisted hyperdistillation schemes to guarantee the quality of hyper-encoding photon system based on the method of quantum hyper-teleportation, which can increase the success probability of hyperdistillation and reduce the resource consumption. First, we propose a hyperentanglement-assisted single-photon hyperdistillation (HASPHD) scheme for polarization and spatial qubits to get rid of the vacuum state component caused by transmission loss, whose success probability can achieve the optimal one by increasing the efficiency of quantum hyper-teleportation. Subsequently, we present two hyperentanglement-assisted hyperentanglement distillation (HAHED) schemes for photon system to protect hyperentanglement from both transmission loss and quantum channel noise, which can recover the less-entangled mixed state to maximally hyperentangled state for known-parameter and unknown-parameter cases with high success probability and low resource consumption. In these hyperdistillation schemes, the influence of imperfect effects of optical elements can be largely decreased by the quantum hyper-teleportation method. These characters make the hyperentanglement-assisted hyperdistillation schemes have potential application prospects in practical quantum information processing.     

Low energy excitations in amorphous metals

The low temperature properties of amorphous metals pertinent to the existence of low energy excitations are reviewed. In an introductory section, the currently accepted model for low energy excitations, i.e. the model of two level systems (TLS), is discussed. The treatment of amorphous metals focuses on the specific heat C, thermal conductivity κ, ultrasonic properties and electrical resistivity ?. Measurements of C and κ are often performed on amorphous superconductors in order to exclude the effect of conduction electrons. The TLS density of states and the TLS-phonon coupling in these materials as determined from C and κ respectively are surprisingly close to values for insulating glasses. Ultrasonic experiments carried out mostly on normal amorphous metals reveal a strongly enhanced TLS relaxation rate with respect to insulators. This can be attributed to TLS-electron coupling. The effect of this coupling on ? is uncertain at present. In order to obtain more insight into the microscopic origin of TLS in metallic and insulating glasses some examples of TLS in crystalline disordered solids are discussed. Finally, some formal analogies are drawn between spin glasses and real glasses.