Manipulation and applications of solid-state single quantum systems
固态单量子体系的调控与应用专题编者按
DOI: 10.7498/aps.71.060101
近年来, 随着量子信息科学与技术的进一步发展, 人们对量子信息处理中最基本的信息单元—单量子体系—的操控与探测提出了更高的要求, 例如更高保真度的调控、更长的退相干时间以及更高精度的探测等. 虽然不同体系中单量子态的操控已经取得了很好的进展, 但是离实际应用还有差距, 因此研究不同固态体系中单量子态的操控以及探索其在可扩展化量子信息处理中的应用仍然是目前该领域的重要研究方向. 单量子体系的操控及其与微腔的相互作用为可扩展化的量子调控提供了有效手段, 这对实现未来大规模量子器件及量子信息处理具有重要的意义. 固态单量子体系主要包括单超导比特、单量子点、单缺陷、掺杂单原子以及单分子等体系. 每种体系都有不同的优缺点, 例如基于半导体量子点的单量子体系易于利用微腔耦合进行调控, 可以用超快光学的方法操控, 但是可扩展性差; 金刚石色心是常温下比较稳定的单量子体系, 但是金刚石的掺杂和加工都非常困难; 单分子量子体系利用扫描隧道显微镜可以得到高分辨率成像, 但是其调控和与其他物质相互作用比较困难等.
为进一步促进国内同行的交流, 在《物理学报》编辑部的组织下, 我们邀请了部分活跃在“固态单量子体系的调控与应用研究”领域的中青年专家学者, 组织了本期的专题. 本期专题文章大致分为如下几方面:在半导体量子点方面, 窦秀明和孙宝权报道了金纳米颗粒调控量子点激子自发辐射速率; 魏红介绍了单个金属纳米颗粒和纳米间隙结构与量子发光体的强耦合的动态调控, 并展望了该领域的研究前景; 林星和方伟介绍了基于开放式法布里-珀罗微腔的腔量子电动力学系统的基本特性、制备方法, 以及与固态单量子系统相互作用的研究工作; 张国峰和肖连团综述了单量子点光谱与激子动力学近期的相关研究进展和单量子点光谱未来可能的发展趋势; 许秀来报道了具有反常抗磁行为的量子点荧光的手性传输, 为可扩展化手性量子器件奠定了基础. 在金刚石氮-空位 (NV)色心体系方面, 孔熙和石发展利用单个 NV色心成功探测到金刚石表面纳米尺度水分子分别在固态和液态条件下的核磁信号和固-液相变; 孙方稳介绍了金刚石NV色心的温度特性、测温原理及其在相关领域的应用; 许金时和李传锋理论计算和分析了耦合碳化硅薄膜的光纤腔的性质和特征以及光纤腔耦合色心的增强效果; 荣星综述了金刚石 NV色心体系在量子物理领域取得的重要进展; 刘刚钦介绍了低温、高温、零场、强磁场以及高压强等极端条件下金刚石 NV中心的光学性质和自旋量子传感的进展. 在单分子量子器件与单分子光谱成像方面, 刘俊扬和洪文晶介绍了量子干涉效应的相关理论与预测、实验观测与证实, 以及其在不同单分子器件上的调控作用; 张杨和董振超报道了单个苝四甲酸二酐分子的电致发光特性以及相应的电子-振动跃迁的实空间荧光成像; 赵爱迪综述了基于扫描隧道显微学技术的表面吸附单分子及其相关结构中的量子态研究现状. 在其他单量子体系或者潜在的单子体系方面, 陈宇辉和张向东介绍了掺铒晶体在量子调控方面的应用进展; 孙力玲、 宋友和宋凤麒报道了石墨烯中选择性增强 Kane-Mele型自旋-轨道相互作用; 彭其明和王建浦介绍了有机半导体和卤化物钙钛矿在磁场下的电致发光和光致发光变化, 即发光材料的磁场效应; 丁帅帅和胡文平综述了有机自旋阀中自旋界面的研究进展与问题, 并对有机自旋界面的识别和可控利用进行了展望.
本专题从不同方面描述了固态单量子体系的调控与应用研究的进展, 反映了此领域的一些前沿问题与未来展望, 希望对读者了解此方向有所帮助. 通过本专题, 希望在未来的固态单量子体系调控与应用方向取长补短, 实现优势互补, 促进固态单量子体系领域的蓬勃发展.
DOI: 10.7498/aps.71.060101
近年来, 随着量子信息科学与技术的进一步发展, 人们对量子信息处理中最基本的信息单元—单量子体系—的操控与探测提出了更高的要求, 例如更高保真度的调控、更长的退相干时间以及更高精度的探测等. 虽然不同体系中单量子态的操控已经取得了很好的进展, 但是离实际应用还有差距, 因此研究不同固态体系中单量子态的操控以及探索其在可扩展化量子信息处理中的应用仍然是目前该领域的重要研究方向. 单量子体系的操控及其与微腔的相互作用为可扩展化的量子调控提供了有效手段, 这对实现未来大规模量子器件及量子信息处理具有重要的意义. 固态单量子体系主要包括单超导比特、单量子点、单缺陷、掺杂单原子以及单分子等体系. 每种体系都有不同的优缺点, 例如基于半导体量子点的单量子体系易于利用微腔耦合进行调控, 可以用超快光学的方法操控, 但是可扩展性差; 金刚石色心是常温下比较稳定的单量子体系, 但是金刚石的掺杂和加工都非常困难; 单分子量子体系利用扫描隧道显微镜可以得到高分辨率成像, 但是其调控和与其他物质相互作用比较困难等.
为进一步促进国内同行的交流, 在《物理学报》编辑部的组织下, 我们邀请了部分活跃在“固态单量子体系的调控与应用研究”领域的中青年专家学者, 组织了本期的专题. 本期专题文章大致分为如下几方面:在半导体量子点方面, 窦秀明和孙宝权报道了金纳米颗粒调控量子点激子自发辐射速率; 魏红介绍了单个金属纳米颗粒和纳米间隙结构与量子发光体的强耦合的动态调控, 并展望了该领域的研究前景; 林星和方伟介绍了基于开放式法布里-珀罗微腔的腔量子电动力学系统的基本特性、制备方法, 以及与固态单量子系统相互作用的研究工作; 张国峰和肖连团综述了单量子点光谱与激子动力学近期的相关研究进展和单量子点光谱未来可能的发展趋势; 许秀来报道了具有反常抗磁行为的量子点荧光的手性传输, 为可扩展化手性量子器件奠定了基础. 在金刚石氮-空位 (NV)色心体系方面, 孔熙和石发展利用单个 NV色心成功探测到金刚石表面纳米尺度水分子分别在固态和液态条件下的核磁信号和固-液相变; 孙方稳介绍了金刚石NV色心的温度特性、测温原理及其在相关领域的应用; 许金时和李传锋理论计算和分析了耦合碳化硅薄膜的光纤腔的性质和特征以及光纤腔耦合色心的增强效果; 荣星综述了金刚石 NV色心体系在量子物理领域取得的重要进展; 刘刚钦介绍了低温、高温、零场、强磁场以及高压强等极端条件下金刚石 NV中心的光学性质和自旋量子传感的进展. 在单分子量子器件与单分子光谱成像方面, 刘俊扬和洪文晶介绍了量子干涉效应的相关理论与预测、实验观测与证实, 以及其在不同单分子器件上的调控作用; 张杨和董振超报道了单个苝四甲酸二酐分子的电致发光特性以及相应的电子-振动跃迁的实空间荧光成像; 赵爱迪综述了基于扫描隧道显微学技术的表面吸附单分子及其相关结构中的量子态研究现状. 在其他单量子体系或者潜在的单子体系方面, 陈宇辉和张向东介绍了掺铒晶体在量子调控方面的应用进展; 孙力玲、 宋友和宋凤麒报道了石墨烯中选择性增强 Kane-Mele型自旋-轨道相互作用; 彭其明和王建浦介绍了有机半导体和卤化物钙钛矿在磁场下的电致发光和光致发光变化, 即发光材料的磁场效应; 丁帅帅和胡文平综述了有机自旋阀中自旋界面的研究进展与问题, 并对有机自旋界面的识别和可控利用进行了展望.
本专题从不同方面描述了固态单量子体系的调控与应用研究的进展, 反映了此领域的一些前沿问题与未来展望, 希望对读者了解此方向有所帮助. 通过本专题, 希望在未来的固态单量子体系调控与应用方向取长补短, 实现优势互补, 促进固态单量子体系领域的蓬勃发展.
2022, 71 (6): 067802.
doi: 10.7498/aps.71.20212050
Abstract +
Colloidal semiconductor quantum dots (QDs) have strong light absorption, continuously adjustable narrowband emission, and high photoluminescence quantum yields, thereby making them promising materials for light-emitting diodes, solar cells, detectors, and lasers. Single-QD photoluminescence spectroscopy can remove the ensemble average to reveal the structure information and exciton dynamics of QD materials at a single-particle level. The study of single-QD spectroscopy can provide guidelines for rationally designing the QDs and giving the mechanism basis for QD-based applications. We can also carry out the research of the interaction between light and single QDs on a nanoscale, and prepare QD-based single-photon sources and entangled photon sources. Here, we review the recent research progress of single-QD photoluminescence spectroscopy and exciton dynamics, mainly including photoluminescence blinking dynamics, and exciton and multi-exciton dynamics of single colloidal CdSe-based QDs and perovskite QDs. Finally, we briefly discuss the possible future development trends of single-QD spectroscopy and exciton dynamics.
2022, 71 (6): 063301.
doi: 10.7498/aps.71.20212003
Abstract +
The intramolecular vibronic coupling has a great effect on molecular electronic transitions and associated spectral characteristics, which is a central topic in the study of molecular spectroscopy. In this paper, we investigate the vibronic coupling of a transiently charged state within a single 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) molecule in real space by imaging the spatial distribution of single-molecule electroluminescence via highly localized excitation of tunneling electrons in a plasmonic nanocavity. The electron injections from a scanning tunneling microscope tip into a PTCDA molecule on a silver-supported ultrathin salt layer produce a transient doubly charged molecular anion that emits vibrationally resolved fluorescence. The sub-molecular resolved spectroscopic imaging for the –2 valence transiently charged state shows a two-spot pattern along the molecular short axis for the purely electronic 0-0 transition. However, the observed two-spot orientation for certain anti-symmetric vibronic-state imaging is found to be evidently different from the purely electronic 0-0 transition, rotating 90°, which reflects the change in the transition dipole orientation from along the molecular short axis to the long axis. Such a change directly reveals the occurrence of strong vibronic coupling associated with a large Herzberg-Teller (HT) contribution, which goes beyond the conventional Franck-Condon (FC) picture. Combined with theoretical calculations, the anti-symmetric vibration is found to have a strong dynamic disturbance to the transition density of purely electronic transitions, especially those atoms with large transition densities, which induces a strong transition charge oscillation along the long axis of the molecule and thus leads to a transition dipole along the long axis of the molecule. On the other hand, for vibronic emissions associated with the totally symmetric molecular vibration (such as the v1 (Ag) mode described above), the observed two-spot orientation in the vibronic-state imaging pattern is found to be the same as the purely electronic 0-0 transition, which directly reveals its FC-dominated nature. Notably, the vibration-induced emission associated with HT-dominated contributions (such as the v2 (B3g) mode) is often discussed in the literature by using an intensity borrowing mechanism via the state mixing with other high-lying eigenstates. In the present work, the v2-vibration with B3g symmetry is likely to modulate the zero-order electronic wavefunction of the S1 state in a way to best resemble that of the S2 state (i.e., induce efficient mixing of the electronic excited state S1 with the electronic excited state S2), so that the v2-vibration induced emission seems to borrow intensities from neighboring S2→S0 transitions. Our results provide a new route for the real-space understanding of the microscopic picture for the vibronic coupling within a single molecule in a transiently charged state.
2022, 71 (6): 067804.
doi: 10.7498/aps.71.20211863
Abstract +
As an ideal single-photon source, quantum dots (QDs) can play a unique role in the field of quantum information. Controlling QD exciton spontaneous emission can be achieved by anti-phase coupling between QD exciton dipole field and Au dipole field after QD film has been transferred onto the Si substrate covered by Au nanoparticles. In experiment, the studied InAs/GaAs QDs are grown by molecular beam epitaxy (MBE) on a (001) semi-insulation substrate. The films containing QDs with different GaAs thickness values are separated from the GaAs substrate by etching away the AlAs sacrificial layer and transferring the QD film to the silicon wafer covered by Au nanoparticles with a diameter of 50 nm. The distance D (thickness of GaAs) from the surface of the Au nanoparticles to the QD layer is 10, 15, 19, 25, and 35 nm, separately. A 640-nm pulsed semiconductor laser with a 40-ps pulse length is used to excite the QD samples for measuring QD exciton photoluminescence and time-resolved photoluminescence spectra at 5 K. It is found that when the distance D is 15–35 nm the spontaneous emission rate of exciton is suppressed. And when D is close to 19 nm, the QD spontaneous emission rate decreases to $ ~{10}^{-3} $ , which is consistent with the theoretical calculations. The physical mechanism of long-lived exciton luminescence observed in experiment lies in the fact that Au nanoparticles scatter the light field of the exciton radiation in the QD wetting layer, and the phase of the scattered field is opposite to the phase of the exciton radiation field. Therefore, the destructive interference between the exciton radiation field and scattering field of Au nanoparticles results in long-lived exciton emission observed in experiment.
2022, 71 (6): 066101.
doi: 10.7498/aps.71.20212072
Abstract +
Extreme conditions, such as ultra-low temperatures, high pressures, and strong magnetic fields, are critical to producing and studying exotic states of matter. To measure physical properties under extreme conditions, the advanced sensing schemes are required. As a promising quantum sensor, the diamond nitrogen-vacancy (NV) center can detect magnetic field, electronic field, pressure, and temperature with high sensitivity. Considering its nanoscale spatial resolution and ultra-wide working range, the diamond quantum sensing can play an important role in frontier studies involving extreme conditions. This paper reviews the spin and optical properties of diamond NV center under extreme conditions, including low temperature, high temperature, zero field, strong magnetic fields, and high pressures. The opportunities and challenges of diamond quantum sensing under extreme conditions are discussed. The basic knowledge of spin-based quantum sensing and its applications under extreme conditions are also covered.
2022, 71 (6): 064203.
doi: 10.7498/aps.71.20211803
Abstract +
Quantum information is a rapidly emerging field aiming at combining two of the greatest advances in science and technology of the twentieth century, that is, quantum mechanics and information science. To reliably generate, store, process, and transmit quantum information, diverse systems have been studied. While for specific tasks some of these systems are more suitable than others, no single system can meet all envisioned demands. Erbium doped crystal has optical transition at 1.5 μm and possesses long optical coherence time and spin coherence time, and thus is one of the best candidates in building several essential blocks for quantum information applications. In this review, we summarize the applications of erbium doped crystals in quantum memories, quantum transducers, quantum sources, and quantum manipulations based on erbium-erbium interactions. Finally, the outlooks for near term prospects of the mentioned topics are also given.
2022, 71 (6): 060303.
doi: 10.7498/aps.71.20211797
Abstract +
Single spin color centers in solid materials are one of the promising candidates for quantum information processing, and attract a great deal of interest. Nowadays, single spin color centers in silicon carbide, such as divacancies and silicon vacancies have been developed rapidly, because they not only have similar properties of the NV centers in diamond, but also possess infrared fluorescence that is more favorable for transmission in optical fiber. However, these centers possess week fluorescence with broad spectrum, which prevents some key technologies from being put into practical application, such as quantum key distribution, photon-spin entanglement, spin-spin entanglement and quantum sensing. Therefore, optical resonator is very suitable for coupling centers to filter their spectrum and enhance the fluorescence by Purcell effect. It is very advantageous to use the fiber end face as cavity mirrors, thereby the fiber can provide small cavity volume corresponding to a large enhancement in spin color centers, and collect the fluorescence in cavity simultaneously, which has no extra loss in comparison with other collection methods. In this work, the properties and performance of fiber Fabry-Perot cavity coupling silicon carbide membrane are mainly studied through theoretical calculation. Firstly, some parameters are optimized such as membrane roughness and mirror reflection by calculating the mode of the fiber cavity and enhancing the color centers coupling into the cavity, then analyzing the properties of different modes in cavity, the enhancement effect on cavity coupling color centers, and other relevant factors affecting the cavity coupling color centers. Next, the influences of dominated factor and vibration on the properties of the cavity, the enhancement and outcoupling of centers coupled into the cavity are investigated, and finally the optimal outcoupling efficiency corresponding to different vibration intensities is obtained. These results give direct guidance for the further experimental design and direction for optimization of the fiber cavity coupling color centers.
2022, 71 (6): 067202.
doi: 10.7498/aps.71.20211815
Abstract +
In order to enhance the spin orbit interaction (SOI) in graphene for seeking the dissipationless quantum spin Hall devices, unique Kane-Mele-type SOI and high mobility samples are desired. However, the common external modification of graphene often introduces “extrinsic” Rashba-type SOI, which will destroy the possible topological state, bring a certain degree of impurity scattering and reduce the sample mobility. Here we show that by the EDTA-Dy molecule dressing, the carrier mobility is even improved, and the quantum Hall plateaus are observed more clearly. The Kane-Mele type SOI is mimicked after dressing, which is evidenced by the suppressed weak localization at equal carrier densities and simultaneous Elliot-Yafet spin relaxation. This is attributed to the spin-flexural phonon coupling induced by the enhanced graphene ripples, as revealed by the in-plane magnetotransport measurement.
2022, 71 (6): 067601.
doi: 10.7498/aps.71.20211348
Abstract +
Water is one of the most important substances in the world. It is a crucial issue to study the dynamics of water molecules at interfaces or in the confined systems. In recent years, the emerging magnetic resonance technique based on nitrogen-vacancy (NV) center has allowed us to observe the nanoscale nuclear magnetic signal and temperature simultaneously. Here we succeed in measuring the nuclear magnetic resonance (NMR) signals of nanoscale solid and liquid water on diamond surface by NV center, and observing the solid-liquid phase transition of these nano-water by temperature control. This work demonstrates that the nano-NMR technique based on NV centers can probe the dynamics behavior of nanoscale materials effectively, providing a new way for studying the nanoscale confined systems.
2022, 71 (6): 060304.
doi: 10.7498/aps.71.20211808
Abstract +
In the field of quantum physics, quantum control is essential. Precise and efficient quantum control is a prerequisite for the experimental research using quantum systems, and it is also the basis for applications such as in quantum computing and quantum sensing. As a solid-state spin system, the nitrogen-vacancy (NV) center in diamond has a long coherence time at room temperature. It can be initialized and read out by optical methods, and can achieve universal quantum control through the microwave field and radio frequency fields. It is an excellent experimental platform for studying quantum physics. In this review, we introduce the recent results of quantum control in NV center and discuss the following parts: 1) the physical properties of the NV center and the realization method of quantum control, 2) the decoherence mechanism of the NV center spin qubit, and 3) the application of single-spin quantum control and relevant research progress.
2022, 71 (6): 060201.
doi: 10.7498/aps.71.20211970
Abstract +
The interaction between light and matter has attracted much attention not only for fundamental research but also for applications. The open Fabry-Perot cavity provides an excellent platform for such a study due to strong optical confinement, spectral and spatial and tunability, and the feasibility of optical fiber integration. In this review, first, the basic properties of open Fabry-Perot cavities and the fabrication techniques are introduced. Then recent progress of weak coupling, strong coupling and bad emitter regimes is discussed. Finally, the challenges to and perspectives in this respect are presented.
2022, 71 (6): 060701.
doi: 10.7498/aps.71.20212324
Abstract +
Single molecular systems are typical quantum confinement systems, which have rich electronic states, photon states and spin states due to their discrete energy levels, localized orbitals and diverse chemical structures. The states determined by quantum mechanics in these molecular systems make it possible to serve as great physical entities for future quantum information technology. The detection and manipulation of quantum states on a single molecule scale are beneficial to the bottom-up construction of quantum devices. Owing to the highly limited spatial localization of single molecular systems, it is difficult to accurately address and manipulate them with conventional macroscopic characterization methods. Scanning tunneling microscope (STM) is such a powerful tool that it can achieve high-resolution real-space imaging as well as spectroscopic investigation, with the ability to in-situ manipulating the individual atoms or molecules. It can also work jointly with various near-field or external field characterization techniques, making it a most important technique for precisely detecting and manipulating quantum properties at a single molecule level. In this paper, we review recent research progress of quantum states of surface-supported single molecules and relevant structures based on scanning tunneling microscopy. We start from the methods for the synthesis of molecular structures with desired quantum states, and then we review the recent advances in the local spin states for single molecular systems and the optical properties of single molecules serving as a single-photon source. An emerging family of molecular nanographene systems showing intriguing topological properties and magnetic properties is also reviewed. In the last part, we summarize the research progress made recently and prospect the future development of the quantum states at a single molecular level.
2022, 71 (6): 067801.
doi: 10.7498/aps.71.20211858
Abstract +
In order to realize scalable and integrated quantum photonic networks, various functional devices are highly desired. Strip waveguides with unidirectional transmission function have a wide range of applications in devices such as single-photon diodes, transistors and deterministic quantum gate devices. In this work, the separation of circularly polarized light is achieved by exciting a quantum dot light source in a central region of a waveguide at a low temperature of 4.2 K by using a confocal microscope system. By applying a magnetic field with Faraday configuration (along with the quantum dot growth direction), the spin-momentum locking effect in the waveguide is verified. Both forward shift and reverse shift of different values of output photon energy are demonstrated to show the unidirectional transmission of the waveguide. The chiral transmission of quantum dot with anomalous diamagnetic behavior is achieved in experiment, leading to a wider range of wavelength tuning for chrial transmission in a single waveguide. This paper provides a basis for investigating the chiral quantum devices in a wide wavelength range and expands the applications of waveguides in the field of optical quantum information.
2022, 71 (6): 068502.
doi: 10.7498/aps.71.20211872
Abstract +
Magnetic field effects (MFEs) are used to describe the changes of the photophysical properties (including photoluminescence, electroluminescence, injectedcurrent, photocurrent, etc.) when materials and devices are subjected to the external magnetic field. The MFEs in non-magnetic luminescent materials and devices were first observed in organic semiconductor. In the past two decades, the effects have been studied extensively as an emerging physical phenomenon, and also used as a unique experimental method to explore the processes such as charge transport, carrier recombination, and spin polarization in organic semiconductors. Recent studies have found that the MFEs can also be observed in metal halide perovskites with strong spin-orbital coupling. Besides, for expanding the research domain of MFEs, these findings can also be utilized to study the physical mechanism in metal halide perovskites, and then provide an insight into the improving of the performance of perovskite devices. In this review, we focus on the magnetic field effects on the electroluminescence and photoluminescence changes of organic semiconductors and halide perovskites. We review the mainstream of theoretical models and representative experimental phenomena which have been found to date, and comparatively analyze the luminescence behaviors of organic semiconductors and halide perovskites under magnetic fields. It is expected that this review can provide some ideas for the research on the MFEs of organic semiconductors and halideperovskites, and contribute to the research of luminescence in organic materials and halideperovskites.
2022, 71 (6): 067301.
doi: 10.7498/aps.71.20211900
Abstract +
In cavity quantum electrodynamics, when the interaction between quantum emitter and cavity mode is strong enough to overcome the mean decay rate of the system, it will enter into a strong coupling regime, thereby forming part-light part-matter polariton states. Strong coupling can serve as a promising platform for room temperature Bose-Einstein condensation, polariton lasing, single photon nonlinearity, quantum information, etc. Localized surface plasmons supported by single metal nanostructures possess extremely small mode volume, which is favorable for realizing strong coupling. Moreover, the nanoscale dimensions of plasmonic structures can facilitate the miniaturization of strong coupling systems. Here, the research progress of strong plasmon-exciton coupling between single metal nanoparticles/nanogaps and quantum emitters is reviewed. The theory background of strong coupling is first introduced, including quantum treatment, classical coupled oscillator model, as well as the analytical expressions for scattering and photoluminescence spectra. Then, strong coupling between different kinds of plasmonic nanostructures and quantum emitters is reviewed. Single metal nanoparticles, nanoparticle dimers, and nanoparticle-on-mirror structures constitute the most typical plasmonic nanostructures. The nanogaps in the latter two systems can highly concentrate electromagnetic field, providing optical nanocavities with smaller mode volume than single nanoparticles. Therefore, the larger coupling strength can be achieved in the nanogap systems, which is conducive to strong coupling at the single-exciton level. In addition, the active tuning of strong coupling based separately on thermal, electrical and optical means are reviewed. The energy and oscillator strength of the excitons in transition metal dichalcogenide (TMDC) monolayers are dependent on temperature. Therefore, the strong coupling can be tuned by heating or cooling the system. The excitons in TMDC monolayers can also be tuned by electrical gating, enabling electrical control of strong coupling. Optically tuning the quantum emitters provides another way to actively control the strong coupling. Overall, the research on active tuning of strong plasmon-exciton coupling is still very limited, and more investigations are needed. Finally, this review is concluded with a short summary and the prospect of this field.
2022, 71 (6): 067201.
doi: 10.7498/aps.71.20211786
Abstract +
Spintronics are attractive to the utilization in next-generation quantum-computing and memory. Compared with inorganic spintronics, organic spintronics not only controls the spin degree-of-freedom but also possesses advantages such as chemical tailorability, flexibility, and low-cost fabrication process. Besides, the organic spin valve with a sandwich configuration that is composed of two ferromagnetic electrodes and an organic space layer is one of the classical devices in organic spintronics. Greatly enhanced or inversed magnetoresistance (MR) sign appearing in organic spin valve is induced by the unique interfacial effect an organic semiconductor/ferromagnetic interface. The significant enhancement or inversion of MR is later proved to be caused by the spin-dependent hybridization between molecular and ferromagnetic interface, i.e., the spinterface. The hybridization is ascribed to spin-dependent broadening and shifting of molecular orbitals. The spinterface takes place at one molecular layer when attaching to the surface of ferromagnetic metal. It indicates that the MR response can be modulated artificially in a specific device by converting the nature of spinterface. Despite lots of researches aiming at exploring the mechanism of spinterface, several questions need urgently to be resolved. For instance, the spin polarization, which is difficult to identify and observe with the surface sensitive technique and the inversion or enhancement of MR signal, which is also hard to explain accurately. The solid evidence of spinterface existing in real spintronic device also needs to be further testified. Besides, the precise manipulation of the MR sign by changing the nature of spinterface is quite difficult. According to the above background, this review summarizes the advance in spinterface and prospects future controllable utilization of spinterface. In Section 2, we introduce the basic principle of spintronic device and spinterface. The formation of unique spinterface in organic spin valve is clarified by using the difference in energy level alignment between inorganic and organic materials. Enhancement and inversion of MR sign are related to the broadening and shifting of the molecular level. In Section 3, several examples about identification of spinterface are listed, containing characterization by surface sensitive techniques and identification in real working devices. In Section 4 some methods about the manipulation of spinterface are exhibited, including modulation of ferroelectric organic barrier, interface engineering, regulation of electronic phase separation in ferromagnetic electrodes, etc. Finally, in this review some unresolved questions in spintronics are given, such as multi-functional and room-temperature organic spin valve and improvement of the spin injection efficiency. Spinterface is of great importance for both scientific research and future industrial interest in organic spintronics. The present study paves the way for the further development of novel excellent organic spin valves.
2022, 71 (6): 067303.
doi: 10.7498/aps.71.20211819
Abstract +
The quantum interference effect in single-molecule devices is a phenomenon in which electrons are coherently transported through different frontier molecular orbitals with multiple energy levels, and the interference will occur between different energy levels. This phenomenon results in the increase or decrease of the probability of electron transmission in the electrical transport of the single-molecule device, and it is manifested in the experiment when the conductance value of the single-molecule device increases or decreases. In recent years, the use of quantum interference effects to control the electron transport in single-molecule device has proved to be an effective method, such as single-molecule switches, single-molecule thermoelectric devices, and single-molecule spintronic devices. In this work, we introduce the related theories of quantum interference effects, early experimental observations, and their regulatory role in single-molecule devices.
2022, 71 (6): 060302.
doi: 10.7498/aps.71.20211822
Abstract +
Temperature is the most intuitive and widespread in various physical quantities. Violent changes in temperature usually implies the appearing of fluctuations in physical properties of an object. Therefore, temperature is often an important indicator. With the development of science and technology, the scales in many fields are being more and more miniaturized. However, there are no mature temperature measurement systems in the case where the spatial scale is less than 10 μm. In addition to the requirement for spatial resolution, the sensor ought to exert no dramatic influence on the object to be measured. The nitrogen vacancy (NV) center in diamond is a stable luminescence defect. The measurements of its spectrum and spin state can be used to obtain the information about physical quantities near the color center, such as temperature and electro-magnetic field. Owing to its stable chemical properties and high thermal conductivity, the NV center can be applied to the noninvasive detection for nano-scale researches. It can also be used in the life field because it is non-toxic to cells. Moreover, combined with different techniques, such as optical fiber, scanning thermal microscopy, NV center can be used to measure the local temperatures in different scenarios. This review focuses on the temperature properties, the method of measuring temperature, and relevant applications of NV centers.
