本文提出一种与 ENZ 材料强耦合的 68 nm 等离激元超表面，通过调控二阶非线性极化率张量，在无需额外元件的情况下高效产生偏振纠缠 Bell 态。
摘要：
偏振纠缠光子对源对于量子通信、量子计算和量子成像等多种量子技术至关重要。然而，复杂偏振纠缠量子态的产生长期以来受到天然非线性晶体可用非线性极化率张量的限制，需要繁琐且复杂的装置来进行额外的相干叠加或后选择。在本研究中，我们提出并通过实验演示了一种利用人工工程化超材料平台的纳米级偏振纠缠光子对源。该平台基于与 ε-near-zero（ENZ，介电常数近零）材料强耦合的等离激元超表面。通过在泵浦光和信号/闲频光波长处精确设计共振，并利用 ENZ 效应提供的场增强，厚度仅为 68 nm 的超表面的光子对产生效率得到显著提升。更值得注意的是，ENZ 超表面平台支持对系统的各向异性二阶非线性极化率张量进行灵活调控，从而能够直接控制光子对的偏振态，无需额外元件即可产生偏振纠缠 Bell 态。我们的方法为在紧凑平台上同时实现光子对产生和量子态工程开辟了新途径。
英文摘要：
Polarization-entangled photon pair sources are essential for diverse quantum technologies, such as quantum communication, computation, and imaging. However, the generation of complex polarization-entangled quantum states has long been constrained by the available nonlinear susceptibility tensor of natural nonlinear crystals, necessitating a cumbersome and intricate setup for additional coherent superposition or post-selection. In this study, we introduce and experimentally demonstrate a nanoscale polarization-entangled photon pair source utilizing an artificially-engineered metamaterial platform. This platform is based on a plasmonic metasurface that is strongly coupled to an epsilon-near-zero (ENZ) material. By precisely engineering resonances at both pump and signal/idler wavelengths, and leveraging the field enhancement provided by the ENZ effect, the photon pair generation efficiency of the 68-nm-thick metasurface is significantly boosted. More notably, the ENZ metasurface platform facilitates versatile manipulation of the system's anisotropic second-order nonlinear susceptibility tensor, enabling direct control over the polarization states of the photon pairs, which leads to the generation of a polarization-entangled Bell state without the need for additional components. Our approach opens a new avenue for the simultaneous photon pair generation and quantum state engineering in a compact platform.
Fully reconfigurable metasurfaces would enable new classes of optical devices that provide unprecedented control of electromagnetic beamforms. The principal challenge for achieving reconfigurability is the need to generate large tunability of subwavelength, low-Q metasurface resonators. Here, we demonstrate large refractive index tuning can be efficiently facilitated at mid-infrared wavelengths using novel temperature-dependent control over free-carrier refraction. In doped InSb we demonstrate nearly two-fold increase in the electron effective mass leading to a positive refractive index shift …
Optical properties of a metasurface which can be considered a monolayer of two classical uniaxial metamaterials, parallel-plate and nanorod arrays, are investigated. It is shown that such metasurface acts as an ultimately thin sub-50 nm wave plate. This is achieved via an interplay of epsilon-near-zero and epsilon-near-pole behavior along different axes in the plane of the metasurface allowing for extremely rapid phase difference accumulation in very thin metasurface layers. These effects are shown to not be disrupted by non-locality and can be applied to the design of ultrathin wave plates, P…
Plasmonics and metamaterials have recently been shown to allow the control and interaction with non-classical states of light, a rather counterintuitive finding given the high losses typically encountered in these systems. Here, we demonstrate a range of functionalities that are allowed with correlated and entangled photons that are used to illuminate multiple, overlaid patterns on plasmonic metasurfaces. Correlated photons allow to nonlocally determine the pattern that is imaged or, alternatively to un-scramble an image that is otherwise blurred. Entangled photons allow a more important funct…
We propose a tunable coherent perfect absorber based on ultrathin nonlinear metasurfaces. The nonlinear metasurface is made of plasmonic nanoantennas coupled to an epsilon-near-zero material with a large optical nonlinearity. The coherent perfect absorption is achieved by controlling the relative phases of the input beams. We show that the optical response of the nonlinear metasurface can be tuned from a complete to a partial absorption by changing the intensity of the pump beam. The proposed nonlinear metasurface can be used to design optically tunable thermal emitters, modulators, and sensor…
The unique properties of the emerging photonic materials - conducting nitrides and oxides - especially their tailorability, large damage thresholds, and the so-called epsilon-near-zero (ENZ) behavior, have enabled novel photonic phenomena spanning optical circuitry, tunable metasurfaces, and nonlinear optical devices. This work explores direct control of the optical properties of polycrystalline titanium nitride (TiN) and aluminum-doped zinc oxide (AZO) by tailoring the film thickness, and their potential for ENZ-enhanced photonic applications. We demonstrate that TiN-AZO bilayers act as Ferre…
Metasurfaces consisting of nano-scale structures are underpinning new physical principles for the creation and shaping of quantum states of light. Multi-photon states that are entangled in spatial or angular domains are an essential resource for quantum imaging and sensing applications, however their production traditionally relies on bulky nonlinear crystals. We predict and demonstrate experimentally the generation of spatially entangled photon pairs through spontaneous parametric down-conversion from a metasurface incorporating a nonlinear thin film of lithium niobate. This is achieved throu…
Femtosecond all-optical polarization manipulation of harmonic generation in an anisotropic strongly coupled plasmon-epsilon-near-zero metasurface
Key Laboratory for Physical Electronics and Devices of the Ministry of Education and Shaanxi Key Lab of Information Photonic Technique, School of Electronic Science and Engineering, Xi’an Jiaotong University（教育部光电技术与器件重点实验室、陕西省信息光子技术重点实验室，西安交通大学电子科学与工程学院）
We develop a concept of metasurface-assisted ghost imaging for non-local discrimination between a set of polarization objects. The specially designed metasurfaces are incorporated in the imaging system to perform parallel state transformations in general elliptical bases of quantum-entangled or classically-correlated photons. Then, only four or fewer correlation measurements between multiple metasurface outputs and a simple polarization-insensitive bucket detector after the object can allow for the identification of fully or partially transparent polarization elements and their arbitrary orien…
Nonlinear light sources are central to a myriad of applications, driving a quest for their miniaturisation down to the nanoscale. In this quest, nonlinear metasurfaces hold a great promise, as they enhance nonlinear effects through their resonant photonic environment and high refractive index, such as in high-index dielectric metasurfaces. However, despite the sub-diffractive operation of dielectric metasurfaces at the fundamental wave, this condition is not fulfilled for the nonlinearly generated harmonic waves, thereby all nonlinear metasurfaces to date emit multiple diffractive beams. Here,…
Tensor-Engineered Van der Waals NbOCl2 Resonant Metasurface for Polarization-entangled Bell State Generation
CAS Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology（中国科学院纳米科技标准化与计量重点实验室，国家纳米科学中心）；Frontiers Science Center for New Organic Matter, Tianjin Key Lab for Rare Earth Materials and Applications, Renewable Energy Conversion and Storage Center (RECAST), School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University（前沿科学中心新有机物质，天津市稀土材料与应用重点实验室，可再生能源转换与存储中心（RECAST），南开大学材料科学与工程学院，先进材料国家研究院）；CAS Key Laboratory of Quantum Information, University of Science and Technology of China（中国科学院量子信息重点实验室，中国科学技术大学）；School of Materials Science and Engineering, Peking University（北京大学材料科学与工程学院）；School of Materials Science and Engineering, Nanyang Technological University（南洋理工大学材料科学与工程学院）；School of Electrical and Electronic Engineering, Nanyang Technological University（南洋理工大学电气与电子工程学院）；University of Chinese Academy of Sciences（中国科学院大学）；Hefei National Laboratory, University of Science and Technology of China（合肥国家实验室，中国科学技术大学）；Beijing Key Laboratory of Advanced Micro- and Nanoscale Light Source Materials and Devices, Peking University（北京先进微纳光源材料与器件重点实验室，北京大学）
Dual-polarization control of broadband nonreciprocal thermal radiation by combining local and nonlocal metasurfaces
The University of Hong Kong（香港大学）；State Key Laboratory of Optical Quantum Materials, The University of Hong Kong（香港大学光学量子材料国家重点实验室）；Institute of Engineering Thermophysics, MOE Key Laboratory for Power Machinery and Engineering, School of Mechanical Engineering, Shanghai Jiao Tong University（上海交通大学机械工程学院动力机械工程教育部重点实验室工程热物理研究所）；Department of Electrical and Computer Engineering, National University of Singapore（新加坡国立大学电气与计算机工程系）；Key Laboratory of Terahertz Solid State Technology, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences（中国科学院上海微系统与信息技术研究所太赫兹固态技术重点实验室）；National Engineering Research Center of Electromagnetic Radiation Control Materials, University of Electronic Science and Technology of China（电子科技大学电磁辐射控制材料国家工程研究中心）
Preservation of the entangled state of a quantum system is relevant in quantum applications. However, the preservation of entangled states is constrained due to the energy dissipation of the quantum system arising from the environment. As a result, the design of the environment seen by quantum bits is relevant due to its relation to the final state of the quantum system. This work presents the concurrence measure of entanglement between two qubits coupled to a rolled-up epsilon-near-zero (ENZ) waveguide reservoir consisting of an alternating layer of metal and dielectric. Our numerical calcula…
Optical metasurfaces open new avenues for precise wavefront control of light for integrated quantum technology. Here, we demonstrate a hybrid integrated quantum photonic system that is capable to entangle and disentangle two-photon spin states at a dielectric metasurface. By interfering single-photon pairs at a nanostructured dielectric metasurface, a path-entangled two-photon NOON state with circular polarization is generated that exhibits a quantum HOM interference visibility of 86 $\pm$ 4%. Furthermore, we demonstrate nonclassicality and phase sensitivity in a metasurface-based interferomet…
All-dielectric optical metasurfaces are a workhorse in nano-optics due to both their ability to manipulate light in different degrees of freedom and their excellent performance at light frequency conversion. Here, we demonstrate first-time generation of photon pairs via spontaneous parametric-down conversion in lithium niobate quantum optical metasurfaces with electric and magnetic Mie-like resonances at various wavelengths. By engineering the quantum optical metasurface, we tailor the photon-pair spectrum in a controlled way. Within a narrow bandwidth around the resonance, the rate of pair pr…
Monolayer transition-metal dichalcogenides (TMDCs) present high second-order optical nonlinearity, which is extremely desirable for, e.g., frequency conversion in nonlinear photonic devices. On the other hand, the atomic thickness of 2D materials naturally leads to low frequency converted intensities, highlighting the importance to design structures that enhance the nonlinear response for practical applications. A number of methods to increase the pump electric field at the 2D material has been reported, relying on complex plasmonic and/or metasurface structures. Here, we take advantage of the…
Quantum state engineering, the cornerstone of quantum photonic technologies, mainly relies on spontaneous parametric down-conversion and four-wave mixing, where one or two pump photons decay into a photon pair. Both these nonlinear effects require momentum conservation (i.e., phase-matching) for the participating photons, which strongly limits the versatility of the resulting quantum states. Nonlinear metasurfaces, due to their subwavelength thickness, relax this constraint and extend the boundaries of quantum state engineering. Here, we generate entangled photons via spontaneous parametric do…
Quantum Phase Gradient Imaging Using a Nonlocal Metasurface System
ARC Centre of Excellence for Transformative Meta-Optical Systems (TMOS), Department of Electronic Materials Engineering, Research School of Physics, The Australian National University（澳大利亚国立大学）；Institute of Quantum Precision Measurement, State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Physics and Optoelectronic Engineering, Shenzhen University（深圳大学）；Institute of Solid State Physics, Abbe Center of Photonics, Friedrich-Schiller-University Jena（耶拿弗里德里希·席勒大学）；TMOS, Department of Electrical and Electronic Engineering, School of Physics, University of Melbourne（墨尔本大学）；Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena（耶拿弗里德里希·席勒大学）；Fraunhofer Institute for Applied Optics and Precision Engineering IOF（弗劳恩霍夫应用光学和精密工程研究所）
Spontaneous parametric down-conversion (SPDC) is one of the most versatile nonlinear optical techniques for the generation of entangled and correlated single-photon pairs. However, it suffers from very poor efficiency leading to extremely weak photon generation rates. Here we propose a plasmonic metasurface design based on silver nanostripes combined with a bulk lithium niobate (LiNbO3) crystal to realize a new scalable, ultrathin, and efficient SPDC source. By coinciding fundamental and higher order resonances of the metasurface with the generated signal and idler frequencies, respectively, t…
Miniaturised entangled photon sources are highly demanded for the development of integrated quantum photonics. Since the invention of subwavelength optical metasurfaces and their successes at replacing bulky optical components, the possibility of implementing entangled photon sources on such devices is actively investigated. Here, as a first step towards the development of quantum optical metasurfaces (QOM), we demonstrate photon pair generation via spontaneous parametric down-conversion (SPDC) from subwavelength films. We achieved photon pair generation with a high coincidence-to-accidental r…
Quantum field theory predicts that a spatially homogeneous but temporally varying medium will excite photon pairs out of the vacuum state. However, this important theoretical prediction lacks experimental verification due to the difficulty in attaining the required non-adiabatic and large amplitude changes in the medium. Recent work has shown that in epsilon-near-zero (ENZ) materials it is possible to optically induce changes of the refractive index of the order of unity, in femtosecond timescales. By studying the quantum field theory of a spatially homogeneous, time-varying ENZ medium, we the…
Metamaterials have been a major research area for more than two decades now, involving artificial structures with predesigned electromagnetic properties constructed from deep subwavelength building blocks. They have been used to demonstrate a wealth of fascinating phenomena ranging from negative refractive index and epsilon-near-zero to cloaking, emulations of general relativity effects, and super-resolution imaging, to name a few. In the past few years, metamaterials have been suggested as a new platform for quantum optics, and several pioneering experiments have already been carried out with…
We discuss the conclusions that can be drawn on a recent experimental micro-macro entanglement test [F. De Martini, F. Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008). The system under investigation is generated through optical parametric amplification of one photon belonging to an entangled pair. The adopted entanglement criterion makes it possible to infer the presence of entanglement before losses, that occur on the macrostate, under a specific assumption. In particular, an a priori knowledge of the system that generates the micro-macro pair is necessary to exclude a class of…
Temporal modulation of the quantum vacuum through fast motion of a neutral body or fast changes of its optical properties is known to promote virtual into real photons, the so-called dynamical Casimir effect. Empowering modulation protocols with spatial control could enable to shape the spectral, spatial, spin, and entanglement properties of the emitted photon pairs. Space-time quantum metasurfaces have been proposed as a platform to realize this physics via modulation of their optical properties. Here, we report the mechanical analog of this phenomenon by considering systems whose lattice str…
Single-Image Entanglement Verification with Spatially Encoded Measurement Contexts
University of Ottawa（渥太华大学）；National Research Council of Canada（加拿大国家研究委员会）；Sorbonne Université（索邦大学）；CNRS, Institut des NanoSciences de Paris, INSP（法国国家科学研究中心，巴黎纳米科学研究所）；School of Physics & Astronomy, University of Glasgow（格拉斯哥大学物理与天文学学院）；Institute for Quantum Studies, Chapman University（查普曼大学量子研究所）
