Li Yang, Ziyi Yang, Huaxing Xu
Even and odd vector modes in optical fibers are represented with linear combinations of orbital angular momentum modes, and considered as single-photon spin-orbit entangled states. It renders generating such states with fiber structures possible.
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We demonstrate a novel polarization-entangled photon-pair source based on standard birefringent polarization-maintaining optical fiber. The source consists of two stretches of fiber spliced together with perpendicular polarization axes, and has the potential to be fully fiber-based, with all bulk optics replaced with in-fiber equivalents. By modelling the temporal walk-off in the fibers, we implement compensation necessary for the photon creation processes in the two stretches of fiber to be indistinguishable. Our source subsequently produces a high quality entangled state having (92.2 \pm 0.2…
Entanglement in the spatial degrees of freedom of photons is an interesting resource for quantum information. For practical distribution of such entangled photons it is desireable to use an optical fiber, which in this case has to support multiple transverse modes. Here we report the use of a hollow-core photonic crystal fiber to transport spatially entangled qubits.
We suggest the generation of photon pairs in a thermally induced nonlinear periodically-poled silica fiber by spontaneous parametric down-conversion. Photons are generated directly in eigenstates of optical angular momentum. Photons in a pair can be entangled in these states as well as in frequencies. We identify suitable spatial and polarization modes giving an efficient nonlinear interaction. By changing the pump field properties both narrow- and broad-band down-converted fields can be obtained.
In this letter, we report a compact, low-power laser diode-pumped, all-fiber polarization-entangled photon pair source based on periodically-poled silica fiber technology. The all-fiber source offers room-temperature, alignment-free, turn-key operation, with low power consumption, and is packaged into a fanless, portable enclosure. It features a broad biphoton spectrum of more than 100nm with a concurrence that is greater than 0.96 for polarization entanglement. The source is stable over at least 10 hours of continuous operation, achieving coincidence-to-accidental ratios of more than 2000 con…
Integrated photonic circuits offer the possibility for complex quantum optical experiments in higher-dimensional photonic systems. However, the advantages of integration and scalability can only be fully utilized with the availability of a source for higher-dimensional entangled photons. Here, a novel fiber integrated source for path-entangled photons in the telecom band at 1.55\mum using only standard fiber technology is presented. Due to the special design the source shows good scalability towards higher-dimensional entangled photonic states (quNits), while path entanglement offers direct co…
The ultimate goal of quantum information science is to build a global quantum network, which enables quantum resources to be distributed and shared between remote parties. Such quantum network can be realized by all fiber elements, which takes advantage of low transmission loss,low cost, scalable and mutual fiber communication techniques such as dense wavelength division multiplexing. Therefore high quality entangled photon sources based on fibers are on demanding for building up such kind of quantum network. Here we report multiplexed polarization and timebin entanglement photon sources based…
High coherent frequency-entangled photons at telecom band are critical in quantum information protocols and quantum tele-communication. While photon pairs generated by spontaneous parametric down-conversion in nonlinear crystal or modulation instability in optical fiber exhibit random fluctuations, making the photons distinguishable among consecutive roundtrips. Here, we demonstrate a frequency-entangled photons based on parametric instability in an active fiber ring cavity, where periodic modulation of dispersion excites parametric resonance. The characteristic wave number in parametric insta…
Tunable fiber source of entangled UV-C and infrared photons
该研究利用充氙气单环光子晶体光纤中的四波混频，生成了紫外与红外光谱范围内的纠缠光子对，通过调节气压实现了高达170 THz的频率调谐，为紫外光谱学和传感开辟了新途径。
The capacity of optical communication channels can be increased by space division multiplexing in structured optical fibers. Radial core optical fibers allows for the propagation of twisted light--eigenmodes of orbital angular momentum, which have attracted considerable attention for high-dimensional quantum information. Here we study the generation of entangled photons that are tailor-made for coupling into ring core optical fibers. We show that the coupling of photon pairs produced by parametric down-conversion can be increased by close to a factor of three by pumping the non-linear crystal …
Polarization-entangled photon pair generation based on two scalar scattering processes of the vector four photon scattering has been demonstrated experimentally in high nonlinear microstructure fiber with birefringence. By controlling the pump polarization state, polarization-entangled Bell states can be realized. It is provides a simple way to realize efficient and compact fiber based polarization-entangled photon pair sources.
We propose a new all-fiber source of polarization-entangled photon pairs for quantum communications. Fiber birefringence is compensated using Faraday rotator mirror, resulting in enhanced stability against random polarization drifts compared to existing schemes.
High fidelity distribution of triggered polarization-entangled telecom photons via a 36km intra-city fiber network
本文通过双向偏振保持量子频率转换，将量子点发射的偏振纠缠光子对从780纳米转换至电信波长，并在36公里城域光纤网络中实现高保真分发，验证了纠缠保持及反向转换，为量子网络和量子存储器接口奠定基础。
We report on theoretical and experimental demonstration of high-efficiency coupling of two-photon entangled states produced in the nonlinear process of spontaneous parametric down conversion into a single-mode fiber. We determine constraints for the optimal coupling parameters. This result is crucial for practical implementation of quantum key distribution protocols with entangled states.
We present a consistent multimode theory that describes the coupling of single photons generated by collinear Type-I parametric down-conversion into single-mode optical fibers. We have calculated an analytic expression for the fiber diameter which maximizes the pair photon count rate. For a given focal length and wavelength, a lower limit of the fiber diameter for satisfactory coupling is obtained.
In this paper, the generation of polarization entangled photon pairs at 1.5 μm is experimentally demonstrated utilizing a polarization maintaining all-fiber loop, consisting of a piece of commercial polarization maintaining fiber and a polarization beam splitter/combiner with polarization maintaining fiber pigtails. A quantum state tomography measurement is performed to analyze the entanglement characteristic of the generated quantum state. In the experiment, a polarization entangled Bell state is generated with a entanglement fidelity of 0.97+/-0.03 and a purity of 0.94+/-0.03 demonstrating t…
We experimentally demonstrate the generation of a three-photon discrete-energy-entangled W state using multi-photon-pair generation by spontaneous four-wave mixing in an optical fiber. We show that by making use of prior information on the photon source we can verify the state produced by this source without resorting to frequency conversion.
We have studied the purity of entangled photon-pairs generated in a dispersion-shifted fiber at various temperatures. Two-photon interference with visibility > 98% is observed at 77K, without subtraction of the background Raman photons.
We report the generation of polarization entangled photon pairs in the 1550-nm wavelength band using spontaneous four-wave mixing in a dispersion-shifted fiber loop. The use of the fiber-loop configuration made it possible to generate polarization entangled states very stably. With accidental coincidences subtracted, we obtained coincidence fringes with >90 % visibilities, and observed a violation of Bell's inequality by seven standard deviations. We also confirmed the preservation of the quantum correlation between the photons even after they had been separated by 20 km of optical fiber.
Entanglement distribution between distant parties is one of the most important and challenging tasks in quantum communication. Distribution of photonic entangled states using optical fiber links is a fundamental building block towards quantum networks. Among the different degrees of freedom, orbital angular momentum (OAM) is one of the most promising due to its natural capability to encode high dimensional quantum states. In this article, we experimentally demonstrate fiber distribution of hybrid polarization-vector vortex entangled photon pairs. To this end, we exploit a recently developed ai…
We demonstrate a fiber-based source of polarization-entangled photon pairs at visible wavelengths suitable for integration with local quantum processing schemes. The photons are created through birefringent phase-matching in spontaneous four-wave mixing inside a Sagnac interferometer. We address entanglement degradation due to temporal distinguishability of the photons to enable the generation of a spectrally unfiltered polarization-entangled photon-pair state with $95.86\pm0.10%$ fidelity to a maximally entangled Bell state, evaluated with a tomographic state reconstruction without applying a…
We present a full implementation of a quantum key distribution system using energy-time entangled photon pairs and functioning with a 30km standard telecom fiber quantum channel. Two bases of two orthogonal states are implemented and the setup is quite robust to environmental constraints such as temperature variation. Two different ways to manage chromatic dispersion in the quantum channel are discussed.
High-Sensitivity Fiber Interferometer for Gravitational Phase Shift Measurement on Entangled States
本文提出使用千米级光纤干涉仪测量路径纠缠光子的引力诱导相移，首次在无质量粒子上实验验证广义相对论与量子力学的结合。
We present an all fiber source of frequency entangled photon pairs by using four wave mixing in a Sagnac fiber loop. Special care is taken to suppress the impurity of the frequency entanglement by cooling the fiber and by matching the polarization modes of the photon pairs counter-propagating in the fiber loop. Coincidence detection of signal and idler photons, which are created in pair and in different spatial modes of the fiber loop, shows the quantum interference in the form of spatial beating, while the single counts of the individual signal (idler) photons keep constant. When the producti…
We present an experimental proposal for the generation of photon triplets based on third-order spontaneous para- metric downconversion in thin optical fibers. Our analysis includes expressions for the quantum state, which de- scribes the photon triplets and for the generation rate in terms of all experimental parameters. We also present, for a specific source design, numerically calculated generation rates.
Non-classical light sources based on a single quantum emitter are considered as core technology for multiple quantum network architectures. A large variety of sources has been developed, but the generated photons remained far from being utilized in established standard fiber networks. Here, we report a week-long transmission of polarization-entangled photons from a single InAs/GaAs quantum dot over a metropolitan network fiber. The emitted photons are in the telecommunication O-band, favored for fiber optical communication. We employ a polarization stabilization system overcoming changes of bi…
In this letter, we report a polarization-entangled photon-pair source based on type-II spontaneous parametric down conversion at telecom O-band in periodically poled silica fiber (PPSF). The photon-pair source exhibits more than 130 nm (~24 THz) emission bandwidth centered at 1306.6 nm. The broad emission spectrum results in a short biphoton correlation time and we experimentally demonstrate a Hong-Ou-Mandel interference dip with a full width of 26.6 fs at half maximum. Owing to the low birefringence of the PPSF, the biphotons generated from type-II SPDC are polarization-entangled over the ent…
Quantum measurements that use the entangled photons' polarization to encode quantum information require calibration and alignment of the measurement bases between spatially separate observers. Because of the changing birefringence in optical fibers arising from temperature fluctuations or external mechanical vibrations, the polarization state at the end of a fiber channel is unpredictable and time-varying. Polarization tracking and stabilization methods originally developed for classical optical communications cannot be applied to polarization-entangled photons, where the separately detected p…
Experimental Evaluation of Passive Polarization Compensation Techniques for Fiber-Distributed Polarization-Entangled Photons
该研究评估自由空间QHQ波片与光纤FPC两种被动偏振补偿技术，通过逐路径优化实现光纤偏振纠缠光子补偿，恢复高可见度、高保真度纠缠，为短距离量子通信链路提供系统框架。
We demonstrate non-degenerate down-conversion at 810 and 1550 nm for long-distance fiber based quantum communication using polarization entangled photon pairs. Measurements of the two-photon visibility, without dark count subtraction, have shown that the quantum correlations (raw visibility 89%) allow secure quantum cryptography after 100 km of non-zero dispersion shifted fiber using commercially available single photon detectors. In addition, quantum state tomography has revealed little degradation of state negativity, decreasing from 0.99 at the source to 0.93 after 100 km, indicating minima…
A Liquid-Core Fiber Platform for Classical and Entangled Two-Photon Absorption Measurements
本文提出一种甲苯填充液芯光纤平台，通过增强光与物质相互作用距离，实现低功率经典双光子吸收测量，并首次尝试波导中的纠缠双光子吸收测量，未观察到E2PA信号，设定了与近期报告一致的截面上限。
We theoretically demonstrate a method for producing the maximally path-entangled state (1/Sqrt[2]) (|N,0> + exp[iN phi] |0,N>) using intensity-symmetric multiport beamsplitters, single photon inputs, and either photon-counting postselection or conditional measurement. The use of postselection enables successful implementation with non-unit efficiency detectors. We also demonstrate how to make the same state more conveniently by replacing one of the single photon inputs by a coherent state.
Entanglement distribution over long distances is essential for many quantum communication schemes like quantum teleportation, some variants of quantum key distribution, or implementations of a quantum internet. Distributing entanglement through standard telecommunication fiber is particularly important for quantum key distribution protocols with low vulnerability over metropolitan distances. However, entanglement distribution over long distance through optical fiber so far could only be accomplished with moderate photon pair rates. In this work, we present entanglement distribution over 50km o…
We demonstrate a wavelength-tunable, fiber-coupled source of polarization-entangled photons with extremely high spectral brightness and quality of entanglement. Using a 25 mm PPKTP crystal inside a polarization Sagnac interferometer we detect a spectral brightness of 273000 pairs/(s mW nm), a factor of 28 better than comparable previous sources while state tomography showed the two-photon state to have a tangle of T=0.987. This improvement was achieved by use of a long crystal, careful selection of focusing parameters and single-mode fiber coupling. We demonstrate that, due to the particular g…
We present a fiber based source of polarization-entangled photon pairs that is well suited for quantum communication applications in the 1550nm band of standard fiber-optic telecommunications. Polarization entanglement is created by pumping a nonlinear-fiber Sagnac interferometer with two time-delayed orthogonally-polarized pump pulses and subsequently removing the time distinguishability by passing the parametrically scattered signal-idler photon pairs through a piece of birefringent fiber. Coincidence detection of the signal-idler photons yields biphoton interference with visibility greater …
Realizing long distance entanglement swapping with independent sources in the real-world condition is important for both future quantum network and fundamental study of quantum theory. Currently, demonstration over a few of tens kilometer underground optical fiber has been achieved. However, future applications demand entanglement swapping over longer distance with more complicated environment. We exploit two independent 1-GHz-clock sequential time-bin entangled photon-pair sources, develop several automatic stability controls, and successfully implement a field test of entanglement swapping o…
In this Letter, the generation of 1.5 μm discrete frequency entangled two-photon state is realized based on a piece of commercial polarization maintaining fiber (PMF). It is connected with a polarization beam splitter to realize a modified Sagnac fiber loop (MSFL). Correlated two-photon states are generated through spontaneous four wave-mixing process along the two propagation directions of the MSFL, and output from the MSFL with orthogonal polarizations. The quantum interference of them is realized through a 45° polarization collimation between polarization axes of PMFs inside and outside the…
Quantum-enhanced phase interrogation of a fiber-optic strain sensor
本研究展示了利用 N=2 NOON 态双光子纠缠态，通过光纤内马赫-曾德尔干涉仪读出，实现光纤应变传感器的量子增强相位 interrogation，使测量噪声低于标准量子极限，证明了光功率约束下的量子优势。
Distribution of Telecom Entangled Photons through a 7.7 km Antiresonant Hollow-Core Fiber
本研究首次通过7.7 km反谐振空芯光纤在1550 nm波段实现纠缠光子分发，验证其适用于长距离量子通信，且其低延迟、低色散特性可提升时间片量子密钥分发的安全密钥率。
The development and wide application of quantum technologies highly depend on the capacity of the communication channels distributing entanglement. Space-division multiplexing (SDM) enhanced channel capacities in classical telecommunication and bears the potential to transfer the idea to quantum communication using current infrastructure. Here, we demonstrate an SDM of polarization-entangled photons over a 411m long 19-core multicore fiber distributing polarization-entangled photon pairs through up to 12 channels simultaneously. The quality of the multiplexed transfer is evidenced by high pola…
Multi-color entangled states of light including low-loss optical fiber transmission and atomic resonance frequencies are essential resources for future quantum information network. We present the experimental achievement on the three-color entanglement generation at 852 nm, 1550 nm and 1440 nm wavelengths for optical continuous variables. The entanglement generation system consists of two cascaded non-degenerated optical parametric oscillators (NOPOs). The flexible selectivity of nonlinear crystals in the two NOPOs and the tunable property of NOPO provide large freedom for the frequency select…
Automated distribution of high-rate, high-fidelity polarization entangled photons using deployed metropolitan fibers
本研究针对真实光纤中纠缠光子脆弱、网络难以持续运行的问题，提出全自动偏振纠缠光子分发系统，在纽约34公里已部署光纤上实现近50万对/秒的速率、99%保真度及99.84%的15天持续运行 uptime，为实用化全天候纠缠网络奠定基础。
High-precision time transfer is of fundamental interest in physics and metrology. Quantum time transfer technologies that use frequency-entangled pulses and their coincidence detection have been proposed, offering potential enhancements in precision and better guarantees of security. In this paper, we describe a fiber-optic two-way quantum time transfer experiment. Using quantum nonlocal dispersion cancellation, time transfer over a 20-km fiber link achieves a time deviation of 922 fs over 5 s and 45 fs over 40960 s. The time transfer accuracy as a function of fiber lengths from 15 m to 20 km …
On-demand sources of entangled photons for the transmission of quantum information in the telecom C-band are required to realize fiber-based quantum networks. So far, non-deterministic sources of quantum states of light were used for long distance entanglement distribution in this lowest loss wavelength range. However, they are fundamentally limited in either efficiency or security due to their Poissonian emission statistics. Here, we show on-demand generation of entangled photon pairs in the telecom C-band by an InAs/GaAs semiconductor quantum dot. Using a robust phonon-assisted excitation sc…
Impact of polarization mode dispersion on entangled photon distribution
本研究建立了偏振模色散（PMD）与量子测量误差概率之间的综合模型，并通过实验验证，提出了减轻PMD对宽带纠缠光子影响的方法，为优化商业量子密钥分发系统提供了实验验证的框架。
We report experimental distribution of time-bin entangled qubits over 50 km of optical fibers. Using actively stabilized preparation and measurement devices we demonstrate violation of the CHSH Bell inequality by more than 15 standard deviations without removing the detector noise. In addition we report a proof of principle experiment of quantum key distribution over 50 km of optical fibers using entangled photon.
Successful implementation of several quantum information and communication protocols require distributing entangled pairs of quantum bits in reliable manner. While there exists a substantial amount of recent theoretical and experimental activities dealing with non-Markovian quantum dynamics, experimental application and verification of the usefulness of memory-effects for quantum information tasks is still missing. We combine these two aspects and show experimentally that a recently introduced concept of nonlocal memory effects allows to protect and distribute polarization entangled pairs of p…
Photon modes have an important role in characterizing the quantum sources of light. Proper coupling of various photon modes obtained in spontaneous parametric down conversion (SPDC) process in optical fibers is essential to generate an effective source of entangled photons. The two main pre-detection factors affecting the biphoton mode coupling in SPDC are the pump beam focusing parameter and the crystal thickness. We present the numerical and experimental results on the effect of pump focusing on conditional down-converted photon modes for a Type-I BBO crystal. We experimentally verify that b…
This paper reports the first demonstration of the generation and distribution of entangled photon pairs in the 1.5-um band using spontaneous four-wave mixing in a cooled fiber. Noise photons induced by spontaneous Raman scattering were suppressed by cooling a dispersion shifted fiber with liquid nitrogen, which resulted in a significant improvement in the visibility of two-photon interference. By using this scheme, time-bin entangled qubits were successfully distributed over 60 km of optical fiber with a visibility of 76%, which was obtained without removing accidental coincidences.
We demonstrate an optical-fiber based source of polarization entangled photon-pairs with improved quality and efficiency, which has been integrated with off-the-shelf telecom components and is, therefore, well suited for quantum communication applications in the 1550 nm telecom band. Polarization entanglement is produced by simultaneously pumping a loop of standard dispersion-shifted fiber with two orthogonally-polarized pump pulses, one propagating in the clockwise and the other in the counter-clockwise direction. We characterize this source by investigating two-photon interference between th…
High-brightness fiber-based Sagnac source of entangled photon pairs for multiplexed quantum networks
基于非线性萨格纳克干涉仪的高亮度光纤源产生纠缠光子对，支持极化和能量-时间纠缠，实现高归一化亮度和高纠缠质量，适用于多路复用量子网络。
Study of multiple degrees of freedom entanglement in optical fiber
针对光纤中携带轨道角动量的高维纠缠易退相干的问题，研究通过q板制备偏振-OAM混合纠缠态，利用偏振自由度调制OAM自由度，减缓传输中保真度下降，为提升光纤OAM态传输保真度提供理论指导。
Demonstration of a Monolithic and Fully Telecom-Fiber-Compatible Tunable Source of Polarization Entangled Photon Pairs Based on a van der Waals Material
利用3R-MoS₂薄膜的对称性，通过泵浦偏振调控产生两种贝尔态和共偏振光子对，实现光纤集成可调谐纠缠源，CAR达8.3×10³。
Proposal for the generation of photon pairs with nonzero orbital angular momentum in a ring fiber
本文提出利用热诱导χ^(2)非线性的石英环形光纤，通过自发参量下转换在准相位匹配条件下产生非零轨道角动量相关光子对。
We demonstrate the distribution of polarization-entangled photons for the purpose of quantum key distribution (QKD) along active telecom fibers. Entangled photon pairs of 810 nm wavelength generated by a Sagnac interferometer source were coupled into standard telecom single mode fibers. The fibers were either dark or carrying a standardized 1550 nm ethernet signals (1000BASE-ZX) with a nominal speed of 1 GBps from regular media converter devices, without any requirements on the optical power or spectrum transmitted. Our system demonstrates a QKD network covering 6 km in distance with a central…
Ultrabright fiber-coupled ploarization-entangled photon source with spectral brightness surpassing 2.0 MHz/mW/nm
本文提出一种超亮偏振纠缠光子源，通过优化单模光纤耦合与共线高斯模型，利用30-mm ppKTP晶体实现2.0 MHz/mW/nm的光谱亮度，保真度达97.8%，为卫星通信等高损耗长距离光链路提供实用方案。
We demonstrate the distribution of polarization entangled photons of wavelength 810 nm through standard telecom fibers. This technique allows quantum communication protocols to be performed over established fiber infrastructure, and makes use of the smaller and better performing setups available around 800 nm, as compared to those which use telecom wavelengths around 1550 nm. We examine the excitation and subsequent quenching of higher-order spatial modes in telecom fibers up to 6 km in length, and perform a distribution of high quality entanglement (visibility 95.6%). Finally, we demonstrate …
Highly Nondegenerate Entangled Photon Source for Fiber-Based Quantum Key Distribution
本研究提出一种高非退相干纠缠光子源，通过交叉晶体配置实现680nm和1550nm波长的光子对生成，为光纤量子密钥分发和长距离量子网络提供高效解决方案。
Entanglement distribution over metropolitan fiber using an on-chip broadband polarization entangled photon source
本文利用基于SOI平台的片上宽带硅纳米线双光子偏振纠缠源，在30公里城域光纤上实现了纠缠分发，并观测到CHSH不等式违反27.8个标准差，展示了硅光子技术在量子网络中的可扩展性。
We present a proof-of-principle experimental demonstration of a reconfigurable entanglement distribution scheme utilizing a poled fiber-based source of broadband polarization-entangled photon pairs and dense wavelength-division multiplexing. A large bandwidth (> 90 nm, centered at 1555 nm) and highly spectrally correlated nature of the entangled source can be exploited to allow for the generation of more than 25 frequency-conjugate entangled pairs when aligned to the standard 200 GHz ITU grid. In this work, three frequency-conjugate entangled pairs are used to demonstrate quantum key distribut…
We present a theoretical and experimental investigation of the emission characteristics and the flux of photon pairs generated by spontaneous parametric downconversion in quasi-phase matched bulk crystals for the use in quantum communication sources. We show that, by careful design, one can attain well defined modes close to the fundamental mode of optical fibers and obtain high coupling efficiencies also for bulk crystals, these being more easily aligned than crystal waveguides. We distinguish between singles coupling, conditional coincidence, and pair coupling, and show how each of these par…
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