Measuring small longitudinal phase shifts via weak measurement amplification

Weak measurement amplification,which is considered as a very promising scheme in precision measurement,has been applied to various small physical quantities estimations.Since many physical quantities can be converted into phase signals,it is interesting and important to consider measuring small longitudinal phase shifts by using weak measurement.Here,we propose and experimentally demonstrate a novel weak measurement amplification-based small longitudinal phase estimation,which is suitable for polarization interferometry.We realize one order of magnitude amplification measurement of a small phase signal directly introduced by a liquid crystal variable retarder and show that it is robust to the imperfection of interference.Besides,we analyze the effect of magnification error which is never considered in the previous works,and find the constraint on the magnification.Our results may find important applications in high-precision measurements,e.g.,gravitational wave detection.

用于高效高速量子网络节点的光纤腔-离子阱耦合系统的设计

本文的主要目的是设计新型的离子阱与光纤腔的耦合系统,此方案是通过制造一个在侧面和端面具有金属层的光纤腔实现。带有金属层的光纤腔可以传输光和电荷,同时,光纤端面的金属层可以屏蔽介质高反膜上的电荷。此系统旨在捕获单个^(138)Ba^(+)离子,并实现光纤腔与^(138)Ba^(+)离子493 nm荧光的耦合。为了有效地收集荧光光子,我们对整个系统进行理论分析,以实现各个部分的最佳耦合。光纤的腔长被设计为250μm,优化后的耦合参数为(g,κ,γ)/2π=(55,105,20)MHz。我们还通过分析振动、离子阱性能和热稳定性来提高系统的稳定性和可靠性。系统的核心部分是由热膨胀系数相近的材料构成,以提高热稳定性。系统还使用弹簧连接真空腔体,用于隔绝腔体内外的振动。我们从理论上分析制造该耦合系统的难点,并实验验证了部分关键技术。整个系统有望被扩展成一个复杂的量子网络,以实现量子计算和量子通信。

量子互文在中国科大的二十个春秋

量子互文性是量子力学最为奇妙和令人困惑的特征之一,它指的是量子力学中一个算符的测量结果取决于测量时实际被观测的所有算符的选择。中国科学技术大学在量子互文方向的研究具有悠久的历史。本文回顾了过去20年来中国科大在量子互文方向所取得的理论和实验进展。我们首先介绍著名的最简单的态无关量子互文性证明;而后展示几个基于光子系统的量子互文性实验测试;最后,我们讨论了量子互文性在广泛的量子信息科学中的作用及其在量子计算中的应用。

Bayesian Optimization for Wavefront Sensing and Error Correction

Algorithms for wavefront sensing and error correction from intensity attract great concern in many fields.Here we propose Bayesian optimization to retrieve phase and demonstrate its performance in simulation and experiment.For small aberration,this method demonstrates a convergence process with high accuracy of phase sensing,which is also verified experimentally.For large aberration,Bayesian optimization is shown to be insensitive to the initial phase while maintaining high accuracy.The approach’s merits of high accuracy and robustness make it promising in being applied in optical systems with static aberration such as AMO experiments,optical testing shops,and electron or optical microscopes.

Generation of visible Raman operation laser by a fiber electro-optical modulator feedback loop

Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence.Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise,which limits their performance in practical applications.In this work,we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator(VCO)to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain,where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop(PLL).The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches-80 d Bc/Hz@5 k Hz with a 20 k Hz loop bandwidth.Furthermore,this compact and robust scheme effectively reduces the system's complexity and cost,which is promising for extensive application in atomic,molecular,and optical physics.

Demonstration of controlled high-dimensional quantum teleportation

Controlled quantum teleportation(CQT), which is regarded as the prelude and backbone for a genuine quantum internet, reveals the cooperation, supervision, and control relationship among the sender, receiver, and controller in the quantum network within the simplest unit. Compared with low-dimensional counterparts, high-dimensional CQT can exhibit larger information transmission capacity and higher superiority of the controller's authority. In this article, we report a proof-of-principle experimental realization of three-dimensional(3D) CQT with a fidelity of 97.4% ± 0.2%. To reduce the complexity of the circuit, we simulate a standard 4-qutrit CQT protocol in a 9×9-dimensional two-photon system with high-quality operations. The corresponding control powers are 48.1% ± 0.2% for teleporting a qutrit and 52.8% ± 0.3% for teleporting a qubit in the experiment, which are both higher than the theoretical value of control power in 2-dimensional CQT protocol(33%). The results fully demonstrate the advantages of high-dimensional multi-partite entangled networks and provide new avenues for constructing complex quantum networks.

Simultaneous observation of quantum contextuality and quantum nonlocality

Quantum nonlocality and quantum contextuality are the most curious properties that change our understanding of nature, and were observed independently in recent decades. One important question is whether both properties can be observed simultaneously. In this paper, we show that in a qutrit-qutrit system we can observe quantum nonlocality and quantum contextuality at the same time. From the perspective of quantum information, our experiment proves in principle that the two resources, quantum nonlocality and quantum contextuality, can be utilized simultaneously.

Thermal expanded core ultraviolet fiber for optical cavity mode matching

We have demonstrated a mode matching method between two different fibers by a hybrid thermal expanded core technique, which can be applied to match the modes of fiber-based Fabry–Pérot cavities. Experimentally, this method has achieved an expansion of the ultraviolet fiber core by 3.5 times while keeping fundamental mode propagation. With the experiment parameters, the fundamental mode coupling efficiency between the fiber and micro-cavity can reach 95% for a plano-concave cavity with a length of 400 μm. This method can not only have potential in quantum photonics research but also can be applied in classical optical fields.

Experimentally realizing efficient quantum control with reinforcement learning

We experimentally investigate deep reinforcement learning(DRL)as an artificial intelligence approach to control a quantum system.We verify that DRL explores fast and robust digital quantum controls with operation time analytically hinted by shortcuts to adiabaticity.In particular,the protocol’s robustness against both over-rotations and off-resonance errors can still be achieved simultaneously without any priori input.For the thorough comparison,we choose the task as single-qubit flipping,in which various analytical methods are well-developed as the benchmark,ensuring their feasibility in the quantum system as well.Consequently,a gate operation is demonstrated on a trapped^(171) Yb^(+)ion,significantly outperforming analytical pulses in the gate time and energy cost with hybrid robustness,as well as the fidelity after repetitive operations under time-varying stochastic errors.Our experiments reveal a framework of computer-inspired quantum control,which can be extended to other complicated tasks without loss of generality.

Experimental demonstration of suppressing residual geometric dephasing

The geometric phase is regarded as a promising strategy in fault tolerance quantum information processing(QIP) domain due to its phase only depending on the geometry of the path executed. However, decoherence caused by environmental noise will destroy the geometric phase. Traditional dynamic decoupling sequences can eliminate dynamic dephasing but can not reduce residual geometric dephasing, which is still vital for high-precision quantum manipulation. In this work, we experimentally demonstrate effective suppression of residual geometric dephasing with modified dynamic decoupling schemes,using a single trapped171 Ybtion. The experimental results show that the modified schemes can reduce dephasing rate up to more than one order of magnitude compared with traditional dynamic decoupling schemes, where residual geometric dephasing dominates. Besides, we also investigate the impact of intensity and correlation time of the low-frequency noise on coherence of the quantum system. And we confirm these methods can be used in many cases.

Experimental realization of nonadiabatic holonomic single‐qubit quantum gates with two dark paths in a trapped ion

For circuit-based quantum computation,experimental implementation of a universal set of quantum logic gates with high-fidelity and strong robustness is essential and central.Quantum gates induced by geometric phases,which depend only on global properties of the evolution paths,have built-in noise-resilience features.Here,we propose and experimentally demonstrate nonadiabatic holonomic single-qubit quantum gates on two dark paths in a trapped ^(171)γδ^(+)ion based on four-level systems with resonant drives.We confirm the implementation with measured gate fidelity through both quantum process tomography and randomized benchmarking methods.Meanwhile,we find that nontrivial holonomic two-qubit quantum gates can also be realized within current experimental technologies.Compared with previous implementations,our experiments share both the advantages of fast nonadiabatic evolution and robustness against systematic errors.Therefore,our experiments confirm a promising method for fast and robust holonomic quantum computation.

Fast and wide-band tuning single-mode microlaser based on fiber Fabry-Perot microcavities

A narrow-linewidth laser operating at the telecommunications band combined with both fast and wide-band tuning features will have promising applications.Here we demonstrate a single-mode(both transverse and longi-tudinal mode)continuous microlaser around 1535 nm based on a fiber Fabry-Pirot microcavity,which achieves wide-band tuning without mode hopping to the 1.3 THz range and fast tuning rate to 60 kHz and yields a frequency scan rate of 1.6× 10^17Hz/s.Moreover,the linewidth of the laser is measured as narrow as3.l MHz.As the microlaser combines all these features into one fiber component,it can serve as the seed laser for versatile applications in optical communication,sensing,frequency-modulated continuous-wave radar,and high-resolution imaging.

Experimental observation of quantum nonlocality in general networks with different topologies

Nonlocal correlation plays an important role in device independent quantum information processing.The stan-dard Bell nonlocality has been well studied with single local hidden variables,however the nonlocal correlations in general networks with several independent quantum sources and distant observers have been far less explored.Here,by using three independent entangled photon sources and recently constructed nonlinear Bell inequalities,we experimentally test the nonlocal correlations in the network scenario with different topologies.The violation of the inequalities can be obtained simply with separate measurements,which is much more favourable from the practical point of view.Our experiment results show a violation as 0.7779±0.0093 for the star network,and 0.7303±0.0024 for the chain network.Furthermore,we demonstrate that more measurement settings for each observer can bound more information against an eavesdropper.

Experimental investigation of measurement incompatibility of mutually unbiased bases

Incompatible measurements are of fundamental importance to re-vealing the peculiar features of quantum theory,and are also use-ful resources in various quantum information tasks.In this work,we investigate the quantum incompatibility of mutually unbiased bases(MUBs)within the operational framework of quantum resource the-ory,and report an experimental validation via the task of state dis-crimination.In particular,we construct an experimentally friendly witness to detect incompatible MUBs,based on the probability of cor-rectly discriminating quantum states.Furthermore,we prove that the noise robustness of MUBs can be retrieved from violating the above witness.Finally,we experimentally test the incompatibility of MUBs of dimensionality ranging from 2 to 4,and demonstrate that it is more robust to noise,as either the dimensionality of measurements or the number of MUBs increases.Our results may aid the exploration of the essential roles of incompatible measurements in both theoretical and practical applications in quantum information.