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。

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.

Wave propagation across fluid-solid interfaces with LBM-LSM coupling schemes

Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluid-solid interface. To address this challenge, we propose a novel numerical scheme that integrates the lattice Boltzmann method(LBM) and lattice spring model(LSM). In this scheme, LBM simulates viscoacoustic wave propagation in the fluid area and LSM simulates elastic wave propagation in the solid area. We also introduce three different LBM-LSM coupling strategies, a standard bounce back scheme, a specular reflection scheme, and a hybrid scheme, to describe wave propagation across fluid-solid boundaries. To demonstrate the accuracy of these LBM-LSM coupling schemes, we simulate wave propagation in a two-layer model containing a fluid-solid interface. We place excitation sources in the fluid layer and the solid layer respectively, to observe the wave phenomena when seismic waves propagate to interface from different sides. The simulated results by LBM-LSM are compared with the reference wavefields obtained by the finite difference method(FDM) and the analytical solution(ANA).Our LBM-LSM coupling scheme was verified effective, as the relative errors between the LBM-LSM solutions and reference solutions were within an acceptable range, sometimes around 1.00%. The coupled LBM-LSM scheme is further used to model seismic wavefields across a more realistic rugged seabed,which reveals the potential applications of the coupled LBM-LSM scheme in marine seismic imaging techniques, such as reverse-time migration and full-waveform inversion. The method also has potential applications in simulating wave propagation in complex two-and multi-phase media.

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.