Planar ion chip design for scalable quantum information processing

We investigate a planar ion chip design with a two-dimensional array of linear ion traps for scalable quantum information processing. Qubits are formed from the internal electronic states of trapped ^40Ca^＋ ions. The segmented electrodes reside in a single plane on a substrate and a grounded metal plate separately, a combination of appropriate rf and DC potentials is applied to them for stable ion confinement. Every two adjacent electrodes can generate a linear ion trap in and between the electrodes above the chip at a distance dependent on the geometrical scale and other considerations. The potential distributions are calculated by using a static electric field qualitatively. This architecture provides a conceptually simple avenue to achieving the microfabrication and large-scale quantum computation based on the arrays of trapped ions.

A grooved planar ion trap design for scalable quantum information processing

We describe a new electrode design for a grooved surface-electrode ion trap,which is fabricated in printed-circuitboard technology with segmented electrodes.This design allows a laser beam to get through the central groove to avoid optical access blocking and laser scattering from the ion trap surface.The confining potentials are modeled both analytically and numerically.We optimize the radio frequency（rf） electrodes and dc electrodes to achieve the maximum trap depth for a given ion height above the trap electrodes.We also compare our design with the reality ion chip MI I for practical considerations.Comparison results show that our design is superior to MI I.This ion trap design may form the basis for large scale quantum computers or parallel quadrupole mass spectrometers.

^(23)Na relaxometry: An overview of theory and applications

^(23)Na is a nuclear magnetic resonance(NMR)-active isotope with a nuclear spin quantum number of 3/2.^(23)Na relaxation phenomenon is at the core of ^(23)Na NMR measurement and analysis.Due to the dominance of quadrupolar interaction,the relaxation behavior of ^(23)Na is physically and mathematically more complex than that of a typical spin-1/2 isotope.In this review,we overview the semi-classical Redfield theory for deriving the formulations of ^(23)Na relaxation.We show that the relaxation behaviors of ^(23)Na can be quantitatively described by constructing the spectral density functions based on the second-order perturbation theory.In addition,we summarize the applications of ^(23)Na relaxometry in different research fields,including biomedicine,sodium ion batteries,and quantum information processing.Because sodium is an essential element in our body,food and industrial materials,the research on sodium by ^(23)Na NMR emerges as important future directions.The theoretical and practical understandings on ^(23)Na relaxation are the step stones for mastering advanced ^(23)Na NMR techniques.

Witnessing quantum phase transition in a non-Hermitian trapped ion system via quantum Fisher information

Quantum Fisher information is used to witness the quantum phase transition in a non-Hermitian trapped ion system with balanced gain and loss,from the viewpoint of quantum parameter estimation.We formulate a general non-unitary dynamic of any two-level non-Hermitian system in the form of state vector.The sudden change in the dynamics of quantum Fisher information occurs at an exceptional point characterizing quantum criticality.The dynamical behaviors of quantum Fisher information are classified into two different ways which depends on whether the system is located in symmetry unbroken or broken phase regimes.In the phase regime where parity and time reversal symmetry are unbroken,the oscillatory evolution of quantum Fisher information is presented,achieving better quantum measurement precision.In the broken phase regime,quantum Fisher information undergoes the monotonically decreasing behavior.The maximum value of quantum estimation precision is obtained at the exceptional point.It is found that the two distinct kinds of behaviors can be verified by quantum entropy and coherence.Utilizing quantum Fisher information to witness phase transition in the non-Hermitian system is emphasized.The results may have potential applications to non-Hermitian quantum information technology.

Determining spatial structures of ion crystals by simulated annealing method

Calculating the spatial structures of ion crystals is important in ion-trapped quantum computation. Here we demon- strate that the simulated annealing method is a powerful tool to evaluate the structures of ion crystals. By calculating equilibrium positions of 10 ions under harmonic potential and those of 120 ions under anharmonic potential, both with the standard procedure and simulated annealing method, we find that the standard procedure to evaluate spatial structures is complicated and may be inefficient in some cases, and that the simulated annealing method is more favorable.

One-step discrimination scheme on N-particle Greenberger-Horne-Zeilinger bases

We present an experimentally feasible one-step discrimination scheme on Bell bases with trapped ions, and then generalize it to the case of N-ion Greenberger-Horne-Zeilinger （GHZ） bases. In the scheme, all the orthogonal and complete N-ion GHZ internal states can be exactly discriminated only by one step, and thus it takes very short time. Moreover, the scheme is insensitive to thermal motion and dose not require the individual addressing of the ions. The Bell-state and GHZ-state one-step discrimination scheme can be widely used in quantum information processing based on ion-trap set-up.

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.

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。

Operational effects of the UNOT gate on classical and quantum correlations

The NOT gate that flips a classical bit is ubiquitous in classical information processing.However its quantum analogue,the universal NOT(UNOT) gate that flips a quantum spin in any alignment into its antipodal counterpart is strictly forbidden.Here we explore the connection between this discrepancy and how UNOT gates affect classical and quantum correlations.We show that while a UNOT gate always preserves classical correlations between two spins,it can non-locally increase or decrease their shared discord in ways that allow violation of the data processing inequality.We experimentally illustrate this using a multi-level trapped ^(171)Yb^+ ion that allows simulation of anti-unitary operations.

实现三比特量子控制相位门的离子阱方案(英文)

提出了一个利用离子阱系统实现三比特量子控制相位门的方案。在这个方案里,只需对囚禁离子辅以单比特旋转操作并与激光发生共振相互作用便可实现三比特控制相位门。相比其他文献中控制相位门的实现方案,此方案的优势在于所用的步骤更为简便易行。另外,此方案不需要任何测量。

Paul阱中共线两离子量子力学问题

运用熟知的级数截断方法,设计程序计算了线性Paul阱中两离子量子门系统Schrodinger方程的精确解,分析了质心波函数几个较低能级的态,并作出对应的几率分布图;计算相对距离的方均差△r2>h/2,相对运动的动量方均差△p2<h/2,并满足量子力学的Heiscnberg不确定度关系△r·△p>h/2,它满足压缩态的条件,即质心处于基态时,两离子相对位置的量子态是一个压缩态,并得到了两离子纠缠态的表达式。纠缠的存在对量子计算和量子信息有影响,量子测量的不确定度和纠缠是在实验中应加以考虑的问题。

多个囚禁离子纠缠态的制备

提出了一个制备任意多个囚禁离子叠加运动相干态的方案.制备的叠加运动相干态在位相空间呈一直线分布,该方案能用来制备任意多个囚禁离子的最大纠缠GHZ态.方案中仅使用了一束驻波光,驻波光的载波频率使得离子发生跃迁,而所有离子同时所处的位置可以不限于激光的波腹而处在任意位置.这能给实验带来许多便利,同时,只要选择激光的Rabi频率足够大,相应的操作时间可以足够短.

制备冷囚禁多离子W态的简单方案

提出实验上可行的制备冷囚禁多离子W态的方案。在此方案中制备的是对称W态,只需两个步骤,而在文献[Hàaner H,Hàansel W,Roos C F,et al.Nature,2005,438:643-646.]中制备相同的W态,则需要更多的操作步骤,考虑到消相干机制,减少纠缠态制备过程中的步骤是非常有必要的,并且在方案中只需要一束激光。

量子芯片的研究现状与应用

随着集成电路工艺的发展,摩尔定律逐渐走向终结,于是科学家们转向量子芯片的研究。目前最有前途的量子芯片分别是超导体系、半导体体系和离子阱体系。超导量子芯片电路设计难度随着比特数增多而增大,目前已实现20个超导量子比特的量子芯片。离子阱量子计算性能优异,但体积庞大,目前IonQ公司已实现13个171Yb+离子组成的离子阱系统11位全连接可编程量子计算机。半导体量子芯片的计算性能不如这两种,但是由于传统半导体工艺现在已基本成熟,只要在实验室里能够实现样品芯片,理论上讲大规模工业生产就不存在问题。目前科学家们认为未来将很快实现10个量子比特的纠缠。量子芯片的研究将带来计算速度的提升、量子通信安全性的实现等优势。文章简要介绍了近年来量子芯片的研究进展以及对未来应用的展望。

驻波场中囚禁离子的Wigner-Yanase偏态信息

研究了驻波场中囚禁离子的Wigner-Yanase偏态信息并得到了其恢复周期,发现此周期与离子布居数反转的恢复时间相同。对解析解与数值模拟进行分析,发现Wigner-Yanase偏态信息的恢复时间随Lamb-Dicke参数的增大而减小,随离子平均振动声子数的增大而增大;当离子质心从驻波场波节移向波腹时,Wigner-Yanase偏态信息的恢复时间变长。从理论上证明了囚禁离子振动态处于相干态时离子初始偏态信息恒为1/2,分析了离子与驻波激光场之间的量子纠缠特性。

Optimization of parameters of a surface-electrode ion trap and experimental study of influences of surface on ion lifetime

In this paper we report the optimal design and fabrication of a gold-on-silica linear segmented surface-electrode ion trap. By optimizing the thickness and width of the electrodes, we improved the trapping ability and trap scalability. By using some practical experimental operation methods, we successfully minimized the trap heating rate. Consequently, we could trap a string of up to 38 ions, and a zigzag structure with 24 ions, and transport two trapped ions to different zones. We also studied the influences of the ion chip surface on the ion lifetime. The excellent trapping ability and flexibility of operation of the planar ion trap shows that it has high feasibility for application in the development a practical quantum information processor or quantum simulator.

A cloud of laser cooled ^(40)Ca^+ in a linear ion trap

A cloud of 40Ca+is successfully trapped and cooled using the radiation of a red-detuned 397 nm laser beam and a resonant 866 nm laser beam in our prototype linear ion trap,which was designed and constructed for studying quantum information processing.We have characterized the size of the ion cloud,estimating the temperature to be in the order of milli-Kelvins.

可扩展的用于量子信息处理的刻槽平面离子芯片设计

研究设计了一个有效的可扩展的二维刻槽离子芯片。为了减少激光在离子芯片表面的散射,使被囚禁离子更加稳定,并使激光容易控制和探测成行的被囚禁离子,在每两个平行的射频电极中间刻槽使冷却光和探测光路径可穿过芯片。把控制离子运动的直流电极跟射频电极分开,减轻了不同电压对被囚禁离子的干扰,改进了对离子的控制。用有限元分析的方法对芯片表面上方的电势分布做了计算模拟。模拟结果表明,在这种新型的刻槽可扩展芯片上可以生成一个可扩展的离子阱阵列。这种结构提供了一个新颖的刻槽二维平面离子芯片,被囚禁其上的线形离子阵列可用来进行大型的量子信息处理。

囚禁离子非线性Jaynes-Cummings模型量子场熵演化特性

利用VonNeuuman量子约化熵理论研究了驻波激光场与囚禁在谐振势中的离子单量子共振相互作用系统中量子场熵的时间演化特性,通过数值计算详细讨论了Lamb-Dick参数、离子质心在驻波激光场中的位置以及囚禁离子初始状态对量子场熵演化特性的影响.结果表明:Lamb-Dick参数影响囚禁离子与驻波激光场之间量子纠缠的频率和幅度,其值越大离子与光场之间的平均纠缠程度越低;随着离子质心从驻波激光场的波节向波腹移动,二者之间量子纠缠的振荡频率逐渐变慢,纠缠强度逐渐减弱;随着囚禁离子处于激发态概率的减小,离子与光场之间的量子纠缠呈现先增强后减弱的变化趋势.这些特性对于纠缠态的制备以及利用囚禁离子进行量子通讯等信息处理过程有一定的参考价值.

平面刻槽离子阱的热噪声引起的离子加热研究

研究了和平面刻槽离子阱中的电压热涨落噪声引起的离子加热和离子加热的直接计算模型,给出了离子加热的加热尺度,并利用有限元分析方法计算了当刻槽宽度和射频电极宽度比例α发生变化时加热尺度的变化。同时,还利用涨落耗散原理计算了控制电极的阻抗热涨落对离子产生的加热效应,并给出了x和y方向电场涨落的谱密度表达式,通过计算给出了较好的α值。