Quantum Networking with Fibre-Coupled Ions

光纤耦合离子的量子网络

• 批准号: EP/J003670/1
• 负责人: Matthias Keller
• 金额: $ 63.45万
• 依托单位: University of Sussex
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FJ003670%2F1
• 关键词: Quantum; Networking; Fibre; Coupled; Ions

In the course of the project, we will develop a system to transfer quantum information between distant ions deterministically, using single photons in an optical fibre as carrier. This device will be a key building block of a so-called quantum network, which in the future will connect quantum computers like the internet does with present-day computers.Already today single quanta of light (photons) are used to transmit information securely over long distances, a process called quantum communication. The laws of quantum mechanics would foil any attempt of eavesdropping. Quantum effects can also be used to perform computations. Re-searchers use single ions stored in linear traps as quantum bits, replacing the classical bits in ordi-nary computers. These quantum bits are manipulated with laser light. In our project, we will com-bine the areas of quantum computation and quantum communication by building an efficient user-controlled interface (a quantum link) between ions and photons. The transfer of quantum states from ions to photons requires that we strongly couple the two sys-tems. We can achieve this by surrounding the ion with two mirrors, forming a cavity and enhancing the interaction of ions and photons. The conversion process from the ion-qubit to the photon-qubit will be steered with a suitable laser pulse applied to the ion. A photon will be generated with one of its properties (polarization) depending on the state of the ion. Particularly interesting are cases where the atom is in a superposition of two possible states, a situation that is allowed in quantum mechanics. Our interface will make sure that the quantum state of the photon is identical that of the ion and will therefore have a superposition of polarizations. Even more interesting are the cases when the ion doesn't transfer all information on its original su-perposition state to the photon, but retains some of it. The ion and the emitted photon will then be in a linked or entangled state, where the outcome of a measurement on the separate components is unpredictable, but combining the results of the two systems one always finds perfect correlation. Previously these states have been produced in a controlled way only in one location, while we will be able to distribute entanglement over long distances. This will be one of the major achievements of our project. We will also reverse this process and transfer the quantum state of an incoming photon to that of an ion in our cavity. Combining the two processes, we can transfer quantum states from one ion to a distant ion, or entangle their quantum states. This is done very efficiently, as nothing in the process is left to chance. This kind of entanglement is an important resource for performing efficient quantum computation in the future.To achieve our goals, we have to master two technologies: first we need to store a single ion in a very small region of space (less than 40 nm) for a long time (hours). This is possible with the help of a microscopic ion trap. The mirrors of the cavity surrounding the ion must have extremely high quality, allowing 200,000 reflections of the photon without loss. In addition, we must put the mirrors very close to the ion, to enhance the interaction between ion and photon. Combining the micro-scopic trap with a small mirror separation is the main experimental challenge of this project. By employing laser machined end facets of optical fibres as mirrors, we can achieve the ultimate miniaturization of the cavity. Furthermore, the cavity emission will be coupled directly into the fibre for reliable long distance transmission.

在项目过程中，我们将开发一种利用光纤中的单光子作为载体，在远距离离子之间确定性地传输量子信息的系统。这种设备将是所谓的量子网络的关键组成部分，在未来，量子网络将像互联网一样连接量子计算机和当今的计算机。现在已经使用单量子(光子)来安全地远距离传输信息，这一过程被称为量子通信。量子力学定律将挫败任何窃听企图。量子效应也可以用来进行计算。研究人员使用存储在线性陷阱中的单个离子作为量子比特，取代了常规计算机中的经典比特。这些量子比特是用激光操控的。在我们的项目中，我们将通过在离子和光子之间建立一个有效的用户控制接口(量子链路)来结合量子计算和量子通信领域。从离子到光子的量子态转换需要我们将这两个系统强耦合。我们可以通过用两面镜子包围离子，形成一个腔，并加强离子和光子的相互作用来实现这一点。从离子量子比特到光子量子比特的转换过程将由适当的激光脉冲施加到离子上来控制。根据离子的状态，会产生一个具有某种属性(偏振)的光子。特别有趣的是原子处于两种可能状态的叠加，这种情况在量子力学中是允许的。我们的界面将确保光子的量子态与离子的量子态相同，因此将有极化的叠加。更有趣的是，离子并没有将所有关于其原始叠加态的信息传递给光子，但保留了其中的一些信息。然后离子和发射的光子将处于链接或纠缠状态，在这种状态下，对单独分量的测量结果是不可预测的，但将两个系统的结果结合在一起，总能找到完美的关联。以前，这些态只在一个位置以受控的方式产生，而我们将能够在很长的距离内分布纠缠。这将是我们项目的主要成果之一。我们还将逆转这一过程，并将入射光子的量子态转换为腔中离子的量子态。结合这两个过程，我们可以将量子态从一个离子转移到另一个离子，或者将它们的量子态纠缠在一起。这是非常高效的，因为在这个过程中没有留下任何偶然的东西。这种纠缠是未来进行高效量子计算的重要资源。为了实现我们的目标，我们必须掌握两项技术：首先，我们需要在非常小的空间区域(小于40 nm)长时间(数小时)存储单个离子。在微型离子陷阱的帮助下，这是可能的。围绕离子的腔镜必须具有极高的质量，允许20万次光子无损失地反射。此外，我们必须把反射镜放在离离子很近的地方，以增强离子和光子之间的相互作用。将微观陷阱与小镜面分离相结合是该项目的主要实验挑战。通过使用激光加工的光纤端面作为反射镜，我们可以实现腔的最终小型化。此外，腔发射将直接耦合到光纤中，以实现可靠的长距离传输。

项目成果

Two-frequency operation of a Paul trap to optimise confinement of two species of ions

保罗陷阱的双频操作可优化两种离子的限制

• DOI: 10.1016/j.ijms.2018.05.007
• 发表时间: 2018
• 期刊: International Journal of Mass Spectrometry
• 影响因子: 1.8
• 作者: Foot C

An integrated fiber trap for single-ion photonics

• DOI: 10.1088/1367-2630/15/5/053011
• 发表时间: 2013-05-08
• 期刊: NEW JOURNAL OF PHYSICS
• 影响因子: 3.3
• 作者: Takahashi, Hiroki;Wilson, Alex;Lange, Wolfgang
• 通讯作者: Lange, Wolfgang

Precise positioning of an ion in an integrated Paul trap-cavity system using radiofrequency signals

• DOI: 10.1080/09500340.2017.1406158
• 发表时间: 2018-01-01
• 期刊: JOURNAL OF MODERN OPTICS
• 影响因子: 1.3
• 作者: Kassa, Ezra;Takahashi, Hiroki;Keller, Matthias
• 通讯作者: Keller, Matthias

Comparative Numerical Studies of Ion Traps with Integrated Optical Cavities

具有集成光学腔的离子阱的比较数值研究

• DOI: 10.1103/physrevapplied.6.044008
• 发表时间: 2016
• 期刊: Physical Review Applied
• 影响因子: 4.6
• 作者: Podoliak N

Harnessing the mode mixing in optical fiber-tip cavities

• DOI: 10.1088/1361-6455/aa640a
• 发表时间: 2017-04-28
• 期刊: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
• 影响因子: 1.6
• 作者: Podoliak, Nina;Takahashi, Hiroki;Horak, Peter
• 通讯作者: Horak, Peter