A Test of Quantum Electrodynamics at High Fields

高场量子电动力学测试

• 批准号: EP/D068509/1
• 负责人: Richard Thompson
• 金额: $ 64.63万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FD068509%2F1
• 关键词: Test; Quantum; Electrodynamics; Fields

Quantum electrodynamics (QED) was the first quantum field theory to be formulated providing a radically new description of the electromagnetic force. So far it has successfully passed every experimental test at low and intermediate fields. A well-known example of QED effects at low fields, of the order of 10^9 V/cm, is the Lamb shift in hydrogen. At such low fields, the QED effects can still be treated perturbatively, only taking into account low order terms. However, up to now QED has never been tested at very much higher fields than this because of the practical difficulties of producing such fields in the laboratory. At high fields, perturbative QED is no longer valid, and higher order terms need to be evaluated carefully. Experiments carried out at high fields therefore test different aspects of QED and are complementary to high precision tests of the low order terms. Since quantum field theories are the cornerstone of modern physics testing these theories in the non-perturbative limit is extremely important. Heavy atoms that have been stripped of almost all their electrons are ideal 'laboratories' for tests of QED at high fields. These ions have electric field strengths of the order of 10^15 V/cm close to the nucleus. Such highly charged ions (HCI) can now be produced at the experimental storage ring (ESR) at GSI in Darmstadt, Germany. In the HITRAP facility being built at GSI, these ions will be slowed, trapped and cooled down to sub-eV energies, and made available to a wide variety of experiments. Our group has been involved in the planning stages of this facility and it has been our responsibility to design the laser spectroscopy experiments to test QED at high fields. The early stages of this work have been funded through a European Union FP5 collaboration (also called HITRAP). Now that the completion of the facility is in sight the various groups involved must seek funding at the national level to complete the project. Hydrogen-like (one electron) and lithium-like (three electrons) highly charged ions in particular are excellent examples of systems that allow for accurate studies of QED effects at high fields. The ground state hyperfine splitting (HFS) in these species probes the validity of QED at the extremely high fields found very close to the nucleus. Due to their simple electronic structure, accurate QED calculations can be performed for these systems, which could be compared for the first time with the accurate experimental results we wish to obtain. The only proposed method of disentangling the QED effects from nuclear effects, such as the Bohr-Weisskopf (BW) effect, is by measuring the ground state HFS in both H-like and Li-like ions. From the difference between these two HFS the BW effect can effectively be eliminated. This allows for a determination of the QED effects with an accuracy of the order of a few percent. In neutral atoms hyperfine transitions are weak transitions in the microwave region of the spectrum. In (HCI) the electric fields involved push these transitions into the visible region of the spectrum and increase their transition rates. H- and Li-like bismuth ions are of interest because the wavelengths corresponding to these hyperfine transitions are both accessible with standard lasers. A common experimental obstacle in previous measurements made in a storage ring was the Doppler width and shift of the transition due to the relativistic velocities of the ions. Other measurements performed in an EBIT (electron beam ion trap) are not as severely subject to this effect, but suffer from a low signal-to-background ratio. We propose to trap highly charged ions in a Penning trap, cool and compress the ions into a small cloud, and measure ground state hyperfine splittings by means of laser spectroscopy, with an accuracy of the order of 10-7. Preparatory work will be performed at Imperial College but the final experiments will be performed at the HITRAP facility in Germany.

量子电动力学（QED）是第一个要配制的量子场理论，提供了对电磁力的根本新描述。到目前为止，它已经成功地通过了低和中间领域的每个实验测试。低场处QED效应的一个众所周知的例子是10^9 v/cm的订单，是氢气中的羔羊移位。在这样的低场上，仅考虑低订单条款，仍可以扰动地处理QED效应。但是，到目前为止，由于在实验室中生产此类领域的实际困难，QED从未在非常高的领域进行测试。在高场上，扰动QED不再有效，需要仔细评估高阶项。因此，在高场上进行的实验测试了QED的不同方面，并与低阶项的高精度测试互补。由于量子场理论是现代物理学测试的基石，在非扰动极限中这些理论非常重要。被剥离的重量原子几乎所有电子都是理想的“实验室”，用于在高场上测试QED。这些离子的电场强度为10^15 v/cm，接近核。现在可以在德国达姆施塔特GSI的实验存储环（ESR）上生产这种高电荷离子（HCI）。在GSI建造的HITRAP设施中，这些离子将被放慢，捕获和冷却至子-EV能量，并可以用于各种实验。我们的小组参与了该设施的计划阶段，我们的责任是设计激光光谱实验以在高领域进行测试QED。这项工作的早期阶段是通过欧盟FP5合作（也称为HITRAP）资助的。既然该设施的完成即将到来，那么所涉及的各个团体必须在国家一级寻求资金才能完成该项目。特别是高电荷离子的氢气（一个电子）和锂样离子（三个电子）是系统的出色示例，可以准确研究高场QED效应。这些物种中的基态超精细分裂（HFS）探测了非常高的田地上QED的有效性，发现非常接近核。由于其简单的电子结构，可以为这些系统执行准确的QED计算，这可以首次与我们希望获得的准确实验结果进行比较。唯一提出的将QED效应与核效应（例如BOHR-WEISSKOPF（BW）效应）的方法是通过测量类似H样和Li样离子的基态HFS。从这两个HF之间的差异可以有效地消除BW效应。这允许确定QED效应的准确性数百分之几。在中性原子中，超精细转变是光谱微波区域中的弱转变。在（HCI）中，电场涉及将这些过渡推向光谱的可见区域并提高其过渡速率。 H-和Li样的二晶型离子引起了人们的关注，因为与这些超精细转变相对应的波长都可以使用标准激光器访问。存储环先前测量中的一个常见实验障碍物是由于离子的相对论速度而导致的多普勒宽度和转变的变化。在EBIT（电子束离子陷阱）中执行的其他测量值不那么严重受到此效果的影响，而是具有低信噪比的比率。我们建议将高电荷离子捕获在板条陷阱中，冷却和压缩离子成小云，并通过激光光谱法测量基态超细胞分裂，准确的阶数值为10-7。准备工作将在帝国大学进行，但最终的实验将在德国的Hitrap设施进行。

项目成果

Laser cooling of externally produced Mg ions in a Penning trap for sympathetic cooling of highly charged ions

• DOI: 10.1103/physreva.87.033423
• 发表时间: 2012-11
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Z. Andelkovic;R. Cazan;W. Nortershauser;S. Bharadia;D. Segal;R. Thompson;R. Johren;J. Vollbrecht;V. Hannen;M. Vogel

Population dynamics in sideband cooling of trapped ions outside the Lamb-Dicke regime

• DOI: 10.1103/physreva.99.013423
• 发表时间: 2018-09
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: M. Joshi;P. Hrmo;V. Jarlaud;F. Oehl;R. Thompson

Optical sideband spectroscopy of a single ion in a Penning trap

• DOI: 10.1103/physreva.89.032502
• 发表时间: 2014-03-06
• 期刊: PHYSICAL REVIEW A
• 影响因子: 2.9
• 作者: Mavadia, S.;Stutter, G.;Segal, D. M.
• 通讯作者: Segal, D. M.

Rapid crystallization of externally produced ions in a Penning trap

外部产生的离子在潘宁阱中快速结晶

• DOI: 10.1103/physreva.94.043410
• 发表时间: 2016
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Murböck T

Dynamics of laser-cooled Ca+ ions in a Penning trap with a rotating wall

• DOI: 10.1007/s00340-012-4871-6
• 发表时间: 2012-06-01
• 期刊: APPLIED PHYSICS B-LASERS AND OPTICS
• 影响因子: 2.1
• 作者: Bharadia, S.;Vogel, M.;Thompson, R. C.
• 通讯作者: Thompson, R. C.