A Quantum Gas of Ultracold Polar Molecules

超冷极性分子的量子气体

• 批准号: EP/H003363/1
• 负责人: Simon Cornish
• 金额: $ 138.96万
• 依托单位: Durham University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FH003363%2F1
• 关键词: Quantum; Gas; Ultracold; Polar; Molecules

The advent of laser cooling revolutionized atomic physics and precipitated the realization of quantum degenerate gases in which the quantum mechanical nature of the particles dominates over their classical behaviour. These dilute atomic gases, in the form of Bose-Einstein condensates (BEC) and Fermi-degenerate gases, have proved surprisingly rich and are now routinely studied throughout the world. More recently, the quest for the creation of ultracold and quantum degenerate molecular samples has become of paramount interest to both the atomic and molecular physics and physical chemistry communities. The rich internal structure of molecules coupled with the remarkable control afforded by ultracold systems offers enormous scope for applications in fields ranging from precision measurement and high-resolution spectroscopy to ultracold chemistry and quantum information processing. Perhaps most intriguing of all is the possibility to produce ultracold quantum gases of heteronuclear molecules where the long-range, anisotropic dipole-dipole interaction is predicted to give rise to a rich spectrum of novel quantum phases.The laser cooling techniques at the heart of the spectacular experimental advances in atomic physics do not, however, work for molecules due to their complex internal rotational and vibrational structure. This has prompted a host of alternative approaches to create ultracold molecular gases to be developed which all rely on cooling pre-existing molecules from room temperature. This proposal, however, follows an alternative scheme which exploits the huge advances in laser cooling and trapping of atomic gases by carefully assembling ultracold molecules from ultracold atoms. Starting from an ultracold mixed species quantum gas of Rb and Cs, the objective is to create ultracold RbCs molecules in the rovibrational ground state following a two-step conversion process.The first step relies upon the existence of scattering resonances in the collisions between ultracold atoms that result from a coupling between the free atoms and a quasibound molecular state known as a Feshbach resonance. The simple application of an appropriate magnetic field ramp in the vicinity of a Feshbach resonance results in the highly efficient conversion of atoms to molecules whilst preserving the phase-space density of the original atomic sample. However, such Feshbach molecules are extremely fragile; existing in very weakly bound states close to the dissociation threshold they are generally unstable when colliding with each other. The challenge of the second step is to transfer these molecules to the collisionally stable ground state without heating the sample. This can be achieved using a process known as stimulated Raman adiabatic passage (STIRAP) in which two laser fields are applied to the molecule connecting the initial weakly bound state to the ground state via a third excited state. Remarkably, with the appropriate time-dependent laser pulses, the STIRAP process permits the coherent transfer of the molecules to the ground state without populating the excited state thereby removing the possibility of loss due to spontaneous decay. The overall conversion process can be highly efficient with negligible heating so that the temperature and density of the resulting molecular quantum gas mirror the initial parameters of the atomic mixture.In the case of RbCs, it is predicted that rovibrational ground state molecules can be produced using a single STIRAP stage, creating a stable bosonic molecular dipolar quantum gas which could be trapped and further cooled to quantum degeneracy. To achieve this ambitious objective we propose to combine state-of-the-art experiments in synergy with world leading theoretical support into a transformative program of research that stands to cement the UK's position at the forefront of an exciting international field.

激光冷却的出现彻底改变了原子物理学，并促成了量子简并气体的实现，在这种气体中，粒子的量子力学性质决定了它们的经典行为。这些稀薄的原子气体，以玻色-爱因斯坦凝聚态(BEC)和费米简并气体的形式被证明是出人意料的丰富，现在全世界都在进行例行的研究。最近，对创造超冷和量子简并分子样品的探索已经成为原子、分子物理和物理化学界的最大兴趣。分子丰富的内部结构，再加上超冷系统所提供的卓越控制，为从精密测量和高分辨率光谱到超冷化学和量子信息处理等领域提供了巨大的应用空间。也许最耐人寻味的是产生异核分子的超冷量子气体的可能性，在这种情况下，长距离、各向异性的偶极-偶极相互作用被预测会产生丰富的新量子相。然而，作为原子物理学壮观实验进展的核心的激光冷却技术，由于分子复杂的内部旋转和振动结构，并不适用于分子。这促使了许多创造超冷分子气体的替代方法被开发出来，这些方法都依赖于从室温冷却预先存在的分子。然而，这一提议遵循了另一种方案，该方案利用了激光冷却和捕获原子气体方面的巨大进步，通过仔细地从超冷原子中组装超冷分子。从Rb和Cs的超冷混合量子气体出发，目标是经过两步转换过程，在振动基态下产生超冷RbCs分子。第一步依赖于超冷原子之间碰撞散射共振的存在，这是自由原子与被称为Feshbach共振的准束缚分子态耦合的结果。在Feshbach共振附近简单地应用适当的磁场斜坡，可以在保持原始原子样品的相空间密度的同时，高效地将原子转化为分子。然而，这样的Feshbach分子是极其脆弱的；它们存在于接近解离阈值的非常弱的束缚状态，当它们相互碰撞时通常是不稳定的。第二步的挑战是在不加热样品的情况下将这些分子转移到碰撞稳定的基态。这可以使用被称为受激拉曼绝热通道(STIRAP)的过程来实现，在该过程中，将两个激光场施加到通过第三激发态连接初始弱束缚态和基态的分子。值得注意的是，在适当的含时激光脉冲下，STIRAP过程允许分子在不填充激发态的情况下相干转移到基态，从而消除了自发衰变造成损失的可能性。整个转换过程效率很高，可以忽略加热，从而得到的分子量子气体的温度和密度反映了原子混合物的初始参数。在RBCs的情况下，预测可以使用单个STIRAP级来产生旋转基态分子，从而产生稳定的玻色子分子偶极量子气体，它可以被捕获并进一步冷却到量子简并。为了实现这一雄心勃勃的目标，我们建议将最先进的协同实验与世界领先的理论支持结合起来，形成一个变革性的研究计划，以巩固英国在一个令人兴奋的国际领域的前沿地位。

项目成果

Hyperfine structure of 2 S molecules containing alkaline-earth-metal atoms

含碱土金属原子的2S分子的超精细结构

• DOI: 10.1103/physreva.97.042505
• 发表时间: 2018
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: Aldegunde J

A high phase-space density mixture of 87Rb and 133Cs: towards ultracold heteronuclear molecules

87Rb 和 133Cs 的高相空间密度混合物：面向超冷异核分子

• DOI: 10.1140/epjd/e2011-10716-1
• 发表时间: 2011
• 期刊: The European Physical Journal D
• 作者: Cho H

Hyperfine structure of alkali-metal diatomic molecules

• DOI: 10.1103/physreva.96.042506
• 发表时间: 2017-10-27
• 期刊: PHYSICAL REVIEW A
• 影响因子: 2.9
• 作者: Aldegunde, Jesus;Hutson, Jeremy M.
• 通讯作者: Hutson, Jeremy M.

Ultracold molecules for quantum simulation: rotational coherences in CaF and RbCs

• DOI: 10.1088/2058-9565/aaee35
• 发表时间: 2019-01-01
• 期刊: QUANTUM SCIENCE AND TECHNOLOGY
• 影响因子: 6.7
• 作者: Blackmore, Jacob A.;Caldwell, Luke;Cornish, Simon L.
• 通讯作者: Cornish, Simon L.

Feshbach resonances, weakly bound molecular states, and coupled-channel potentials for cesium at high magnetic fields

• DOI: 10.1103/physreva.87.032517
• 发表时间: 2012-12
• 期刊: Physical Review A
• 影响因子: 2.9
• 作者: M. Berninger;A. Zenesini;Bo Huang;Walter Harm;H. Nagerl;F. Ferlaino;R. Grimm;P. Julienne;J. Hutson