Molecular Ion Entanglement Detection by Single-Molecule Fluorescence

通过从原子或分子中移除电子，人们创造了一个“手柄”，允许人们利用电场和/或磁场抓住它并抓住它。长期以来，人们一直认为，以这种方式捕获和操纵原子和分子的能力具有巨大的科学和技术潜力，其应用范围从量子控制的化学到物理学基本理论的精确测试，这些基本理论几乎构成了所有现代技术的基础。被捕获的原子(及其电离对应物)已经被许多小组研究过，但捕获和探测相对脆弱的分子更加困难(尽管潜在更有意义)。分子最大的未开发潜力与其旋转和振动的能力有关，这是原子所没有的内部自由度。然而，在实现被捕获分子的全部潜力之前，必须开发出在不破坏分子的过程中确定其旋转和振动程度的技术。在这里，被支持的研究小组建议以这样一种方式捕捉被捕获的分子的相机图像，即只有当它们具有明确定义的旋转和振动能量时，它们才出现在照片中。这些相机图像将提供一种非破坏性地确定被捕获分子的旋转和振动的方法，探测分辨率可以达到单分子水平。预计这些技术的发展最终将在化学工业和更先进的量子计算机的实现中得到应用。在之前NSF的支持下，西北大学得到支持的研究小组展示了一种技术，使用单个飞秒激光同时从所有热填充激发能级光学泵浦来控制捕获分子的量子旋转态。这项技术适用于具有特殊内部结构的分子离子，这些离子具有所谓的对角电子跃迁，允许许多光子在振动被激发之前被散射。这些分子可以粗略地认为是分子世界中的碱性原子。在目前的工作中，捕获的分子离子的荧光将直接在CCD相机上成像，从而照亮一维库仑晶体中的某些位置，在该位置上的单个分子离子处于被探测的量子态。因此，这些ccd图像将提供单分子分辨率的分子状态读数。然后，该小组将使用荧光态读数来观察共捕获的极性分子离子之间的电偶极介导的旋转纠缠。这项工作的未来扩展可能包括使用光学相移无散射检测单分子，直接使用重分子离子荧光读出进行宇称破坏和时间反转对称破坏搜索，实现条件量子门，分子离子与外部电路纠缠，以及研究离子陷阱中的退相干动力学。

By removing an electron from an atom or molecule, one creates a "handle" which allows one to grab it and hold onto it using electric and/or magnetic fields. The ability to trap and manipulate atoms and molecules in this way has long been recognized to hold great scientific and technological potential, with applications ranging from quantum-controlled chemistry to precision tests of the basic theories of physics which underlie virtually all of modern technology. Trapped atoms (and their ionized counterparts) have been studied by many groups, but it is more difficult (although potentially more rewarding) to trap and probe the relatively fragile molecules. The mostly untapped potential of molecules relates to their ability to rotate and vibrate, internal degrees of freedom which are absent in atoms. However, before the full potential of trapped molecules can be realized, techniques must be developed to determine their degree of rotation and vibration without destroying the molecules in the process. Here, the supported research group proposes capturing camera images of trapped molecules in such a way that they only appear in the picture if they have specific well-defined rotational and vibrational energies. These camera images will provide a means to non-destructively determine the rotation and vibration of trapped molecules, with detection resolution achievable down to the single-molecule level. It is anticipated that the development of these techniques will eventually find application in the chemical industry and in the realization of more advanced quantum computers.With prior NSF support, the supported research group at Northwestern University demonstrated a technique to control the quantum rotational state of trapped molecules using a single femtosecond laser to simultaneously optically pump from all thermally populated excited levels. This technique works for molecular ions with a special internal structure, those possessing a so-called diagonal electronic transition, allowing many photons to be scattered before vibrations are excited. These molecules can be roughly thought of as the alkali atoms of the molecule world. In the present work, fluorescence of trapped molecular ions will be imaged directly on a CCD camera, lighting up certain locations in a one-dimensional Coulomb crystal where the single molecular ion at that site is in the probed quantum state. These CCD images will thus provide molecular state readout with single-molecule resolution. The group will then use fluorescence state readout in order to observe electric-dipole mediated rotational entanglement between co-trapped polar molecular ions. Future extensions of the work proposed here could include scattering-free detection of single molecules using optical phase shifts, directly using heavy molecular ion fluorescence readout for parity-violation and time-reversal symmetry violation searches, implementations of conditional quantum gates, entangling molecular ions with external circuits, and studies of decoherence dynamics in ion traps.