Engineering a new generation of atom interferometers

在量子系统操纵方面取得的巨大进展为现实的量子技术的产生开辟了新的途径。值得注意的是，量子力学的许多违反直觉的表现正在成为下一代设备的关键特征，其性能将击败经典机器。原子干涉测量就是一个典型的例子。根据量子力学，粒子可以表现得像波一样，像光一样表现出干涉。此外，它们对周围环境非常敏感，并且它们具有质量，这使得它们成为测量线性加速度和旋转的非常强大的传感器。然而，在实际应用中实现可靠的原子干涉仪仍然具有挑战性。最先进的设备是基于原子样品，这些原子样品在真空装置内由于重力而下落时被操纵。这些干涉仪目前正在达到其极限性能，但受到技术问题的限制。它们的最终灵敏度又取决于可用于询问的时间和有限的原子数。提高灵敏度的直接解决方案在于以装置的尺寸为代价来扩大询问区域，并且以原子探针的空间分辨率为代价来增加原子数目。为了获得高灵敏度，同时保持设备紧凑，新一代的干涉仪的基础上被困和引导原子正在出现。这些设备有几个优点：原子不下降，询问时间可以很长，使用BEC保证微观空间分辨率，原子间的相互作用允许制备纠缠态，超过有限原子数设定的标准量子极限。新的挑战也出现了：限制势和原子间相互作用的影响必须控制在一个可接受的水平。该项目旨在实现新型的基于BEC的量子传感器，通过结合超冷原子领域（及其他领域）目前最强大的操纵技术，该传感器将能够超越电流捕获和引导干涉仪的局限性。两个关键要素是通过空间光调制器精确定制光学势和控制相互作用。这种特殊的实验控制将得到理论优化，如捷径绝热和最佳控制技术的帮助。在现有的原子干涉仪中，分束器是通过两束布拉格或拉曼激光脉冲实现的。相反，我们将设计创新的分离器，直接集成到限制原子的光波导中。它们可以连续工作，不需要额外的激光束。干涉仪的所有元件（分束器、相位累积器和复合器）将通过适当地雕刻一个单个激光束而集成到同一设备中。首先，一个完整的马赫-曾德尔操作将与可调相互作用的凝聚体进行。相互作用的可忽略或弱吸引值将用于抑制相互作用引起的退相干或创建无色散波包。因此，对于这样的干涉仪期望高灵敏度。在该项目的第二阶段，我们将展示一个类似萨尼亚克的干涉仪与非相互作用的凝聚在一个封闭的电路传播。这将实现制导原子陀螺仪，其实现一直是一个长期的目标，并在惯性导航中找到重要的应用。最后，我们将制作介观光镊，以实现马赫-曾德尔干涉术的动态双井势。通过将镊子分开，我们将控制两个威尔斯阱之间的耦合，通过设置强排斥相互作用，我们将产生最佳的自旋压缩态。

The huge progress achieved in the manipulation of quantum systems is opening novel routes towards the generation of realistic quantum-based technology. Notably many counterintuitive manifestations of quantum mechanics are turning to be key features for next generation devices, whose performances will beat those of classical machines. Atom interferometry is a hallmark example of that. According to quantum mechanics particles can behave like waves, showing interference as well as light does. In addition, they are very sensitive to the surrounding environment and they have mass, which make of them extremely powerful sensors for measuring linear accelerations and rotations. Implementing reliable atom interferometers for practical applications is however still challenging. State-of-the-art devices are based on atomic samples which are manipulated while they fall due to gravity inside a vacuum apparatus. These interferometers are currently reaching their ultimate performances being limited by technical issues. Their ultimate sensitivity depends in turn on the time available for the interrogation and on the finite atom number. An immediate solution to improve the sensitivity consists in enlarging the interrogation area, at the expenses of the size of the device, and increasing the atom number, at the expenses of the spatial resolution of the atomic probe. To obtain high sensitivity while maintaining the devices compact, a new generation of interferometers based on trapped and guided atoms is emerging. These devices have several advantages: the atoms do not fall and the interrogation time can be long, the use of BECs guarantees micrometrical spatial resolution, and interatomic interactions allow for the preparation of entangled states surpassing the standard quantum limit set by the finite atom number. New challenges also arise: the effects of the confining potentials and interatomic interactions must be controlled at a metrological level. The proposed project aims at realizing novel BEC-based quantum sensors which will be able to surpass the limitations of current trapped and guided interferometers by combining some of the most powerful manipulation techniques currently available in the field of ultracold atoms (and beyond). The two key elements are the accurate tailoring of the optical potentials by a spatial light modulator, and the control of the interactions. This exceptional experimental control will be assisted by theoretical optimization such as short-cut-to-adiabaticity and optimal control techniques. In most atom interferometers to date, the beam splitters are realized by pulsing two laser beams in Bragg or Raman configuration. We will instead engineer innovative splitters directly integrated into the optical waveguides which confine the atoms. They can operate continuously and without the need of extra laser beams. All the elements of the interferometer (beam splitter, phase accumulation and recombiner) will be integrated into the same device by properly sculpturing one single laser beam. First, a complete Mach-Zehnder operation will be performed with a condensate with tunable interactions. A negligible or weakly attractive value of the interactions will be used to suppress interaction-induced decoherence or create dispersionless wavepackets. As a result, high sensitivities are expected for such interferometer. In a second phase of the project, we will demonstrate a Sagnac-like interferometer with non-interacting condensates propagating in a close circuit. This will realize a guided atom gyroscope whose achievement has been a long-standing goal, and which finds an important application in inertial navigation. Finally, we will generate mesoscopic optical tweezers for realizing a dynamical double-well potential for Mach-Zehnder interferometry. By moving the tweezers apart we will control the coupling between the two wells, and by setting strong repulsive interactions we will produce optimally spin-squeezed states.