Engineering a new generation of atom interferometers

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.

The proposed research lays at the confluence of fundamental physics and metrological application. It is part of a sustained global effort to understand the underpinning science and turn quantum mechanics into useful technology. Atom interferometry, in particular, is a key research field of future broad relevance, with impact in different fields of Physics also due to the possibility to test fundamental theories, and measure constants (the gravitational constant G, the ratio h/m, etc.). Our project can find immediate application in the search of small-scale deviations of the Newtonian Gravitational law, in the study of atom-surface interactions like the Casimir-Polder force, and for practical use in inertial navigation with a compact device. The impact of our research is thus potentially large, and will be organized according to the following points:

1. Communication and Outreach
Our results will be submitted to the Cornell Arxiv depository and high-impact journals, especially taking advantage of the broader readership reachable by open-access papers. This will guarantee visibility within the relevant physics community. For engaging a wider scientific audience, we will contribute to tutorial, review articles, and to online magazines which report on popular science, research and technology. Given the broad range of applications and scopes of atom interferometry which have already shown to be particularly appealing for the general public (for example navigation without GPS, search for dark energy, and gravitational waves, etc.) and to be regularly covered by the media, we will interact with local/national newspapers and popular science magazines. We will exploit our Cold Atoms group website and online forums to disseminate videos explaining our research activity and results. The University of Birmingham will support me also by providing training to public communication.

2. Collaborations and Networks
This project will greatly benefit from the collaboration with one of the strongest theory groups in the world working on quantum control. We aim at rapidly enlarging our circle of collaborators in UK and overseas, specifically targeting the community working on Quantum Metrology, due to our advantaged platform for the generation of entangled states. Our experimental results and findings will accelerate this process and will help us to consolidate the contacts that we have developed so far. Our work also fits excellently within the scopes of the Atomtronics community. Seminars, presentations and participation in dedicated workshops (like the Atomtronics series) are an ideal vehicle to rapidly spread the impact of our research to the relevant academic community and to foster additional collaborations.

3. People
The proposed project will provide advanced training for two PhD students in the field of atom interferometry, which is a rich interdisciplinary field with applications ranging from tests of fundamental Physics to autonomous vehicle navigation and geodesy. The experimental activity and the synergetic collaboration with a strong theory group will allow the students to develop technical skills and to learn advanced scientific methods in an environment which promotes team building.

4. Application and exploitation
Our work addresses in an innovative way an established field of research, and therefore it is reasonable to estimate that the applications and technological transfer will follow in rather short timescales after the first results of the project appear. We will be supported in capitalizing our achievements by the expertise of the members of the Cold Atoms group involved in the Quantum Hub for Sensors and Metrology, which have already developed valuable connections with a large number of UK companies interested in atom interferometers and related technology. We will also benefit from collaboration with the National Physical Laboratory (where I am currently working on secondment).