New regimes of quantum optomechanics using superfluid-filled cavities

Yale University, New Haven CT

Investigators

Abstract

The work supported by this award will seek to deepen the understanding of how light waves can be used to control sound waves, and vice versa. The team will use "optomechanical" control to study the quantum behavior of macroscopic objects. This is an area of particular interest for fundamental science and for potential technological applications. From a fundamental point of view, the laws of quantum mechanics describe a world in which objects may behave as though they are in multiple places at once, and in which measurements unavoidably disturb the object that is measured. These strange effects are most obvious in the behavior of small objects, and tend to become more obscured the larger the object is. Nevertheless, quantum mechanics predicts that these effects can be observed in any object that is sufficiently well isolated from heat and friction, and which is measured with sufficient sensitivity. In this project, quantum effects in the motion of a small volume of superfluid liquid helium will be studied. Superfluid liquid helium can be cooled to exceptionally low temperatures and offers extremely low levels of friction. Additionally, superfluid liquid helium is compatible with ultrasensitive laser-based measurements that are ideally suited to induce, control, and measure the liquid's quantum motion. Studying the quantum motion of macroscopic objects (and liquid objects in particular) will represent important scientific progress, as it will explore long-standing questions about our ability to access and control quantum effects in a new class of objects. It will also allow the team to explore the how to develop superfluid optomechanical devices for applications such as advanced sensing and communications technologies. The goal of the project is to access qualitatively new regimes of quantum optomechanics. Specifically, the team will study non-Gaussian quantum effects in the motion of macroscopic objects, both when this motion can be described in terms of conventional normal modes and when this description breaks down. To accomplish this, they will use optomechanical devices that consist of a miniature Fabry-Perot cavity filled (or partially filled) with superfluid liquid He. The work will build on prior results with similar devices and will combine new conceptual and technical advances in order to realize new capabilities. These advances fall into three categories. First, the team will adapt single-photon and single-phonon detection techniques for use with superfluid-based devices. Second, the team will engineer devices in which the surface waves of a superfluid body couple to the optical modes of a high-finesse cavity. Third, the team will use multimode optomechanical coupling to study the quantum behaviors of systems with strong non-reciprocity and non-trivial topological features. The proposed activity will advance scientific knowledge on multiple fronts. Accessing and controlling non-Gaussian states in optomechanical systems will enable the group to perform a broad class of quantum sensing and information processing tasks that to date have been out of their reach. Providing access to a wide range of distinctly quantum effects in massive objects will also provide a route towards testing specific questions related to quantum gravity, discrete space-time, and modifications of quantum mechanics (such as spontaneous collapse models). Measuring Gaussian and non-Gaussian quantum effects in multimode devices that can be tuned to access non-reciprocal and topologically non-trivial dynamics will also represent an important advance. This is because in the classical regime, the conventional normal mode description of coupled oscillators breaks down in such systems, as do some key aspects of adiabaticity, and it is unclear at present how this breakdown will alter the system's quantum behavior. This highlights the opportunities for discovery that will come from exploring this system.