Pulsed Quantum Optomechanics with a Particle in a Magneto-Gravitational Trap

Montana State University, Bozeman MT

Investigators

Abstract

The project will experimentally investigate a fundamental question in physics: What is the largest size scale explained by quantum mechanics, the theory of physics that has led to computers, smartphones, light-emitting diodes (LEDs), and lasers? While quantum mechanics correctly predicts the behavior of small objects such as electrons and atoms, the application of quantum mechanics to larger objects has puzzled physicists for over 80 years. Most famously, applying the often strange predictions of quantum mechanics to the macroscopic objects we experience in daily life led the famous physicist Erwin Schroedinger to conclude that a cat could be placed in a state in which it is both dead and alive at the same time! In the present project, the investigators will test the predictions of quantum mechanics on a small sphere, approximately 1 micrometer across, which is 10,000 times larger than an atom but still 100 times smaller than the diameter of a human hair. To isolate the sphere, it will be levitated in a magnetic field in a sealed chamber with nearly all the air removed; less than one millionth of one millionth of atmospheric pressure will remain. Since nothing is allowed to directly touch the sphere, it will be pushed around using laser light. Ultimately, the behavior of the sphere under these conditions will increase our understanding of the limits of quantum mechanics, which makes much of modern life possible. This goal of this project is to test the predictions of quantum mechanics on a mesoscopic object, a micrometer-scale sphere levitated in a magneto-gravitational trap. The project builds on the unique properties of a microsphere in a magneto-gravitational trap, including static trapping fields, stable trapping, extreme isolation from the environment in ultra-high vacuum, high efficiency of optical detection of the particle position, and the precise control of the motion of the particle which is possible with feedback cooling via radiation pressure. While the motion of the particle is classical over long time scales (seconds), new sub-millisecond pulsed measurements with greatly increased optical intensity are predicted to reveal quantum-limited behavior when the radiation pressure shot noise due to the illumination dominates the motional state decoherence. In particular, the pulsed measurements are expected to enable position detection near the standard quantum limit. With continued improvements in isolation, the system will enable tests of gravitational collapse models such as continuous spontaneous localization and serve as a platform for future exploration of mesoscopic quantum mechanics and ultra-sensitive force measurements. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.