Knowing one's location on Earth is simply a matter of opening a Maps application on a smartphone. This is made possible by the availability of the Global Positioning Satellite (GPS) infrastructure. Knowing a spacecraft's position in interplanetary or deep space, however, is a considerably more difficult challenge. Spacecraft position information is presently obtained primarily using radio signals sent between the vehicle and radio transmitters on Earth, and sometimes by radio signals sent from the craft to a nearby object, such as a planet or other large object. Such radiometric position sensing is costly and slow. This research project, a collaboration between quantum physicists, aerospace engineers, and control systems engineers, centers on the development of new quantum technology that uses atoms as very precise inertial sensors to measure accelerations and rotations of a spacecraft. Specifically, the new quantum technology uses atoms that are confined and manipulated by laser beams forming an optical lattice. Combined with a highly-accurate atomic clock, the atomic inertial sensor serves as the core of a navigation system that does not need any external references such as radio signals or images to provide position information. Because atoms have mass, they are directly affected by forces that cause a vehicle to accelerate and or rotate. Using quantum superposition, the researchers take advantage of the quantum wave properties of atoms to measure these forces very precisely. In interplanetary space, even the forces of impact of very tiny asteroids can add up to change the trajectory of a spacecraft significantly over time: no current technology is precise enough to track such small forces. To know completely the position of a spacecraft that passes near a massive body one must account for the effects of gravitational forces. This is done by measuring acceleration forces on atoms at the same time at different places within the spacecraft. Gravity gradiometry also provides a significant means of monitoring the health of the Earth: for example, the Earth's gravity field changes with shifts in the polar ice masses. This research in new quantum technology is thus likely to lead to improved tools for Earth monitoring as well as greatly facilitating space travel.
This research employs basic science and engineering toward the advancement of optical atomic lattice-based inertial sensing for measuring acceleration, rotation, and gravity, collectively referred to as inertial sensing. Quantum technology is widely acknowledged to hold disruptive potential in applications of interest to national security, science, and commercial industry. Navigation in a GPS-denied environment, for example, is currently of great concern for the armed services. In some cases, inertial sensors based on atom interferometry offer orders-of-magnitude improvement in performance compared to classical technologies such as ring laser and fiber gyroscopes. Indeed, laboratory systems have exhibited groundbreaking performance. This work envisions applications where significant size constraints are at play and the environment is sometimes highly dynamic. To address such practical considerations, the investigation focuses on advanced inertial sensors based on optical atomic lattices. An optical lattice is produced using interfering pairs of laser beams to confine laser-cooled atoms in periodic structures. Optical lattices can confine atoms with accelerations of many g (the gravitational acceleration at the Earth's surface). New methods for manipulating the quantum state of ultracold atoms by modulating the laser beams forming the optical lattice will provide a pathway to an entirely new class of quantum-enabled atom interferometric inertial sensors capable of operating in a dynamic environment while maintaining a small form factor. Key innovations will evolve from combining a deep understanding of the many-body physics of atoms in lattices with the development of feedback-and-control methods that can be used to optimally tailor the inertial sensor response to a given sensing scenario. The domain of this work focuses on space applications such as monitoring of the Earth's gravity and navigation of satellites in deep space. A primary purpose of this research is the evolution of optical atomic lattice sensors from a purely scientific endeavor to an engineering one. Strategically, this work represents the first milestone of an inertial sensing quantum technology roadmap. The high-level goal of this effort is to establish a sensor prototype facility that will be made available to future generations of students and to industry as a platform on which to develop and test sensor concepts. Over time, other critical classical engineering disciplines will be brought into a collaborative effort to advance the overall state-of-the-art at the system level.
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.
