The primary goal of the SIGMA project is to demonstrate a low-SWaP, high-performance single-axis atom interferometer (AI) accelerometer for field use. In addition to conventional inertial measurement units (IMUs), this disruptive quantum sensing technology will be a game changer to the inertial navigation solution due to the state-of-the-art (e.g., strategic-grade) performance and the non-necessity of external signals for accuracy. Although laboratory demos showed the strategic-grade AI performance, there are significant challenges in the development of compact and reliable cold atom inertial sensors operating in dynamic environments. The project aimed at a shoe-box-sized AI accelerometer operating in dynamic environments, enabling accurate inertial navigation without external signals and offering advanced positional awareness. This technology can be widely applied to numerous defense applications as well as the Nuclear Deterrence mission.
The SIGMA project can provide a compact and low-cost cold atom inertial sensor solution to address the above critical need compared to a currently available, sizable strategic-grade IMU solution of $1 million. The SIGMA project organized multidisciplinary R&D teams for optimal scientific and engineering solutions, from high data-rate atom interferometry with in-house grating chips, single laser architecture with integrated photonics, compact and rugged optomechanical packaging, a passively pumped vacuum chamber to AI feedforward algorithm and hardware implementation with AI physics model and AI co-sensor inputs, and time-critical AI control systems. There were three main areas of progress during the program. First, we demonstrated a passively pumped vacuum package with a titanium chamber and sapphire windows. This system can sustain cold atoms, e.g., magneto-optical-trap (MOT) atoms, in a vacuum for more than five months. Second, we developed silicon integrated photonics (SIP) suppressed-carrier single-sideband (SC-SSB) modulators with dual-parallel Mach-Zehnder configuration and four phase modulators at each path. Using the SIP modulators, we can dynamically tune a light frequency during the measurement sequence to demonstrate state-selective atom detection and atom interferometers. Third, we demonstrated the grating-mirror MOT atom interferometry with high data-rate operation.
The SIGMA project developed strategic-grade AI devices that can be fielded for high consequence applications. The team was able to reduce the SWaP requirements of AIs by three to six orders of magnitude while maintaining the exquisite sensitivity of AI device. The deployable AI prototype will lead directly to significant improvements in positional awareness, providing a necessary leap toward navigation that does not rely on external signals. Specifically, atom interferometry provides radically improved acceleration sensitivity, and the system developed under SIGMA will realize extraordinary SWaP savings. This enabled an inexpensive, low volume, and higher accuracy and precision sensor which was available for field use in defense of the national interest. This technology has the potential to provide solutions to traditional challenges in externally aided navigation accuracy, and the technical challenges associated with these solutions.