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THE DARPA SOLUTION in quantum research and territory

PDF Excerpt:
“ An epitome of high technology since the middle of the last century has been built on breakthroughs in the fundamental physics of electronic behavior in solids and in the engineering it takes to manipulate
and exploit that behavior. That led to nothing less than the microelectronics and computer revolutions, which in turn have accelerated advances in all other categories of technology while transforming almost all aspects of life and society, including national security.

The relentless miniaturization over the past 70 years of transistors, circuits, and other electronic components has enabled ever more sophistication in the computation, information, communications, and other technologies reliant on predictable electronic behavior. The size of components on chips is so minuscule now that quantum-mechanical effects are becoming both a limiting factor and an opportunity multiplier. In traditional integrated circuits, these quantum effects can reduce the stability of a one or zero state of transistors thereby eroding the technology’s all-important reliability. At the same time, leveraging the strengths of quantum effects can open the way to new defense-relevant capabilities including more secure communications and computations of unprecedented complexities.

THE DARPA SOLUTION
For decades, DARPA’s investments in quantum research has laid the foundation for next-generation
military capabilities such as positioning, navigation, and timing (PNT) in GPS-denied environments; quantum computing; and ultra-secure communications. In the 1990s, DARPA made initial investments for studies into manipulating and measuring the quantum properties of an electron’s spin. These commitments helped
seed the field of spintronics, which became the source of pivotal advances in digital storage technologies. This fundamental research, along with more than a dozen subsequent quantum
science programs, opened pathways to a new generation of quantum sensing technologies. These have included ultraprecise timing, inertial measurement for precise position and motion sensing, and magnetic and electric field sensing. For example, the Chip-Scale Atomic Clock (CSAC) program (2001-2009) created a miniaturized, low-power, time and frequency reference unit. Compared to traditional atomic clocks, those that evolved under the CSAC program achieved a 100-fold size reduction while consuming 50-times less power and spawned commercially available CSAC technology.

Such a capability could greatly reduce one of the more worrisome national security vulnerabilities: a deep and growing dependence on the Global Positioning System’s (GPS) time reference signals. These master clocks at the heart of GPS have become pivotal components of the technological infrastructure not just within the military but also throughout the civilian sectors of the economy, from banking to telecommunications to the power grid. That’s because the timing signals from satellite-based atomic clocks provide the key reference signals for synchronizing atomic clocks in use on the ground. The longer those clocks on Earth or on aircraft can maintain extreme accuracy in the absence of satellite reference signals, the lower the impact of any loss of satellite contact, whether due to natural causes or adversarial activities.

Building on previous DARPA CSAC research, the Atomic Clock with Enhanced Stability (ACES) program, which began in 2016, aims to develop battery-powered CSACs with 1000X improvement in key performance parameters compared to existing CSAC technology. The program is challenging innovators to deliver enhanced- stability clocks that demonstrate size, weight, and power (SWaP) reductions compared to laboratory-proven atomic clock technologies. The program also includes basic research efforts to explore novel component technologies and alternative-physics approaches that
could substantively impact future atomic clock architectures. Related to the ACES program, DARPA’s Atomic Photonic Integration (A-PhI) program calls for the invention of photonic integrated circuits as a tactic to miniaturize the optical atomic clocks developed in the QuASAR program as well as to shrink optical gyroscopes without any sacrifice in performance.
Such advances would open up revolutionary capabilities for GPS-less PNT.

DARPA’s focus on improving time- keeping has gone even deeper into quantum territory. Under the agency’s
All Together Now (ATN) program (2016-2020), researchers have been developing clocks that exploit optical frequencies instead of longer-wavelength microwaves. In this program, DARPA is aiming for optical-based atomic clocks with 1000-times greater stability and precision compared to current timing technology. Today’s microwave-based atomic clocks on GPS satellites provide 10-nanosecond (billionth of a second) timing, whereas optical clocks could provide 10-picosencond (trillionth of a second) precision. This enhanced precision would allow for more robust GPS technology, since devices would require fewer updates. Based on a recent ATN demonstration of an all- optical atomic clock that outperforms all existing clocks, NIST has initiated an effort to develop a new optical time standard.

In this schematic of a quantum dot laser developed by researchers at the University of California, Santa Barbara, a gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs) quantum-dot laser is integrated atop a silicon substrate. On the right, an optical micrograph reveals the distribution of quantum dots.
In this atomic-clock component designed to trap rubidium atoms for precise monitoring, light-guiding channels glow from the light they are directing. The otherwise invisible, intersecting atom-trapping beams ...”