Quantum sensors can provide location information in environments where GPS signals are not available (e.g. underground, underwater, or in denied locations), and can detect electric and magnetic fields with high sensitivity to receive signals or detect other activity. How can we apply these capabilities in military, space, and other arenas?
Several advanced sensing capabilities are critical to US interests. Position, navigation, and timing (PNT) is critical to systems across the government, and the vulnerability of GPS signals to jamming and spoofing requires the development of sensors that provide PNT in the absence of GPS. Measuring the electric-field (E-field) and/or magnetic-field (B-field) signals emanated from an associated object can therefore help us determine its functional state, which is highly beneficial when physical contacts or invasive probes are not feasible or not allowed. Hence, high-sensitivity E-field and B-field detectors will be extremely useful in these applications.
Quantum sensors are typically “best-in-class” for these applications, and there is a strong motivation for both improving their performance and developing component technologies to enable low cost, size, weight, and power (C-SWAP) quantum sensors
The primary quantum sensors for PNT are atom-based devices that are relatively complex, and for them to be implemented into moving platforms, their C-SWAP must be substantially reduced. For example, light-pulse atom interferometers require a complex laser system with multiple optical channels, where each channel will be required to switch on and off, shift its frequency with high accuracy, and actively control its power. Also, the atoms must be contained within a vacuum chamber, and control and power electronics control the laser system, the vacuum system, and the magnetic field at the atoms. Research is needed to drastically miniaturize the laser system, preferably into a photonic integrated circuit. Reducing the SWAP of the vacuum system and eliminating active pumps in the system is also essential and requires research. Many of the atom-based quantum sensors have complex requirements with common themes across them (e.g. lasers and vacuum systems), and research to reduce C-SWAP and increase their tolerance to extreme environments (temperature, vibration, etc.) will enable their adoption into broad-ranging applications.
For electric-field and magnetic-field sensing, the major challenge is the signals at extremely low frequencies (DC or quasi-DC). The conventional electronic sensors suffer from the thermal noise and 1/f noise, and therefore their performance cannot be as good as the electronic state of the art at RF frequencies. Enabled by Atomic-vapor-cell technology, quantum electrometers and magnetometers demonstrate much better sensitivities at DC to quasi-DC regime compared to other existing sensing technologies. For measuring E-field and B-field signals inside a shielded enclosure, a penetrative EM probe has also been experimentally demonstrated by utilizing relativistic effects and the quantum properties of polarized neutrons. There are, however, still great demands for further enhancing their quantum sensing capabilities in field-deployable applications. For technical challenges, we are looking for new coating materials on the inner surface of alkali-vapor cells to reduce the inner-surface electric conductivity for electrometer applications and to increase the spin relaxation time for magnetometer applications. For challenges in advanced quantum approaches, we are looking for novel methods to entangle atomic spins in the same vapor cell or between different vapor cells. We are also seeking a solution for generating non-classical quantum states, such as a spin squeezed state, of neutrons.
Another avenue of research is the continued improvement in the performance of quantum sensors. Miniaturization will often reduce the sensitivity, so techniques to mitigate this need to be researched to enable quantum sensing in mobile applications. Techniques to increase performance can either classical (e.g. technical improvements to increase signal size) or purely quantum (e.g. spin squeezing or entanglement). Simplified techniques to implement spin squeezing or entanglement are particularly interesting.
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