Profound change could be ahead for airborne reality capture and mapping, in the realm of quantum physics.
The term “quantum leap” is often used loosely to describe excitement over new technologies. This time, though, the “quantum” part is literal—specifically, “quantum sensing.” In this case, it is the leveraging of quantum physics, quantum mechanics, particle states, and properties to improve foundational geodesy, sensors, systems, and methods.
Experimental quantum lidar (right), capturing high detail, even in turbid underwater conditions. Source: Heriot-Watt University
R&D, and in some cases, productization is underway for quantum state-based sensors. Such developments could bring benefits for the following:
- Magnetometry for mapping, positioning, and navigation
- Accelerometers and gyros for navigation, monitoring, and solution stabilization
- Full spectrum antennas for secure communications and multi-band radar
- Radar, lidar, and imaging
- Computing for “big data” processing, classification, and analysis
Aerial mapping has already benefited from a great example of particle physics: Single Photon Lidar. SPL can be advantageous in many situations, and disadvantages in others. While SPL can work at a single particle level, not all implementations interrogate quantum states; not in the manner of the cold matter and Rydberg atom techniques we’re about to examine.
QUANTUM VS. CLASSICAL PHYSICS
Atoms are more like erratic blobs of unstable sub-atomic particles that can have wave-like behaviors, and not like the tidy diagrams of orbiting particles in school textbooks. However, this seeming chaos and varied states (normal and induced) provide boundless opportunities for quantum computing and spatial measurement techniques, such as interferometry, gravimetry, imaging, radar, and lidar. Credit: Gavin Schrock
In the early 20th century, quantum physics underwent a pivotal period of discovery and understanding. Great minds theorized about a fuzzy universe where certain elements of classical physics might not apply. For example, how “uncertainty” becomes one of the keys to a new frontier in scientific understanding. The rejection of many foundational elements of classical physics in the new quantum realm was controversial; Einstein himself insisted that much of classical physics did apply, while others vociferously disagreed (and were later proven to be on the right track).
Quantum computing, while garnering a lot of airplay in the general media, is not to be confused with quantum sensing. The former leverages certain
elements of quantum physics but does not play a direct role in how quantum sensors work. Instead, quantum sensors employ two key concepts that could make many sensor types dramatically more sensitive and capable: cold matter and excited atoms. Plus, there is great promise for multi-sensor stacks.
Quantum physics concepts such as “superposition,” “entanglement,” “squeezing,” “cold matter,” and even “teleportation” (no, it is not related to futuristic dreams of beam transporters), would take volumes to cover… read an expanded version via the link at the end.
THE COLD AND THE EXCITED
One approach to quantum magnetometry for navigation is to use enhanced quantum sensors to detect positions relative to Earth magnetism models. Precision could meet many course navigation, like for ships and aircraft, but could not replace GNSS for precise positioning. Source: NOAA
Cold is cool, literally. Cooling with lasers is the mechanism. This makes matter slower, compared to the speed of light. And colder, in ranges where the Kelvin scale is used.
Atoms are more like erratic blobs of unstable sub-atomic particles that can have wave-like behaviors, unlike the tidy diagrams of orbiting particles in school textbooks. However, this chaos, wave behaviors, and varied states (normal and induced) provide boundless opportunities for quantum interferometry and inertial applications.
The other key concept is Rydberg Atoms. When an atom is excited by a laser, a photon or electron can enter a state where its orbit is expanded and isolated from others nearer the core. These isolated particles become quite sensitive, and their states are observed to enhance applications like magnetometry, radar, lidar, and imaging.
A challenge facing cold matter techniques is miniaturization; vacuum pumps and large shielded chambers are needed. Rydberg Atom approaches are much less expensive and easier to miniaturize, and we will likely see sensors leveraging these sooner for geomatics and aerial mapping.
QUANTUM LIDAR AND IMAGING
Beyond SPL, there is R&D underway for approaches that interrogate the state of photons, including, for instance, spin behaviors and two-photon interference techniques.
Exciting work is being done with entangled particles. Imagine sensors that are not analyzing received photons, but instead, detecting the state of distant entangled photons. There have already been demonstrations of, for instance, a lidar system that can detect high detail, even in turbid water.
QUANTUM MAGNETOMETRY AND NAVIGATION
Magnetic surveys would benefit from enhanced sensors and would also be key to creating more detailed magnetic maps that would be needed for proposed magnetometry-based navigation. The concept is to have very detailed mag maps and readings from super-sensitive magnetometers to determine coarse position and heading.
Dr. Darmindra Arumugam, group supervisor, senior research technologist, and program manager at Jet Propulsion Laboratory, Caltech said, “The key for radar is to tune to the state that it’s in. If it was more sensitive, it could reach all of those bands. So, atom-based techniques like Rydberg radar are focused on tuning. You tune the atom differently, and it’s now sensitive enough for this-or-that band—you can make very sensitive detectors that cover MHz up to THz—it’s just mind-blowing because it changes the game on how radars are done today. As a result, there’s a lot of activity on this topic and I’m leading a large team developing these techniques.” Credit: Gavin Schrock
While this idea is often floated as an alternative to GNSS-based navigation, in reality it would be very imprecise. Sure, it could yield a “ship scale” position but never anything close to ground control point positions. Where it would augment GNSS is as a “canary in a coal mine,” detecting large changes that might be due to spoofing (though rare outside of conflict zones: gpsjam.org).
QUANTUM INERTIAL NAVIGATION
Some fascinating devices have been developed and deployed on ships and submarines, and tested on trains. Because these are cold matter systems, size and weight is an issue, for now. Again, these might serve to detect compromised GNSS positions.
QUANTUM GRAVIMETERS
Gravity is an acceleration, and there are already quantum gravimeters, that use interferometric techniques. “The advantage of using a quantum gravimeter is that the atoms act as an internal calibration reference for everything: the time between light pulses, the frequency of the laser light, even the spacing of our “optical ruler” in the matter-wave interferometer,” said Dr. Brynle Barrett, Associate Professor, Quantum Sensing Ultracold Matter Lab at the University of New Brunswick. “What’s more,” explained Barrett, “is that you can stack two or more to determine a gradient.”
There are already commercial models deployed on the ground, on the water, and in the air (despite being bulky and heavy). They have also been used for underground feature detection, like tunnels. Nasa-JPL for instance, is also researching quantum gravity as a way to navigate in space.
QUANTUM RADAR
An experimental quantum antenna, using Rydberg atom techniques, that can detect the RF spectrum from 0 to 100 GHz. Such broad-spectrum antennas could enable compact multi-band radars. Source U.S. Army press release. Credit: U.S. Army
Leveraging the sensitivity afforded through Rydberg Atom techniques, the U.S. Army recently announced a quantum antenna capable of detecting the RF spectrum from 0 to 100 GHz. The potential of similar antenna technologies for multi-band and more compact radars is already being explored.
“One of the big challenges in radars today is that they are not very tuneable systems, and they need to be big because of the antennas,” said Dr. Darmindra Arumugam, program manager at Jet Propulsion Laboratory, Caltech. “And you’d need different antennas for different bands. A multi-sensor package might benefit from having different radars in different bands.” Consider, for instance, foliage penetrating radar (FOPEN or FOLPEN), airborne multi-band InSAR, etc.
QUANTUM COMPUTING
“In the quantum world, when we have two qubits, together they will be in all four states 0, 1, 2, 3 simultaneously with varying probabilities,” said Venkateswaran Kasirajan, author of Fundamentals of Quantum Computing – Theory and Practice, “with this exponential capability, complex problems can be represented easily with fewer numbers of qubits.” This is in contrast to the 0.1 realm of classical bits. For example (as stated by the team at Azure): “It would take a classical computer millions of years to find the prime factors of a 2,048-bit number. Qubits could perform the calculation in just minutes.”
The marine chronometer revolutionized navigation in the early 18th century. On display at the Science Museum in Kensington London. The museum is only a short walk away from the Center for Cold Matter at Imperial College, where quantum navigation is being researched. Credit: Gavin Schrock
While large and extremely costly at this time, quantum computers may, in a not-too-distant future, augment cloud services used for reality capture and airborne mapping.
The science for the potential applications we touched on is proven, and key technologies have been tested. Now comes productization, where timelines can be difficult to predict, but we are already seeing early implementations.
