Quantum sensing readies to be the 21st century's surveillance leap

• Quantum sensors can measure minute changes in the environment and could one day be used to detect objects underwater or underground, or to provide navigational information if GPS is knocked out or not available.
• They could also play a key role in creating practical quantum computing.

How it works: Like quantum computers, quantum sensors are built on quantum bits, or qubits.

• Qubits can be manufactured or naturally occurring photons, ions and neutral atoms that can act as these information-gathering and -carrying bits.
• Unlike quantum computers that, at useful scales, will require hundreds of thousands of precisely controlled qubits protected from the environment, quantum sensors take advantage of the fragility of those quantum states to extract information from the environment.
• They generally use two properties of quantum mechanics — superposition and entanglement — to measure changes in rotation, pressure, gravity and magnetic or electric fields.
• Atomic clocks used for GPS are quantum-sensing timekeepers and magnetic resonance imaging (MRI) measures changes in the quantum mechanical properties of hydrogen atoms to create medical images.

What's happening: Quantum sensors are being developed for a range of applications from smart building monitoring and oil prospecting to intelligence gathering and navigation. These devices, which are in general more precise than their classical counterparts, include next generation atomic clocks as well as:

• Quantum gravimeters: When mass decreases, so does gravity — an often subtle change that these devices can measure. They could be used to discover underground tunnels or water, new oil fields or precious metals that have different densities. They can measure these changes at the level of a centimeter and are "very, very sensitive," says Michal Krelina, a quantum security consultant at EU Agency for the Space Programme (EUSPA), but they aren't good for spotting something small, he adds.
• Quantum inertial navigation: Quantum-based measurements of acceleration, rotation and time could provide extremely accurate positioning information that doesn't drift like existing classical devices. It might allow nuclear submarines to remain underwater rather than surface every few days to sync with GPS.
• Quantum radio frequency sensors: Leveraging quantum properties, these devices aim to use one receiver tuned to many frequencies across the spectrum. That would allow multiple receivers to be packed into a device smaller than the 6-foot-tall antenna on top of cell towers today, says Bob Sutor of quantum technology startup Infleqtion, which is developing quantum RF antennas.
• Some of these technologies, like navigation systems, may be ready in two to five years, Krelina predicts, whereas others may be 10 years out.

Where it stands: Quantum sensing devices are being developed and tested outside of the lab by militaries and companies around the world.

• The U.S. Air Force recently awarded SandboxAQ a contract to develop its quantum navigation technology that the company says would act as a complement to GPS. The plan is to demonstrate the technology on U.S. Air Force aircraft.
• Other companies — including Rafael Advanced Defense Systems in Israel and Q-CTRL in Australia — as well as NATO, the U.S., China and other militaries are developing quantum sensing devices.

The intrigue: Quantum sensors can be tested on satellites, drones and aircraft.

• But stratospheric balloons offer advantages: "they have amazing line of sight. It's really cheap to launch it alone, versus sending a satellite or plane up," Sutor says. And, "it's very gentle."
• Infleqtion and WorldView, which uses balloons to study Earth's stratosphere, recently announced a partnership to test quantum sensing technology on the platform.

The big picture: Seventeen nations spent an estimated $30 billion last year on their national programs to develop quantum computing, communications, cryptography and sensing, according to the World Economic Forum.

• China, which accounts for about half of that global investment, has launched satellites dedicated to quantum communications and reports passing key computing milestones.

What to watch: Quantum sensors will encode lots of quantum data.

• That data generation could actually fuel the development of quantum computing by offering those systems information that is already in quantum form, Sutor says, overcoming the problem of converting classical data into quantum data for computing.
• Quantum sensing progress requires making the devices smaller and less expensive. A non-scientific challenge is a good supply chain, especially for lasers that are used to control qubits, he says.