PNT technologies involve applying quantum sensors and clocks to determine where in the world we are at any given time. A common form of navigation makes use of satellite networks in space to beam down your location to your phone or car’s map. These satellite signals are quite easily disrupted however, and so it is important to be able to navigate independently of them. There are multiple methods to do this. One important one is to use accelerometers and gyroscopes to measure how fast you speed up or rotate and a clock to time how long you have been accelerating or rotating for. These measurements can then be combined to determine exactly how far you have moved.
The next-generation quantum PNT systems are poised to ensure that planes, vehicles and ships can independently navigate with greater precision and for longer periods than ever before.
Quantum PNT is about ensuring that state-of-the-art quantum sensors and clocks, using atomic references, can be deployed to improve the precision with which we all navigate the world.
With three accelerometers (left-right, up-down, forward-backward), three gyroscopes (roll, pitch, yaw), and a clock, it is possible to determine how far a platform has moved and in what direction it is moving.
An atomic spin gyroscope (ASG) measures rotation by using the quantum property of atoms known as spin. Inside the sensor, atomic spins act like tiny reference points. As the device rotates, those spins shift in a predictable way, creating a measurable change in spin frequency.
By using lasers to prepare and read out the atomic spins, scientists can detect small rotations. Because atoms behave in a highly stable and repeatable way, ASGs can be extremely accurate with low drift. This makes them useful for navigation systems, especially in situations where GPS signals are not available, such as underground, underwater or in space.
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Caption: Just a few cm of water will block GPS signals, hindering underwater navigation
NPL has miniaturised atomic fountain clocks, the gold standard for time measurement, reducing their volume by a factor of 20 compared to NPL’s caesium fountain primary frequency standards, whilst still achieving stability of one part in 10¹⁵ after several days of averaging, comparable to full-scale systems.
A fountain clock derives its precision from the time atoms spend between passes through a microwave cavity on their way up and down in the fountain.
Simplified optics, shrinking the physics package and the use of commercial fibre-coupled components enable low maintenance and high uptime, suitable for practical real-world environments beyond the research laboratory.
NPL is also developing lattice atomic clocks that use ultra-stable lasers and high-accuracy cold atom and ion systems that will lead to miniature optical frequency atomic clocks.
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Caption: At the heart of an optical atomic clock - NPL designed the cavity comprising two highly reflective mirrors which are optically contacted to an ultra-low-expansion glass spacer, so they form a standing wave cavity for light waves.
Quantum-based navigation can enable planes, trains, vehicles and ships to independently and autonomously determine their location with greater precision than is currently possible. This means they can operate reliably and robustly over much longer periods of time and do not get disrupted by drops in satellite signals.
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Caption: PNT could help planes navigate autonomously.
Quantum PNT technologies connect directly to several A level Physics ideas. These include wave-particle duality, because atoms can behave like waves; interference, because the sensor compares wave paths; photon momentum, because lasers are used to control the atoms; and fields and forces, because gravity, motion and magnetism all affect the measurement. This makes quantum PNT a strong real-world example of how ideas from classroom physics feature in advanced research.
Transforming global positioning, navigation and timing - NPL
Compact atomic clocks - NPL
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