Researchers have developed a method to quickly create NOON states using ultra-cold atoms. These states, which play an important role in metrology and quantum computing, are now becoming accessible through experiments.
Creating quantum superpositions of ultra-cold atoms has long been a major challenge, with existing methods proving too slow to be practical in the laboratory. Researchers at the University of Liège have now developed a new approach that combines geometry with “quantum control” to significantly accelerate the process, opening the door to real-world applications in quantum technology.
Imagine navigating a supermarket with a cart loaded to the brim. The goal is to reach the checkout faster than everyone else without losing items on the tight turns. The key to success is finding the straightest, smoothest path to maintain speed without needing to slow down.
This is precisely what Simon Dengis, a doctoral researcher at the University of Liège, has accomplished. Not in a supermarket, but in the complex realm of quantum physics.
Working with the Quantum Statistical Physics (PQS) group, Dengis developed a protocol for rapidly generating NOON states. “These states, which look like miniature versions of Schrödinger’s famous cat, are quantum superpositions,” he explains. “They are of major interest for technologies such as ultra-precise quantum sensors or quantum computers.”
The obstacle of time
The main challenge? Manufacturing these states normally takes far too long. We’re talking tens of minutes or more, which often exceeds the lifetime of the experiment. The cause? An energy bottleneck, a “sharp bend” in the system’s evolution that forces it to slow down.
This is where the ULiège team breaks new ground. By combining two powerful concepts, counterdiabatic driving and the optimal geodesic path, they have succeeded in “smoothing the road” for atoms. The result: the system can evolve faster without losing the trajectory of the desired state, just like a driver who anticipates a bend by tilting his tray.
“This strategy saves a considerable amount of time: in some cases, the process is accelerated by a factor of 10,000, while maintaining 99% fidelity, i.e. near-perfection of the result,” says Peter Schlagheck, director of the laboratory. Where previously it would have taken around ten minutes to create such a state, the researchers have succeeded in considerably reducing this waiting time … to 0.1 seconds!
Towards practical applications
With this breakthrough, it is finally possible to produce NOON states with ultra-cold atoms. This opens up prospects in quantum metrology (ultra-sensitive measurements of time, rotation, or gravity) and quantum information technologies. Ultimately, these tools could improve instruments such as quantum gyroscopes or miniature gravity detectors.
This research shows how theory and experimentation can come together to make concrete advances in quantum physics. By combining mathematical concepts, fundamental physics, and experimental feasibility, ULiège researchers have made a breakthrough that could well transform ideas that were once theoretical into tomorrow’s technologies.
Quantum superposition and the Noon state
Quantum superposition is the idea that a quantum system (such as an atom, an electron, or a photon) can exist in several states at the same time, as long as it is not observed. The example most often used to explain this concept is Schrödinger’s cat: a cat is locked in a box. According to quantum mechanics, until the box is opened, the cat is both alive and dead. This simultaneous combination of two states is called superposition.
It is only by opening the box to observe it that we ‘force’ nature to choose a state: alive or dead. The NOON states are an example of quantum superposition: all the atoms are in both the left-hand well AND the right-hand well. It is only at the moment of measurement that they are found in one or the other.
Reference: “Accelerated creation of NOON states with ultracold atoms via counterdiabatic driving” by Simon Dengis, Sandro Wimberger and Peter Schlagheck, 10 March 2025, Physical Review A.
DOI: 10.1103/PhysRevA.111.L031301
