Measures even more accurately – News physics and quantum computation

Atomic walls are the best sensors humanity has ever built. Today, they are found in national standardization institutes or on satellites of navigation systems. Researchers around the world are working to further optimize the accuracy of these watches. Now a research team led by Peter Zoller, a theorist from Innsbruck, Austria, has developed a new concept that can be used to operate sensors with even greater precision, regardless of the platform used to manufacture the sensor. “We answer the question of how accurate a sensor can be with existing control options, and give a recipe for achieving it,” explains Denis Vasilyev and Raphael Kaubrügger from Peter Zollers group at the Department of Optics quantum and quantum information at the Austrian Academy of Sciences in Innsbruck.

To do this, physicists use a method derived from quantum information processing: Variable quantum algorithms describe a circuit of quantum gates that depends on free parameters. Thanks to optimization routines, the sensor autonomously finds the best settings for an optimal result. “We applied this technique to a metrology problem – the science of measurement,” Vasilyev and Kaubrügger explain. “It is exciting because advances in atomic physics have historically been driven by metrology, and in turn, quantum information processing has come out of it. So we have come full circle here,” says Peter Zoller enthusiastically. With the new approach, scientists can optimize quantum sensors to the point where they achieve the best technically acceptable accuracy.

Better goals with a little extra effort

For some time it has been understood that atomic clocks could work even more precisely by utilizing the entanglement of quantum mechanics. However, there has been a lack of methods to achieve robust entanglement for such applications. Innsbruck physicists now use a tailor-made jumble that is precisely tuned to the demands of reality. With their method, they generate exactly the combination of quantum mode and measurements that is optimal for each quantum sensor. This brings the accuracy of the sensor closer to the optimum according to the laws of nature, with only a slight increase in overhead. “In the development of quantum computers, we learned to create bespoke tangled states,” explains Christian Marciniak of the Department of Experimental Physics at the University of Innsbruck. “We are now using this knowledge to build better sensors.”

Demonstrate the quantum advantage of sensors

This theoretical concept was first put into practice at the University of Innsbruck, as the research group led by Thomas Monz and Rainer Blatt now reports in Nature. The physicists performed frequency measurements based on variation quantum calculations on their ion trap quantum computer. Since the interactions used in linear ion traps are still relatively easy to simulate on conventional computers, the theoretical colleagues were able to verify the necessary parameters on a supercomputer at the University of Innsbruck. Although the experimental setup is by no means perfect, the results agree surprisingly well with the theoretically predicted values. Since such simulations are not possible for all sensors, the researchers demonstrated another approach: the methods used to automatically optimize parameters without prior knowledge. “Similar to machine learning, the programmable quantum computer finds its optimal state autonomously as a high-precision sensor,” says experimental physicist Thomas Feldker, who describes the underlying mechanism.

“Our concept makes it possible to demonstrate the advantages of quantum technologies over classical computers on a problem of practical interest,” emphasizes Peter Zoller. “We have demonstrated a crucial component in quantum amplified atomic clocks with our varied Ramsey interferometry. Running this in a dedicated atomic clock is the next step. What has so far only been shown for calculations of dubious practical relevance could now be demonstrated with a programmable quantum sensor in the near future – quantum advantage. “

The research was financially supported by the Austrian Science Foundation FWF, the Research Promotion Agency FFG, the European Union under the Quantum Flagship and the Federation of Austrian Industries in Tyrol, among others.

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Materials supplied by University of Innsbruck. Note: The content can be edited for style and length.

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