Measuring even more precisely — ScienceDaily
Atomic clocks are the best sensors mankind has ever built. Today, they are found in national standards institutes or on the satellites of navigation systems. Scientists around the world are working to further optimize the accuracy of these clocks. Now a research group 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 platform. technique used to manufacture the sensor. “We answer the question of how precise a sensor can be with existing control capabilities, and give a recipe for achieving it,” explain Denis Vasilyev and Raphael Kaubrügger of Peter Zoller’s group at the Institute of Optics quantum and quantum information at the Austrian Academy of Sciences Institute in Innsbruck.
To do this, physicists use a method derived from quantum information processing: variational 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’s exciting because historically advances in atomic physics have been driven by metrology, and in turn quantum information processing has come out of that. So we’ve come full circle here,” enthuses Peter Zoler. With the new approach, scientists can optimize quantum sensors to the point where they achieve the best possible technically acceptable accuracy.
Better measurements with little extra effort
For some time now, it has been understood that atomic clocks could work even more precisely by exploiting the entanglement of quantum mechanics. However, there has been a lack of methods to achieve robust entanglement for such applications. The Innsbruck physicists are now using a bespoke tangle that is precisely tuned to real-world demands. With their method, they generate exactly the combination consisting of quantum state and measurements that is optimal for each individual quantum sensor. This brings the accuracy of the sensor closer to the optimum possible according to the laws of nature, with only a slight increase in overhead. “In the development of quantum computers, we learned how to create tailor-made entangled states,” explains Christian Marciniak from the Department of Experimental Physics at the University of Innsbruck. “We are now using this knowledge to build better sensors.”
Demonstrate the quantum advantage with 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 variational 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 feasible for all sensors, the scientists demonstrated a second approach: they used methods to automatically optimize parameters without prior knowledge. “Similar to machine learning, the programmable quantum computer finds its optimal mode autonomously as a high-precision sensor,” says experimental physicist Thomas Feldker, describing the underlying mechanism.
“Our concept makes it possible to demonstrate the advantage of quantum technologies over classical computers on a problem of practical interest”, emphasizes Peter Zoller. “We have demonstrated a crucial component of quantum enhanced atomic clocks with our variational Ramsey interferometry. Running this in a dedicated atomic clock is the next step. What has so far only been shown for computations of questionable 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 Fund FWF, the Research Promotion Agency FFG, the European Union under the Quantum Flagship and the Federation of Austrian Industries in Tyrol, among others.