Chaos Makes Quantum Sensors Work More Precisely

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Quantum sensors already measure quantities such as temperature, magnetic field strength or accelerations very accurately. And they work even more precisely with chaotic dynamics. Physicists at the University of Tübingen showed this in a study in which they developed a method with which the measurement accuracy of high-precision sensors could be improved by a further 70%. Doctoral candidate Lukas Fiderer and Professor Daniel Braun from the Institute of Theoretical Physics used weak laser pulses in a computer simulation to disturb the dynamics of a magnetic field sensor. The results of the study were published in the journal Nature Communications. 

Quantum metrology is a field of metrology, the science of measurement. It differs from conventional measuring methods as quantum systems such as atoms or photons are employed as sensors that can only be described with the laws of quantum mechanics. Conventional sensors follow regular, predictable dynamics. They are constructed in such a way that chaos – this is how theoretical physics describes dynamics in which disturbances grow exponentially – is avoided, otherwise the measurement of parameters becomes unpredictable or even impossible. But quantum sensors follow other laws: Quantum chaos is not at all associated with unpredictability. 

The scientists therefore investigated how measurement accuracy would change if the quantum sensor did not behave regularly but increasingly chaotically. They used formulas to describe a physical model and then designed a computer simulation of a quantum sensor, the atomic vapor magnetometer, and its dynamics. Atomic vapor magnometers are already very accurate magnetic field sensors which contain a vapor of alkali atoms in a glass cell. When the cell is in a magnetic field, the atoms rotate like small compass needles. By measuring the direction of rotation with a laser, scientists can measure the magnetic field. "In the simulation, we fired weak laser pulses at the atoms during the measurement process to render the dynamics chaotic," explains Lukas Fiderer, who started this research as part of his master thesis and is now working on his doctorate. 

The research demonstrated an improvement in measurement accuracy of 70%. A decisive advantage is that the chaotic dynamics can be set in such a way that the sensor is more robust against disturbing interactions with the environment. The scientists have already applied for a patent for the new magnetic field sensor. “We hope that our model will soon be implemented experimentally and assume that the method will be used in various quantum sensors. It could pave the way forward to more accurate and robust sensors.”