A team of scientists has developed a way to measure magnetic fields using a quantum system, which could mean more precise technology for future sensors.
The researchers, from Aalto University in Helsinki, and MIPT and Landau Institute in Moscow, used this method to achieve accuracy beyond the standard quantum limit and thus believe that their work is a first step towards using quantum-enhanced methods for sensor technology.
They said that their research pushes the limits to how accurately you can measure things and is potentially important in a variety of fields, from geological prospecting to imaging brain activity.
"We wanted to design a highly efficient but minimally invasive measurement technique," explained Sorin Paraoanu, leader of the Kvantti research group at Aalto University.
"Imagine, for example, extremely sensitive samples: we have to either use as low intensities as possible to observe the samples or push the measurement time to a minimum."
The study, published in the prestigious journal NPJ Quantum Information shows how to improve the accuracy of magnetic field measurements by exploiting the coherence of a superconducting artificial atom, a qubit.
In their study, the scientists developed a tiny device made of overlapping strips of aluminium evaporated on a silicon chip - a technology similar to the one used to fabricate the processors of mobile phones and computers. When the device was cooled to a very low temperature, the electrical current flowed in it without any resistance and started to display quantum mechanical properties similar to those of real atoms.
When irradiated with a microwave pulse - not unlike the ones in household microwave ovens - the state of the artificial atom changed. It turns out that this change depended on the external magnetic field applied: measure the atom and you will figure out the magnetic field.
But to surpass the standard quantum limit, another trick had to be performed using a technique similar to a widely-applied branch of machine learning, pattern recognition.
"We use an adaptive technique: first, we perform a measurement, and then, depending on the result, we let our pattern recognition algorithm decide how to change a control parameter in the next step in order to achieve the fastest estimation of the magnetic field," added Andrey Lebedev, corresponding author of the study.
"'This is a nice example of quantum technology at work: by combining a quantum phenomenon with a measurement technique based on supervised machine learning, we can enhance the sensitivity of magnetic field detectors to a realm that clearly breaks the standard quantum limit."
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