Improving the sensitivity of atomic sensors
Researchers with the EU-funded AQUMET project had an ambitious goal in mind: to demonstrate and record the sensitivity of atomic sensors – and then improve on that sensitivity – using quantum physics in general and, specifically, entanglement. Examples of atomic sensors include atomic clocks and atomic magnetometers. What researchers achieved is a truly ground-breaking accomplishment, opening the door for using super-precise measurements in a number of fields. ‘This work is technologically interesting as magnetic fields are omnipresent, and nearly everything either produces or modifies the magnetic field in some way,’ says project coordinator Morgan Mitchell. ‘In practice, having access to super-precise measurements is beneficial to mineral exploration, for example, as it provides access to precise measurements of the earth’s magnetic field as distorted by underground mineral deposits. It also means various biological processes in the heart and brain can now be observed by the magnetic field they produce.’ Squeeze play The sensitivity of an atomic magnetometer is defined by the smallest signal it can reliably resolve, a definition that is fundamentally limited by quantum noise. For example, if a laser detects the atoms and their response to the magnetic field, this sensitivity will be limited by shot noise, otherwise known as the source of the quantum noise. To reduce this shot noise, and thus improve magnetic sensitivity, one can use quantum optical techniques known as squeezing – which is what AQUMET did. ‘Our research demonstrated the first improvements in magnetic sensitivity due to squeezing – both the squeezing of light, where shot noise is reduced, and by squeezing atomic quantum noise,’ explains Mitchell. ‘What we discovered is that quantum noise in atoms is significantly different than quantum noise in light and, by understanding this, we are able to identify several new squeezed states, including macroscopic singlet states and planar squeezed states.’ According to Mitchell, the planar squeezed state is of particular interest as it has been shown to reduce quantum noise in a way that improves the sensitivity of more complicated sensors, including magnetic resonance imagers that need to be able to simultaneously detect multiple atomic properties. Right on time The AQUMET research has proved to be very timely. ‘By studying the quantum limits of atomic sensing and developing new methods to overcome the usual quantum noise limits in these sensors, the project has laid the foundation for the use of quantum sensing technologies in an array of initiatives and sectors,’ says Mitchell. ‘This includes its role in the upcoming EU Quantum Technologies Flagship Initiative and in enabling sensing technologies to benefit medical research.’ Although the project is now closed, researchers continue their efforts to push the fundamental limits of atomic sensing by applying the system developed in AQUMET. Furthermore, the insights gained in AQUMET are now being applied to new physical systems, including small-scale atomic magnetometers used for detecting bio-magnetic fields, and the new squeezed states discovered by AQUMET are being studied for application to other advanced technologies such as atomic clocks.
Keywords
AQUMET, quantum physics, atomic sensing, quantum technologies, sensing technologies