Researchers describe a new strategy for creating entanglement that takes into account the spin-squeezing effect. The ability to create quantum entanglement in planar magnets will make quantum sensors smaller and simpler.

Quantum sensors allow scientists to measure things that previously seemed impossible: the oscillations of atoms, the properties of individual photons, the fluctuations associated with gravitational waves. Quantum mechanics makes it possible to create “spin compression” in a material. It’s a promising method that could dramatically increase the accuracy of the world’s most sensitive quantum sensors, but it’s incredibly difficult to implement. In a new study, physicists have described how they’ve made spin compression more accessible.

Spin compression is a form of quantum entanglement that confines the oscillations of a collection of particles. This allows for more accurate measurement of some observed signals, but also reduces the accuracy of measurements of additional signals.

An interconnected system is like a fully inflated balloon. The sphere symbolizes the uncertainty inherent in any quantum dimension. Scientists are “squeezing” this uncertainty, increasing the height but decreasing the width. The sphere changes shape to an ellipse, and the precision of measurements of one type of signal increases.

Quantum entanglement researchers assumed that spin compression was only possible in “all-to-all” systems. But recently, an international group of scientists showed that it can also occur in locally interacting flat magnet systems. Their research was published in the journal Nature Physics.

The Harvard team’s work builds on a landmark 1993 paper that first described the possibility of creating a spin-squeezed entangled state through interactions with everything between atoms. Such a connection easily allows the quantum mechanical correlations needed to create a squeezed state to build up. In nature, however, atoms typically interact, so only a few neighboring atoms interact at a time.

Researchers have described a new strategy for creating spin compression entanglement. They hypothesized and quickly confirmed with experiments that all the elements and conditions necessary for spin compression are present in ferromagnetism, a common type of magnetism. It does not require extreme conditions, occurs in nature, and is responsible for the attraction of magnets to steel.

The data confirm that an “all-in-all” interaction is not necessary to achieve spin compression. Additionally, spin compression can be generated dynamically if the spins are coupled well enough to synchronize to a magnetic state.

The researchers are optimistic that spin compression could enable more portable sensors for biomedical imaging and atomic clocks.

The next step will be experiments to create spin compression in quantum sensors by relying on a defect in the crystal structure of diamond. The experiment used a spin compression analog to increase the sensitivity of gravitational wave detectors. LIGOHe was awarded the Nobel Prize in 2017 for his creation.