Phys. Rev. B (in the press); preprint at

The technique of interferometry — using interference to extract information — provides us with the ability to ‘see’ on incredibly small scales. Various applications, ranging from single-photon sensing to gravitational-wave detection, are based on the same idea that small changes in length, for example, can be converted into a relative phase. Now Yuto Ashida and co-workers have proposed a new one: using interferometry to probe magnetic polarons.

The scheme involves a system containing an impurity atom immersed in a two-component Bose–Einstein condensate. The interaction between the impurity and bath atoms gives rise to the formation of magnetic polarons, whose presence in turn slightly modifies the spin-wave excitations inside the condensate. Applying interferometry to the bath atoms, these spin-wave excitations are converted into spin dephasing. In this way, the tiny impact caused by the polarons can be determined from the interference fringes. The scheme offers an alternative route to observe few-body physics beyond conventional spectroscopy.