Efimov

Efimov is a Russian surname derived from the given name Efim, a form of Timothy. Surnames of this type are common in Russia and among people of Russian heritage.

The most prominent figure associated with the name is Vitaly Efimov, a Russian theoretical physicist who predicted the Efimov effect in three-body quantum systems in 1970. The Efimov effect describes a counterintuitive situation in which, under certain conditions, three particles can form an infinite series of bound states even when any two of them cannot bind by themselves. This phenomenon is especially pronounced when the pairwise interactions are near a resonance, meaning the two-body scattering length is very large.

Efimov states are universal in the sense that their existence and properties depend on broad features of the system rather than on detailed interactions. For three identical bosons, the energies of successive Efimov states follow a geometric progression, with a characteristic scaling factor of about 22.7 between consecutive states in the idealized zero-range limit.

Experiments in ultracold atomic gases, beginning around the mid-2000s, provided the first clear evidence for Efimov states, with observations in cesium and later other atomic species. The Efimov effect has since played a significant role in the study of few-body quantum physics, informing research in atomic, molecular, and nuclear physics and contributing to our understanding of universal few-body phenomena.