When Atoms Decide to Sing in Chorus ⚡ экспресс
The superradiant phase transition of a mesoscopic Fermi gas of ^6Li atoms (from tens to thousands) in a high-finesse optical cavity was studied over a wide range of densities. The superradiance threshold depends non-monotonically on density: reaching a minimum when the Fermi wavevector is comparable to the photon recoil wavevector. The minimum corresponds to a crossover between ordering driven by Fermi pressure at low densities and suppression of photon scattering due to Pauli blocking at high densities, consistent with theory. The dependence of threshold and photon number on atom number confirms this interpretation. Additionally, a regime was realized where light-induced forces are opposite for two spin components, creating an ordered phase with spin-density-wave character. The system opens avenues for exploring few-fermion systems with strong, coherent light-matter coupling.
Physicists trapped a cloud of lithium atoms between mirrors. Light bounces inside, like in an echo chamber, forcing the atoms to emit synchronously — resulting in superradiance, akin to a choir where voices merge into a single thunder.
The secret is density. Atoms too sparse can't hear each other; too crowded — fermions start clashing: the Pauli principle forbids them from occupying the same state, like two singers trying to hit the same note. The superradiance threshold behaves cunningly: first it drops, then rises. The ideal is reached when the distance between atoms matches the light wavelength — then neighbors' help turns into jostling. Another surprise: atoms with different 'spin' separate into waves, alternating in stripes. By controlling this pattern, we can create quantum devices with unprecedented sensitivity. Moreover, superradiance gathers light into a single chord, millions of times faster than individual glow — discordant voices become a thunderous strike. The glow was monitored using spectroscopy methods.
🎯 The term 'superradiance' first appeared in astrophysics to describe black hole radiation, and now it's studied in labs with clouds of atoms.