Feshbach resonances are a powerful tool in atomic physics that allow scientists to tune the interactions between atoms in ultracold atomic gases — systems cooled to near absolute zero where quantum effects dominate.
A Feshbach resonance occurs when the energy of two colliding atoms in a “scattering channel” aligns with the energy of a bound molecular state in a different, usually closed, channel. By applying a magnetic field, researchers can adjust this alignment, thereby modifying the strength and nature of interatomic interactions — from strongly repulsive to strongly attractive.
Key aspects of Feshbach resonances include:
- Tunable interactions: The effective scattering length (a measure of interaction strength) can be precisely controlled.
- Creation of ultracold molecules: Near a Feshbach resonance, atoms can be converted into weakly bound molecules.
- Quantum simulation: Enables exploration of exotic quantum phases and strongly correlated systems.
Feshbach resonances have revolutionized the study of Bose-Einstein condensates (BECs) and fermionic superfluids, allowing researchers to simulate condensed matter phenomena and explore the crossover between Bose-Einstein condensation and Bardeen-Cooper-Schrieffer (BCS) superfluidity in a highly controllable environment.