Quantum interference of superfluid 3He

Celebrated interference experiments have demonstrated the wave nature of light(1) and electrons(2), quantum interference being the manifestation of wave-particle duality. More recently, double-path interference experiments have also demonstrated the quantum-wave nature of beams of neutrons(3), atoms(4) and Bose-Einstein condensates(5). In condensed matter systems, double-path quantum interference is observed in the d.c. superconducting quantum interference device(6) (d.c. SQUID). Here we report a double-path quantum interference experiment involving a liquid: superfluid He-3. Using a geometry analogous to the superconducting d.c. SQUID, we control a quantum phase shift by using the rotation of the Earth, and rnd the classic interference pattern with periodicity determined by the He-3 quantum of circulation.