When can you detect quantum coherence at macroscopic scales ?
The macroscopic quantum coherence ( Off - Diagonal Long - Range Order , ODLRO ) & Onsager ( 1957 ) , C. N. Yang ( 1962 ) for laser light , and superfluidity , is related to first - order ( 1 - body ) coherence / ODLRO , while superconductivity is related to second - order coherence / ODLRO .