The relative phase of first ( ω 1 ) and third harmonics 3 extreme ultraviolet light pulses was varied to control the population 2 s </...

Although interference is intrinsically a classical wave phenomenon, the superposition principle which underlies all interference is also at the heart of quantum mechanics. Feynman has referred to interference as really ‘‘the only mystery’’ of quantum mechanics. Furthermore, in some interference experiments we encounter the idea of quantum entanglement, which has also been described as really th...