text: Particles that have undergone this process appear to have imaginary momentums.
full_question: Particles that have undergone this process appear to have imaginary momentums. This phenomenon is analogous to frustrated total internal reflection. George Gamow's explanation of alpha decay models it as this process. The Josephson effect involves the production of a current due to this phenomenon occurring to Cooper pairs. This phenomenon cannot occur in an infinite square well, but can occur in a finite potential well where edges of the wavefunction appear to leak out. For 10 points, name this phenomenon in which a particle with insufficient energy passes through a potential barrier to enter a classically forbidden region. 
first_sentence: Particles that have undergone this process appear to have imaginary momentums.
raw_answer: quantum tunneling