Fig. 1: Conceptual scheme of a Bernoulli factory.

a, CCBF where a sequence of classical coins with unknown bias p are processed for producing a new coin with bias f(p) (refs. ^22,44). b, QCBF in which a quoin serves as the input to synthesize a classical one^25,26. c, Fully quantum version where both input and output are general quantum states²⁹.