The difference between Majorana fermions and Dirac fermions can be expressed mathematically in terms of the creation and annihilation operators of second quantization: The creation operator formula_1 creates a fermion in quantum state formula_2 (described by a "real" wave function), whereas the annihilation operator formula_3 annihilates it (or, equivalently, creates the corresponding antiparticle). For a Dirac fermion the operators formula_1 and formula_3 are distinct, whereas for a Majorana fermion they are identical. The ordinary fermionic annihilation and creation operators formula_6 and formula_7 can be written in terms of two Majorana operators formula_8 and formula_9 by