Certain one-dimensional Fermi systems have an energy gap in the bulk spectrum while boundary states are described by one Majorana operator per boundary point. A finite system of length $L$ possesses two ground states with an energy difference proportional to $\mathrm{exp}(-L/l_0)$ and different fermionic parities. Such systems can be used as qubits since they are intrinsically immune to decoherence. The property of a system to have boundary Majorana fermions is expressed as a condition on the bulk electron spectrum. The condition is satisfied in the presence of an arbitrary small energy gap induced by proximity of a three-dimensional p-wave superconductor, provided that the normal spectrum has an odd number of Fermi points in each half of the Brillouin zone (each spin component counts separately).

RT Journal
T1 Unpaired Majorana fermions in quantum wires
A1 Kitaev,A.Yu.
PB Успехи физических наук
PY 2001
FD 10 Sup, 2001
JF Успехи физических наук
JO Усп. физ. наук
VO 171
IS 13
SP 131-136
DO 10.1070/1063-7869/44/10S/S29
LK https://ufn.ru/ru/articles/2001/13/ac/