  The experimental realization of Majorana fermions presents an important
problem due to their non-Abelian nature and potential exploitation for
topological quantum computation. Very recently Sau et al. [arXiv:0907.2239]
demonstrated that a topological superconducting phase supporting Majorana
fermions can be realized using surprisingly conventional building blocks: a
semiconductor quantum well coupled to an s-wave superconductor and a
ferromagnetic insulator. Here we propose an alternative setup, wherein a
topological superconducting phase is driven by applying an in-plane magnetic
field to a (110)-grown semiconductor coupled only to an s-wave superconductor.
This device offers a number of advantages, notably a simpler architecture and
the ability to tune across a quantum phase transition into the topological
superconducting state, while still largely avoiding unwanted orbital effects.
Experimental feasibility of both setups is discussed in some detail.
