Rashba interferometers: Spin-dependent single- and two-electron interference

Abstract

Quantum transport in semiconductor nanostructures can be described theoretically in terms of the propagation and scattering of electron probability waves. Within this approach, elements of a phase-coherent electric circuit play a role similar to quantum-optical devices that can be characterised by scattering matrices. Electronic analogues of well-know optical interferometers have been fabricated and used to study special features of charge carriers in solids. We present results from our theoretical investigation into the interplay between spin precession and quantum interference in an electronic Mach–Zehnder interferometer with spin–orbit coupling of the Rashba type. Intriguing spin-dependent transport effects occur, which can be the basis for novel spintronic devices such as a magnet-less spin-controlled field-effect transistor and a variety of single-qubit gates. Their functionality arises entirely from spin-dependent interference of each single-input electron with itself. We have also studied two-electron interference effects for the spin-dependent Mach–Zehnder interferometer, obtaining analytical expressions for its two-fermion-state scattering matrix. Using this result, we consider ways to generate two-electron output states for which the Rashba spin-subband quantum number and the output arm index are entangled. Combining spin-dependent interference in our proposed Mach–Zehnder interferometer with a projective charge measurement at the output enables entanglement generation. As our particular scheme involves tuneable spin precession, electric-field control of entanglement production can be achieved.