JETP Letters: issues online

We review recent studies of the spin-dependent tunneling transport via Aharonov-Bohm interferometer (ABI) formed by helical edge states. We focus on the experimentally relevant case of relatively high temperature, T, as compared to level spacing, Δ. The tunneling conductance of helical ABI is structureless in ballistic case but shows sharp periodic antiresonances as a function of magnetic flux - with the period hc/2e - in presence of magnetic impurities. The incoming unpolarized electron beam acquires finite polarization after transmission through the helical ABI provided that the edges contain at least one magnetic impurity. The finite polarization appears even in the fully classical regime and is therefore robust to dephasing. There is also a quantum contribution to the polarization, which shows sharp identical resonances as a function of magnetic flux with the same period as conductance. This polarization survives at relatively high temperature. The interferometer can be described in terms of ensemble of ${\cal N} \simeq T/\Delta$ flux-tunable qubits giving equal contributions to conductance and spin polarization. Hence, with increasing the temperature number of active qubits participating in the charge and spin transport increases. These features of tunneling helical ABI open a wide avenue for applications in the area of quantum computing.