Spin qubits based on interacting spins in double quantum dots have been successfully demonstrated. Readout of the qubit state involves a conversion of spin to charge information, universally achieved by taking advantage of a spin blockade phenomenon resulting from Pauli's exclusion principle. The archetypal spin blockade transport signature in double quantum dots takes the form of a rectified current. Currently more complex spin qubit circuits including triple quantum dots are being developed. Here we show both experimentally and theoretically (a) that in a linear triple quantum dot circuit, the spin blockade becomes bipolar with current strongly suppressed in both bias directions and (b) that a new quantum coherent mechanism becomes relevant. Within this mechanism charge is transferred non-intuitively via coherent states from one end of the linear triple dot circuit to the other without involving the centre site. Our results have implications in future complex nano-spintronic circuits.
@article{arxiv.1310.5269,
title = {Bipolar spin blockade and coherent state superpositions in a triple quantum dot},
author = {M. Busl and G. Granger and L. Gaudreau and R. Sánchez and A. Kam and M. Pioro-Ladrière and S. A. Studenikin and P. Zawadzki and Z. R. Wasilewski and A. S. Sachrajda and G. Platero},
journal= {arXiv preprint arXiv:1310.5269},
year = {2013}
}