Suppression of Leakage for a Charge Quadrupole Qubit in Triangular Geometry*

The relatively weak coupling between spin states in spin qubits has spurred a revival of interest in charge qubits, which promises stronger coupling between multiple charge qubits due to stronger long-range Coulomb interaction. Among the proposed charge qubits, charge quadrupole (CQ) qubit is suggested to provide a relatively robust quantum computation by virtue of the logical bases residing in a decoherence free subspace such that leakage state decouples from the manifold [1]. Conventionally, CQ qubit is realized with an electron residing in a lateral triple quantum dot device, yet any fluctuation in tunneling and detuning control causes significant leakage. We propose a strategy to mitigate such destructive coupling by simply implementing the CQ qubit in a triangular triple quantum dot, where the tunneling between the two dots on the edge strongly suppresses leakage, eliminating the need of complex pulse sequences. The reduction of leakage is demonstrated from molecular orbital calculation, in corporation with numerical simulations.

[1] M. Friesen, J. Ghosh, M. Eriksson, and S. Coppersmith, Nature Communications 8, 15923 (2017).