The p-Orbital Qubit in the Presence of Valley Orbit Coupling

This work builds upon a recently proposed charge qubit [Caporaletti & Kestner, Phys. Rev. Lett. (2025)] encoded in the single-electron, p-like valence states of a five-electron Si quantum dot, which couples to charge noise through the quadrupole moment. We theoretically demonstrate that alloy disorder in the quantum well of a Si/SiGe heterostructure couples the p-orbital subspace to the valley subspace with an order of magnitude of GHz. This expands the original p-orbital picture to a new four dimensional Hilbert-space, allowing for new qubit encodings. Specifically, we consider encoding the qubit in an energetically separated manifold where the valley and p-orbital states are mixed. This encoding enables sweet spots which are first order insensitive to even quadrupolar electrical noise (boosting the dephasing time from 100 ns to 1-10 μs). We also find that two-qubit Coulomb interactions are ZZ in nature, with a fully tunable sign and magnitude. We examine benefits of the sweet spot and tunable two qubit gating in the context of qubit scalability.