Effects of phonons on the coherence of a charge quadrupole qubit

Many types of qubits are operated in a regime where the energy splittings between qubit states are large. In this regime, phonons can be the dominant source of decoherence. The charge quadrupole qubit, based on one electron in a triple quantum dot, uses a symmetric charge distribution to suppress the influence of charge noise. However, phonons couple the qubit subspace to a leakage state, potentially limiting the qubit’s coherence. We study the effect of phonons considering Larmor and Ramsey pulse sequences and identify favorable operating parameters and temperatures for them. We show that both pulse sequences can be implemented with >99.9% fidelity in the presence of phonons, but care must be taken to operate the qubit in an appropriate parameter range. This work was supported in part by ARO (W911NF-15-1-0248, W911NF-17-1-0274) and the Vannevar Bush Faculty Fellowship program sponsored by the Basic Research Office of the Assistant Secretary of Defense for Research and Engineering and funded by the Office of Naval Research through Grant No. N00014-15-1-0029. The views and conclusions contained here are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office (ARO), or the U.S. Government.