Triple-Quantum-Dots with Overlapping Gates for Si/SiGe Qubits

Silicon is an attractive host material for quantum bits due to its spinless isotope ²⁸Si, and weak spin-orbit coupling, allowing for long spin decoherence and relaxation times. A state-dependent dipole moment is inherent in many silicon-based qubits, aiding in fast gate times and strong two qubit interactions. However, these types of qubits are susceptible to the decohering effects of charge noise. We present data from devices with potential to reduce the effects of charge noise by making use of symmetry in the quantum dot layout. Of particular interest is the charge quadrupole qubit. A linear triple-dot with a locally integrated charge sensor is used to explore the charge quadrupole qubit. The linear triple dot device utilizes a three-layer overlapping aluminum gate architecture, which has the potential to reduce charge noise due to a terraced field oxide with less bulk oxide in the active region. This architecture allows for high tunability of tunneling rates, and for closely spaced dots, which is in line with the requirements for the charge quadrupole qubit. It is also scalable in a one-dimensional array, allowing for multi-qubit devices in the near future. Additionally, we present charge sensing measurements of quantum dots using fast cryogenic amplification.