Milestone Achieved in Quantum Computing with Gate-Defined Silicon Spin Qubits

The study presents a significant advancement in quantum information processing using silicon spin qubits in gate-defined quantum dots, demonstrating quantum correlations at temperatures ranging from 10 mK to 1.1 K. Researchers from Australia and those from Diraq published the study in Nature Communications. By systematically identifying error sources such as dephasing and exploring potential improvements like enhanced material quality and advanced control techniques, the research lays the groundwork for achieving higher qubit operation fidelities and scalable quantum computing architectures in silicon-based systems.

The experimental setup employs aluminium gate stacks on silicon-28 substrates with low residual 29Si. This configuration minimises decoherence by reducing environmental noise, a critical factor in maintaining qubit integrity. The system operates within a dilution refrigerator, utilising specialised instruments for voltage pulses, microwave control, and cryogenic signal detection via a single-island SET charge sensor equipped with amplifiers. This setup enables precise manipulation and measurement of spin qubits in a low-noise environment.

The research incorporates Gate Set Tomography (GST) to address errors, characterise quantum operations, and identify gate-level inaccuracies. Additionally, Hamiltonian phase corrections are applied to counteract drifts or errors over time, ensuring stable qubit operation despite environmental fluctuations.

A significant challenge identified is dephasing during free precession, where qubits interact with the environment, causing random phase shifts that degrade quantum information. To mitigate this, continuous microwave drives under the SMART protocol are implemented. These drives reduce noise susceptibility and preserve qubit coherence for longer periods.

Future research aims to scale up systems using the SMART protocol, incorporating continuous microwave drives to enhance noise resistance. Integration of CMOS manufacturing techniques is planned to improve scalability and error resilience in larger quantum dot processors. This approach will facilitate complex computational tasks by maintaining high qubit fidelity.

The research plans to demonstrate multi-qubit entanglement through violations of Mermin’s inequality, a test for non-local correlations beyond classical limits. Additionally, implementing quantum teleportation protocols is a key objective, advancing capabilities in quantum communication and computation while addressing qubit fidelity and scalability challenges.