Process boost for quantum processor chips
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Rigetti Computing in the US has developed a new fabrication process to tune its quantum processor chips.
The Alternating-Bias Assisted Annealing (ABAA) technique developed by Rigetti allows for more precise tuning of the qubit frequency of a quantum processor to improve execution of 2-qubit gates and reduce defects, which both contribute to higher fidelity.
This is now being used to fabricate quantum processor chips for Rigetti systems, including the Novera QPU and the upcoming Ankaa-3 quantum computer with 84 qubits that is on schedule for the end of 2024. IT is already shipping a 24 qubit machine to the UK.
Rigetti’s superconducting qubits use Josephson Junctions (JJs), which are two thin layers of superconducting aluminium separated by a barrier of aluminium oxide. Electrons are able to tunnel across the insulator from one electrode to another — resulting in a characteristic frequency for the qubit that allows for it to be controlled and measured.
While the reproducibility and energy loss in these junctions has been difficult to control, the simplicity, scalability, and ease of fabrication of these superconducting devices makes them desirable platforms for building quantum computers.
By applying a series of low, alternating voltages at room temperature to the oxide barrier, the qubit frequencies can be precisely targeted. The ability to tune qubits prior to a chip being packaged is essential for large-scale QPU production, improving the addressability of the qubits, speeds up interactions, and improves the scalability of the technology.
Rather than laser trimming of the chip, the ABAA technique is a simple and scalable process that only requires sending pulses of voltage to the quantum processor chip and was developed in the Rigetti Fab-1 in Fremont, California.
“We’ve long known that having our own foundry is a tremendous asset to our chip design and fabrication processes. Introducing the ABAA technique is a perfect example of our ability to rapidly test and implement new methods to improve our capabilities,” says Dr. Subodh Kulkarni, CEO of Rigetti. “We believe this new technique strengthens our path to scaling to even higher qubit count systems with greater control over our qubit performance.”
The technique also helps to heal some of the defects and imperfections in the Josephson junctions in the quantum processor chips, allowing for clearer communication between qubits and couplers, which also leads to improved performance due to less interference on the circuit.
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