Researchers at UNSW Sydney have achieved a significant breakthrough in quantum computing by extending the “coherence time” of spin qubits to two milliseconds—100 times longer than previous benchmarks in the same quantum processor. This extended time allows quantum information to be maintained longer during calculations, which is crucial for performing complex quantum operations.
Coherence time represents how long qubits—the basic units of information in quantum computers—can be manipulated before losing their information. In the quantum world, two milliseconds is extraordinarily long compared to previous standards, enabling more extensive quantum calculations.
The research team previously solved a decades-old technical problem of how to control millions of qubits without generating excessive heat and interference. Instead of using thousands of tiny antennas, they developed a method using just one antenna with a crystal called a dielectric resonator to control all qubits in a chip. This approach addressed the challenges of space, heat, and noise that would increase as more qubits are brought online.
While controlling millions of qubits simultaneously was a breakthrough, the team needed to enable individual manipulation of qubits as well. PhD students Amanda Seedhouse and Ingvild Hansen tackled this challenge through a series of published papers.
The researchers first demonstrated theoretically that continuously rotating qubits—similar to a plate-spinner keeping plates in motion—could improve coherence time to over 230 microseconds. Building on this, they developed the “SMART” qubit protocol (Sinusoidally Modulated, Always Rotating and Tailored).
The SMART protocol manipulates qubits to rock back and forth like metronomes rather than spinning in circles. By applying an electric field to individual qubits, researchers can put them into different tempos from their neighbors while maintaining the same rhythm. This allows individual control of qubits while under global magnetic influence, significantly extending coherence time.
Dr. Henry Yang, a senior researcher on the team, described the SMART protocol as “a simple and elegant way to control all qubits at once that also comes with better performance,” calling it “a potential path for full-scale quantum computers.“
The research team is led by Professor Andrew Dzurak, who is also CEO and founder of Diraq, a UNSW spin-out company developing quantum computer processors that can be manufactured using standard silicon chip techniques.
The team’s next goals include demonstrating the protocol working with two-qubit calculations, then expanding to multiple qubits to prove the theory in practice. These advancements bring us closer to practical quantum computers that could tackle humanity’s significant challenges, including vaccine development, weather system modeling, and climate change prediction.
Reference: I. Hansen, A. E. Seedhouse, K. W. Chan, F. E. Hudson, K. M. Itoh, A. Laucht, A. Saraiva, C. H. Yang, A. S. Dzurak. Implementation of an advanced dressing protocol for global qubit control in silicon. Applied Physics Reviews, 2022; 9 (3): 031409 DOI: 10.1063/5.0096467
