UNSW unlocks qubit signal frequency control in quantum advancement

A team of researchers from the university have successfully 'tuned' precision atom qubits in a similar way to tuning in to different radio stations.
Written by Asha Barbaschow, Contributor

Researchers from the University of New South Wales (UNSW) have announced a new milestone in their pursuit of creating a quantum computer chip in silicon.

The scientists from the Centre of Excellence for Quantum Computation and Communication Technology (CQC2T) based out of the university have demonstrated the ability to tune the control frequency of a quantum bit (qubit) by engineering its atomic configuration.

Working alongside experts at Indiana-based Purdue University, the researchers built two qubits; the first was an engineered molecule consisting of two phosphorus atoms with a single electron, and the other a single phosphorus atom with a single electron. UNSW said the two qubits were then placed 16 nanometres apart in a silicon chip.

"By patterning a microwave antenna above the qubits with precision alignment, the qubits were exposed to frequencies of around 40GHz," the university explained. "The results showed that when changing the frequency of the signal used to control the electron spin, the single atom had a dramatically different control frequency compared to the electron spin in the molecule of two phosphorus atoms."

UNSW explained that creating engineered phosphorus molecules with different separations between the atoms within the molecule allows for families of qubits with different control frequencies. It said as a result, each molecule can be operated individually by selecting the frequency that controls its electron spin.

"Individually addressing each qubit when they are so close is challenging," 2018 Australian of the year recipient and CQC2T director Professor Michelle Simmons said. "The research confirms the ability to tune neighbouring qubits into resonance without impacting each other."

UNSW Research Fellow Sam Hile said the achievement allows the scientists to "tune" into a molecule in a similar way to tuning in to different radio stations.

According to the university, tuning in and individually controlling qubits within a 2-qubit system is a precursor to demonstrating the entangled states that are necessary for a quantum computer to function and carry out complex calculations.

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"By engineering the atomic placement of the atoms within the qubits in the silicon chip, the molecules can be created with different resonance frequencies. This means that controlling the spin of one qubit will not affect the spin of the neighbouring qubit, leading to fewer errors -- an essential requirement for the development of a full-scale quantum computer," UNSW added.


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