Centre updates

Tuning into quantum: scientists unlock signal frequency control of precision atom qubits

CQC2T scientists, led by Prof Michelle Simmons, have achieved a new milestone in their approach to creating a quantum computer chip in silicon, demonstrating the ability to tune the control frequency of a qubit by engineering its atomic configuration.

The team from UNSW Sydney successfully implemented an atomic engineering strategy for individually addressing closely spaced spin qubits in silicon. The scientists created engineered phosphorus molecules with different separations between the atoms within the molecule allowing for families of qubits with different control frequencies. Each molecule could then be operated individually by selecting the frequency that controlled its electron spin.

“The ability to engineer the number of atoms within the qubits provides a way of selectively addressing one qubit from another, resulting in lower error rates even though they are so closely spaced,” says Professor Simmons. “These results highlight the ongoing advantages of atomic qubits in silicon.”

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.

“We can tune into this or that molecule – a bit like tuning in to different radio stations,” says Sam Hile, lead co-author of the paper and Research Fellow at UNSW. “It creates a built-in address which will provide significant benefits for building a silicon quantum computer.”

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CQC2T CI Prof Michael Bremner (UTS) co-authors Nature Physics paper on quantum supremacy

CQC2T CI Prof Michael Bremner (UTS)

CQC2T CI Prof Michael Bremner (UTS) links with Google, NASA, UCSB on Nature Physics paper to try to define when quantum computers will overtake classical computers. The researchers said that quantum computers would need almost 50 qubits to process information exponentially faster than a classical supercomputer.

UTS said the first research marks the first clear attempt to identify a benchmark at which quantum computing will surpass the capability of classical computers - which is known as quantum supremacy.
Chief investigator of the UTS branch of the ARC Centre for Quantum Computation and Communication Technology, Professor Michael Bremner, said the line was difficult to define because the advantages offered by quantum computers can be subtle.

“Some applications can have an exponential quantum speed-up over classical computers, while others receive no benefit at all,” he said.
“Understanding when quantum computers become useful is essential, especially when we are limited to using the noisy intermediate-scale devices that currently exist.

“We attempted to find the frontier between classical and quantum computing. We wanted to find the smallest quantum circuits that can do something that cannot be done at all on a classical computer.”



Feynman inspires new CQC2T Nature Communications paper

UNSW physics researcher Sam Gorman

Director of CQC2T, Scientia Professor Michelle Simmons said her team’s approach to building a quantum computer “from the ground up, atom by atom” is inspired by physicist Richard Feynman who said: ‘what I cannot create, I do not understand’. Centre researchers create their atom qubits by precisely positioning and encapsulating individual phosphorus atoms within a silicon chip. Information is stored on the quantum spin of a single phosphorus electron. Simmons’ team use a scanning probe to directly measure the atom’s wave function to show the exact physical location in the chip. “We are the only group in the world who can actually see where our qubits are,” said Prof Simmons.

In the new paper, the team show they can control the interactions between two of these atom qubits so the quantum spins of their electrons become correlated. Building on two other recent results, these three papers collectively confirm the extremely promising prospects for building multi-qubit systems using Centre atom qubits.

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