Fastest Silicon Two-Qubit Gate Created By UNSW Quantum Physicists

Eddie Gonzales Jr. – MessageToEagle.com – Led by quantum physicist Michelle Simmons of the University of New South Wales (UNSW) in Australia, a group of physicists have built a super-fast version of the central building block of a quantum computer.

They have achieved the first two-qubit gate between atom qubits in silicon – a major milestone on the team’s quest to build an atom-scale quantum computer.

UNSW team. Credit: UNSW Sydney

In their version, a two-qubit gate is the central building block of any quantum computer is the fastest that’s ever been demonstrated in silicon, completing an operation in 0.8 nanoseconds, which is ~200 times faster than other existing spin-based two-qubit gates.

In the Simmons’ group approach, a two-qubit gate is an operation between two electron spins – comparable to the role that classical logic gates play in conventional electronics. For the first time, the team was able to build a two-qubit gate by placing two atom qubits closer together than ever before, and then – in real-time – controllably observing and measuring their spin states.

The team’s unique approach to quantum computing requires not only the placement of individual atom qubits in silicon but all the associated circuitry to initialize, control and read-out the qubits at the nanoscale – a concept that requires such exquisite precision it was long thought to be impossible.

“Atom qubits hold the world record for the longest coherence times of a qubit in silicon with the highest fidelities,” Simmons said in a press release.

“Using our unique fabrication technologies, we have already demonstrated the ability to read and initialize single electron spins on atom qubits in silicon with very high accuracy. We’ve also demonstrated that our atomic-scale circuitry has the lowest electrical noise of any system yet devised to connect to a semiconductor qubit.

“Optimizing every aspect of the device design with atomic precision has now allowed us to build a really fast, highly accurate two-qubit gate, which is the fundamental building block of a scalable, silicon-based quantum computer.

Using a scanning tunneling microscope to precision-place and encapsulate phosphorus atoms in silicon, the team worked out the optimal distance between two qubits to enable the crucial operation, and then  measured how the qubits states evolved in real-time.

The researchers showed how to control the interaction strength between two electrons on the nano-second timescale.

“Importantly, we were able to bring the qubit’s electrons closer or further apart, effectively turning on and off the interaction between them, a prerequisite for a quantum gate,” says other lead co-author Yu He.

“The tight confinement of the qubit’s electrons, unique to our approach, and the inherently low noise in our system enabled us to demonstrate the fastest two qubit gate in silicon to date.

“This was one of Michelle’s team’s final milestones to demonstrate that they can actually make a quantum computer using atom qubits,” UNSW Science Dean, Professor Emma Johnston AO, said.

“Their next major goal is building a 10-qubit quantum integrated circuit – and we hope they reach that within 3-4 years.”

Paper

Written by Eddie Gonzales Jr. – MessageToEagle.com Staff