A group of scientists led by the 2018 Australian Professor of the Year, Michelle Simmons, achieved the first two qubits gate between atomic atoms in silicon, an important milestone in the search for the team to build a quantum computer at an atomic scale. The fundamental piece of research was published today in the journal Nature.
A two-qubits gate is the central building block of any quantum computer, and the UNSW equipment version is the fastest shown in silicon, completing an operation in 0.8 nanoseconds, which is ~ 200 times faster than other existing tours based on doors of two qubits.
In Simmons' group approach, a two-qubits gate is an operation between two turns of electrons, comparable to the role that classical logic gates play in conventional electronics. For the first time, the team was able to build a two-qubits gate by placing two qubits of atoms closer together than ever before, and then, in real time, observing and measuring in a controlled manner their states of rotation.
The unique approach of the equipment for quantum computing requires not only the placement of the qubits of individual atoms in the silicon, but also all the associated circuits to initialize, control and read the qubits in the nanoscale, a concept that requires such exquisite precision that was thought for a long time. Be impossible but with this important milestone, the team is now positioned to translate its technology into scalable processors.
Professor Simmons, director of the Center for Excellence for Quantum Computing and Communication Technology (CQC2T) and founder of Silicon Quantum Computing Pty Ltd., says that the last decade of previous results perfectly set the team to change the limits of what is believes that it is "humanly possible".
"The Atom qubits hold the world record for the longest coherence times of one qubit in silicon with the highest fidelities," she says. "By using our unique manufacturing technologies, we have already demonstrated the ability to read and initialize single electron spins in qubits of silicon atoms with very high accuracy. We have also shown that our atomic scale circuits have the lowest electrical noise of all systems so far, designed to connect to a qubit semiconductor.
"The optimization of all aspects of the design of the device with atomic precision has now allowed us to build a really fast and highly accurate two qubits gate, which is the fundamental component of a silicon-based scalable quantum computer.
"We have really shown that it is possible to control the world on an atomic scale, and that the benefits of the approach are transformative, including the remarkable speed at which our system operates."
The Dean of Science at UNSW, Professor Emma Johnston AO, says that this key document shows even more how innovative Professor Simmons' research is.
"This was one of the final milestones of Michelle's team to demonstrate that they can really make a quantum computer with atomic qubits. Their next main objective is to build a quantum integrated circuit of 10 qubits, and we hope they reach it in 3-4 years".
Get up and approach with qubits: engineering with an accuracy of only one billionth of a meter.
Using a tunneling microscope to precisely position and encapsulate phosphorus atoms in silicon, the team first had to calculate the optimal distance between two qubits to allow the crucial operation.
"Our manufacturing technique allows us to place the qubits exactly where we want them. This allows us to design our two qubits gate to be as fast as possible," says study co-author Sam Gorman of CQC2T.
"We have not only approached the qubits since our last advance, but we have learned to control all aspects of device design with sub-nanometer accuracy to maintain high fidelity."
Observing and controlling qubit interactions in real time.
The team was able to measure how qubits states evolved in real time. And, what is more exciting, the researchers showed how to control the interaction force between two electrons on the nano-second time scale.
"It is important to note that we were able to move the qubit electrons closer or farther, activating and deactivating the interaction between them, a prerequisite for a quantum gate," says another co-author, Yu He.
By: Preeti Narula