An Australian research team has experimentally realised a crucial combination of these capabilities on a silicon chip, bringing the realisation of a universal quantum computer a step closer to being achieved.
They have demonstrated an integrated silicon qubit platform that combines both single-spin addressability - the ability to 'write' information on a single spin qubit without disturbing its neighbours - and a qubit 'read-out' process that will be vital for quantum error correction.
Crucially, the integrated design can be manufactured using well-established technology used in the existing computer industry.
The team is led by Scientia Professor Andrew Dzurak of the University of New South Wales in Sydney, a program leader at the Centre of Excellence for Quantum Computation and Communication Technology (CQC2T) and Director of the NSW node of the Australian National Fabrication Facility.
Last year, the team published a design for a chip architecture that could allow quantum calculations to be performed using silicon CMOS (complementary metal-oxide-semiconductor) components - the basis of all modern computer chips.
In their new study, the team combine two fundamental quantum techniques for the first time, confirming the promise of their approach.
Dzurak's team had also previously shown that an integrated silicon qubit platform can operate with single-spin addressability - the ability to rotate a single spin without disturbing its neighbours.
They have now shown that they can combine this with a special type of quantum readout process known as Pauli spin blockade, a key requirement for quantum error correcting codes that will be necessary to ensure accuracy in large spin-based quantum computers. This new combination of qubit readout and control techniques is a central feature of their quantum chip design.
"We've demonstrated the ability to do Pauli spin readout in our silicon qubit device but, for the first time, we've also combined it with spin resonance to control the spin," says Dzurak.
"This is an important milestone for us on the path to performing quantum error correction with spin qubits, which is essential for any universal quantum computer."
"Quantum error correction is a key requirement in creating large-scale useful quantum computing because all qubits are fragile, and you need to correct for errors as they crop up," says lead author, Michael Fogarty, who performed the experiments as part of his PhD research with Professor Dzurak at UNSW.
"But this creates significant overhead in the number of physical qubits you need in order to make the system work," notes Fogarty.
Dzurak says, "By using silicon CMOS technology we have the ideal platform to scale to the millions of qubits we will need, and our recent results provide us with the tools to achieve spin qubit error-correction in the near future."
"It's another confirmation that we're on the right track. And it also shows that the architecture we've developed at UNSW has, so far, shown no roadblocks to the development of a working quantum computer chip."
"And, what's more, one that can be manufactured using well-established industry processes and components."
Authors of the paper, published in Nature Communications, are UNSW researchers Kok Wai Chan, Bas Hensen, Wister Huang, Tuomo Tanttu, Henry Yang, Arne Laucht, Fay Hudson and Andrea Morello, as well as Menno Veldhorst of QuTech and TU Delft, Thaddeus Ladd of HRL Laboratories and Kohei Itoh of Japan's Keio University.
