UNSW researchers have demonstrated a number of ways to write quantum information into silicon for greater flexibility. Quantum chip design.

Artistic illustration of the 16 quantum states of the antimony atom, and all the different ways one can climb between them.

Artistic illustration of the 16 quantum states of the antimony atom, and all the different ways one can climb between them. Image credit: UNSW Sydney

Quantum computing engineers at UNSW Sydney have shown that they can encode quantum information – the special data in a quantum computer – within an atom, within a silicon chip, in four unique ways.

This feat could alleviate some of the challenges in running tens of millions of quantum computing units in a few square millimeters of a silicon quantum computer chip.

In a recently published paper Nature Communications Engineers explain how they use sixteen quantum ‘states’ of one. Antimony Atoms to encode quantum information.

Antimony is a heavy atom that can be installed into a silicon chip, replacing one of the existing silicon atoms. It was chosen because its nucleus has eight distinct quantum states, plus an electron with two quantum states, resulting in a total of 8 x 2 = 16 quantum states, all within just one atom. . Reaching the same number of states using simple quantum bits – or qubits, the basic unit of quantum information – would require manufacturing and combining four of them.

Lead author Irene Fernandez de Fuentes says the team, led by Scientia professor Andrea Morillo, drew on more than a decade of work that established different quantum control methods to show that the same All are possible within an atom. The antimony atom was implanted into the chip by colleagues at the University of Melbourne using the Heavy Ion Accelerator facilities at the Australian National University.

“First, we showed that we could control the electrons of antimony with a dual magnetic field, as Progress in 2012 This was the first time a qubit had been demonstrated in silicon,” she says.

“We then showed that we could use a magnetic field to tune the spin of the antimony nucleus. This is a standard magnetic resonance method, as used in MRI machines in hospitals, for example. Third. The method was to manipulate the nucleus of an antimony atom with an electric field. Something that was discovered by a lucky accident in 2020..

And the fourth method was to control both the antimony nucleus and the electron, using an electric field. So-called flip-flop qubitsWhich was demonstrated by this team last year.

“This latest experiment shows that all four of these methods can be used in a single silicon chip using the same architecture.”

The advantage of having four different methods is that each method gives computer engineers and physicists more flexibility when designing future quantum computing chips.

For example, magnetic resonance is faster than electric resonance, but the magnetic field spreads widely through space, so it can also affect neighboring atoms. Electric resonance, although slow, can be applied very locally to select a particular atom without affecting any of its neighbors.

“With this large antimony atom, we have complete flexibility in how we integrate it with the control structure on the silicon chip,” says Professor Morello.

Why it matters

Future quantum computers will have millions, if not billions of qubits working simultaneously to crunch numbers and simulate models in minutes that would take today’s supercomputers hundreds or thousands of years to complete. While some teams around the world have made progress with large numbers of qubits, e.g Google’s 70 qubit model or IBM’s version numbered over 1000.they require very large spaces for their qubits to operate without interfering with each other.

But the approach Professor Morello and colleagues at UNSW have taken is to design quantum computing using technology already in use to build conventional computers. Although progress may be slow in terms of the number of working qubits, the benefit of using silicon would mean being able to fit millions of qubits into a single square millimeter chip.

“We are investing in a technology that is difficult, slow, but for very good reasons, one of them being the sheer density of information that it will be able to handle,” says Professor Morello. .

“Having 25 million atoms in a square millimeter is great, but you have to control them one by one. Having the flexibility to do that with magnetic fields, or electric fields, or any combination of those, the system will give us many options to play with when scaling up.”

Back to the lab

Next, the group will use the large computational space of antimony atoms to perform quantum operations that are much more sophisticated than simple qubits. They plan to encode a ‘logical’ qubit inside an atom – a qubit built on more than two quantum levels, to have enough redundancy to detect and correct errors.

“This is the next frontier for practical, useful quantum computer hardware,” says Professor Morello. “Being able to create error-corrected logical qubits within a single atom would be a tremendous opportunity to expand silicon quantum hardware to the point where it would become commercially useful.”

Source: UNSW