Artificial atoms make the stable qubits for quantum calculations, Quantum engineers at UNSW Sydney have created artificial atoms in silicon chips that offer increased stability for quantum computing.

Researchers at UNSW’s quantum calculations illustrate how they created artificial atoms in silicon “quantum dots,” a small space in the quantum chain where electrons are used as cubes (or quantum bits), the basic unit of quantum information.

The idea of making artificial atoms with electrons is not new. Initially theoretically proposed in the 1930s and then experimentally demonstrated in the 1990s, but not in silicon. In 2013 we made an imperfect version of silicon for the first time. Artificial atoms make the stable qubits for quantum calculations.

However, what we really like in our recent research is that artificial atoms with more electrons are healthier cubes than previously thought, which means that they can be used reliably for quantum computing.

This is important because qubits based on only one electron can be very unreliable.

Professor Dzurak compared various types of artificial atoms made by his team with a kind of quantum bit periodic table which he believed was appropriate since 2019, when this pioneering work was carried out, was the International Year of the Periodic Table.

When you return to high school class, you might remember a dust card on the wall that listed all known items in numerical order, starting with hydrogen with one electron, helium with two. Lithium with three etc.

You can even remember that each atom, with increasing weight, regulates itself with more and more electrons in different orbits called “shells”.

It turns out that artificial atoms in our quantum chain also have well-organized and predictable electron shells, just like natural atoms in the periodic table. Artificial atoms make the stable qubits for quantum calculations.

Professor Dzurak and his team at the UNSW School of Electrical Engineering, including PhD student Ross Leon, who is also the lead author of this study, and Dr. Andre Saraiva configures a quantum device in silicon to test the stability of electrons in an artificial atom.

They applied voltage to silicon through closed “electrodes” made of metal electrodes to attract replacement electrons from silicon and form quantum dots, a very small space with a diameter of only about 10 nanometers.

In a true atom you have a positive charge in the middle, like a nucleus, and then the negatively charged electron is held in a three-dimensional orbit around it.

In our case, not a positive nucleus, the positive charge comes from a closed electrode that is separated from silicon by an insulating barrier made of silicon oxide, and then electrons hang underneath, each rotating around the center of the quantum point.

Until now, imperfections in silicon devices at the atomic level had disrupted the behavior of qubits, which resulted in unreliable operations and errors.

However, it appears that extra electrons in the inner skin act as “primers” on the surface of imperfect quantum dots, smoothing objects and providing electron stability in the outer shell.

Achieving electron stability and control is an important step to making silicon-based quantum computers a reality. When a classical computer uses “bits” of information represented by 0 or 1, the cube can store values 0 and 1 on the quantum computer simultaneously. This allows quantum computers to do calculations in parallel rather than one at a time, as conventional computers do. Now the artificial atoms make the stable qubits for quantum calculations.

Then the ability to process data on a quantum computer increases exponentially with the number of qubits it has. Spin is a quantum mechanical property.

The electron acts like a small magnet, and depending on how it rotates the north pole, it can point 1 or 0 up or down.

When electrons form complete shells, either in real atoms or in our artificial atoms, they align their poles in the opposite direction so that the entire rotation of the system is zero, making them useless as qubits.

However, when we add another electron to start a new skin, the extra electron has a rotation that we can now use as cubic again.

This is very important because we can now work with cubes that are far more volatile. Electrons are very fragile. Artificial atoms with 5 or 13 electrons are much healthier.

In the course of recent breakthroughs, the group will explore how the rules of chemical bonds are applied to these new artificial atoms to create “artificial molecules”.

They are used to make better multi-cubic logic gates needed to implement large-scale silicon quantum computers.