The U.S. Department of Energy (DOE) announced this week that it has named 76 scientists from across the country, including assistant professor of physics Chen Wang, to receive “significant funding for research” with its Early Career Award. It provides university-based researchers with at least $150,000 per year in research support for five years.
DOE Under Secretary for Science Paul Dabbar says DOE “is proud to support funding that will sustain America’s scientific workforce and create opportunities for our researchers to remain competitive on the world stage. By bolstering our commitment to the scientific community, we invest into our nation’s next generation of innovators.”
Wang says, “I feel very honored to receive this award. This is a great opportunity to explore a new paradigm of reducing error for emerging quantum technologies.”
His project involves enhancing quantum bit (qubit) performance using a counter-intuitive new approach. He will harness friction – usually an unwelcome source of error in quantum devices – to make qubits perform with fewer errors. The work is most relevant for quantum computing, he says, but potential applications include also cryptography, communications and simulations.
One of the basic differences between classical and quantum computing – which is not in practical use yet – is that classical computers perform calculations and store data using stable bits labeled as zero or one that never unintendently change. Accidental change would introduce error.
By contrast, in quantum computing, qubits can flip from zero to one or anywhere between. This is a source of their great promise to vastly expand quantum computers’ ability to perform calculations and store data, but it also introduces errors, Wang explains.
“The world is intrinsically quantum,” he says, “so using a classical computer to make predictions at the quantum level about the properties of anything composed of more than a few dozens of atoms is limited. Quantum computing increases the ability to process information exponentially. With every extra qubit you add, the amount of information you can process doubles.”
“Think of the state of a bit or a qubit as a position on a sphere,” he says. “For a classical bit, a zero or one is stable, maybe the north or south pole. But a quantum bit can be anywhere on the surface or be continuously tuned between zero and one.”
To address potential errors, Wang plans to explore a new method to reduce qubit errors by introducing autonomous error correction – the qubit corrects itself. “In quantum computing, correcting errors is substantially harder than in classical computing because you are literally forbidden from reading your bits or making backups,” he says.
“Quantum error correction is a beautiful, surprising and complicated possibility that makes a very exciting experimental challenge. Implementing the physics of quantum error correction is the most fascinating thing I can think of in quantum physics.”
We are already familiar with how friction helps in stabilizing a classical, non-quantum system, he says, such as a swinging pendulum. “The pendulum will eventually stop due to friction – the resistance of air dissipates energy and the pendulum will not randomly go anywhere,” Wang points out.
In much the same way, introducing friction between a qubit and its environment puts a stabilizing force on it. “When it deviates, the environment will give it a kick back in place,” he says. “However, the kick has to be designed in very special ways.” Wang will experiment using a super-cooled superconducting device made of a sapphire chip on which he will deposit a very thin patterned aluminum film.
He says, “It’s a very difficult challenge, because to have one qubit correct its errors, by some estimates you need tens to even thousands of other qubits to help it, and they need to be in communication. But it is worthwhile because with them, we can do things faster and we can do tasks that are impossible with classical computing now.”