A huge step forward in quantum computing has just been announced: the very first quantum circuit

Australian scientists have created the world’s first quantum computing circuit – a circuit that contains all the essential components found on a classical computer chip but on a quantum scale.

The historic discovery, published in Nature today was nine years in the making.

“This is the most exciting discovery of my career,” lead author and quantum physicist Michelle Simmons, founder of Silicon Quantum Computing and director of the Center of Excellence for Quantum Computation and Communication Technology at UNSW, told ScienceAlert.

Not only did Simmons and his team create what is essentially a working quantum processor, but they also successfully tested it by modeling a small molecule in which each atom has multiple quantum states, which a traditional computer would struggle to achieve.

This suggests that we are now on the verge of finally using quantum processing power to better understand the world around us, even on the smallest scale.

“In the 1950s, Richard Feynman said we’re never going to understand how the world works – how nature works – unless we can actually start to do it on the same scale,” Simmons told ScienceAlert.

“If we can start to understand materials at this level, we can design things that have never been done before.

“The question is: how do you actually control nature at this level?”

The latest invention follows the team’s creation of the first-ever quantum transistor in 2012.

(A transistor is a small device that controls electronic signals and forms only part of a computer circuit. An integrated circuit is more complex because it assembles many transistors.)

To take this leap into quantum computing, the researchers used a scanning tunneling microscope in ultra-high vacuum to place quantum dots with sub-nanometer precision.

The placement of each quantum dot had to be just right so that the circuit could mimic the way electrons jump along a chain of single and double bonded carbons in a polyacetylene molecule.

The trickiest parts were figuring out: exactly how many phosphorus atoms should be in each quantum dot; exactly how far apart each point should be; then design a machine that could place the tiny dots in exactly the right arrangement inside the silicon chip.

If the quantum dots are too large, the interaction between two points becomes “too large to control independently”, say the researchers.

If the dots are too small, it introduces randomness because each additional phosphorus atom can dramatically change the amount of energy needed to add another electron to the dot.

The final quantum chip contained 10 quantum dots, each made up of a small number of phosphorus atoms.

Carbon double bonds were simulated by putting less distance between quantum dots than carbon single bonds.

Polyacetylene was chosen because it is a well-known model and therefore could be used to prove that the computer correctly simulated the movement of electrons through the molecule.

Quantum computers are needed because classical computers cannot model large molecules; they are simply too complex.

For example, to create a simulation of the penicillin molecule with 41 atoms, a typical computer would need 1086 transistors, i.e. “more transistors than there are atoms in the observable universe”.

For a quantum computer, it would only take a 286 qubit (quantum bit) processor.

Because scientists currently have limited visibility into how molecules work at the atomic scale, there is a lot of guesswork involved in creating new materials.

“One of the holy grails has always been to make a high-temperature superconductor,” says Simmons. “People just don’t know the mechanism of how it works.”

Another potential application of quantum computing is the study of artificial photosynthesis and how light is converted into chemical energy by an organic chain of reactions.

Another big problem that quantum computers could help solve is the creation of fertilizers. Nitrogen triple bonds are currently broken under conditions of high temperature and pressure in the presence of an iron catalyst to create fixed nitrogen for fertilizer.

Finding a different catalyst that can make the fertilizer more efficient could save a lot of money and energy.

According to Simmons, the successful transition from quantum transistor to circuitry in just nine years mimics the roadmap laid out by the inventors of classical computers.

The first conventional computer transistor was created in 1947. The first integrated circuit was built in 1958. These two inventions were 11 years apart; Simmons’ team made that leap two years ahead of schedule.

This article was published in Nature.

Sherry J. Basler