Australian scientists have created the world’s first-ever quantum computer circuit – a circuit that contains all the essential components found on a classic computer chip, but on a quantum scale.
The historical discovery, published in Nature today, was nine years in the making.
“This is the most exciting discovery of my career,” senior author and quantum physicist Michelle Simmons, founder of Silicon Quantum computers and director of the Center of Excellence for Quantum Computation and Communication Technology at UNSW at ScienceAlert.
Simmons and her team not only created what is essentially a functional quantum processor, they also successfully tested it by modeling a small molecule in which each atom has multiple quantum states — something a traditional computer would be difficult to achieve.
This suggests that we are now one step closer to finally using quantum processing power to understand more about the world around us, even on the smallest scale.
“In the fifties Richard Feynman said we’ll never understand how the world works — how nature works — unless we can actually start on the same scale,” Simmons told ScienceAlert.
“If we can start to understand materials at that level, we can design things that have never been made before.
“The question is: how do you actually control nature at that level?”
The latest invention follows the creation of the team’s first ever quantum transistor in 2012.
(A transistor is a small device that controls electronic signals and is just one part of a computer circuit. An integrated circuit is more complex because it brings together many transistors.)
To make this leap in quantum computing, the researchers used a scanning tunneling microscope in an 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 how electrons jump along a series of single- and double-bonded carbon atoms in a polyacetylene molecule.
The trickiest parts were figuring out exactly how many atoms of phosphorus there should be in each quantum dot; exactly how far apart each dot should be; and then developing a machine that could place the tiny dots in exactly the right place in the silicon chip.
If the quantum dots are too large, the interaction between two dots becomes “too large to control them independently,” the researchers say.
If the dots are too small, it introduces randomness because each additional phosphorus atom can significantly change the amount of energy needed to add another electron to the dot.
The final quantum chip contained 10 quantum dots, each consisting of a small number of phosphorus atoms.
Carbon double bonds were simulated by placing less distance between the quantum dots than carbon single bonds.
Polyacetylene was chosen because it is a well-known model and could therefore be used to prove that the computer correctly mimicked the movement of electrons through the molecule.
Quantum computers are necessary because classical computers cannot model large molecules; they are just too complicated.
For example, to make a simulation of the 41-atom penicillin molecule, a classical computer would use 10 . need86 transistors, that is “more transistors than atoms in the observable universe†
For a quantum computer, it would only need a processor with: 286 qubits (quantum bits).
Because scientists currently have limited insight into how molecules function on an atomic scale, there is a lot of guesswork involved in creating new materials.
“One of the holy grails has always made a high temperature superconductor‘ says Simmons. “People just don’t know how it works.”
Another possible application for quantum computing is the study of artificial photosynthesis, and how light is converted into chemical energy through an organic chain of reactions.
Another big problem that quantum computers can help solve is making fertilizers. Triple nitrogen bonds are currently broken under high temperature and pressure conditions in the presence of an iron catalyst to create solid nitrogen for fertilizer.
Finding another catalyst that can make fertilizer more effective can save a lot of money and energy.
Simmons says achieving the move from quantum transistor to circuit in just nine years mimics the roadmap laid out by the inventors of classical computers.
The first classical computer transistor was made in 1947. The first integrated circuit was built in 1958. Those two inventions were 11 years apart; Simmons’ team made that jump two years ahead of schedule.
This article was published in Nature†