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    Just Announced: The First-Ever Quantum Circuit

    Australian scientists have developed the world’s first quantum computer circuit, containing all the essential components found on a classic computer chip, but on a quantum scale.

    The groundbreaking discovery, published today in Nature, took nine years to complete. This is the most exciting discovery of my career, senior 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, said. Not only did Simmons and her team create 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 conventional computer would struggle to achieve. This suggests that we are now one step closer to the quantum processing power to understand more about the world around us, even at the smallest scale.

    In the 1950s, Richard Feynman said that if we couldn’t actually start making it on the same scale, we’d never understand how the world works, how nature works, Simmons said. If we can start understanding 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 development 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 ties many transistors together.) Um To make this leap in quantum computing, the researchers used a scanning tunneling microscope in an ultra-high vacuum to place quantum dots with subnanometer precision.

    The placement of each quantum dot had to be just right for the circuit to mimic how electrons hop along a chain of single- and double-bonded carbons in a polyacetylene molecule.

    The hardest parts were figuring out: exactly how many phosphorus atoms should be in each quantum dot; exactly how far apart each point should be; and then to develop a machine that could place the tiny dots in just the right arrangement in the silicon chip. If the quantum dots are too large, the interaction between two dots becomes too large to control independently, the researchers say. If the dots are too small then it introduces randomness as 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 composed of a small number of phosphorus atoms. Double carbon bonds were simulated by setting a smaller distance between the quantum dots than single carbon bonds. Polyacetylene was chosen because it is a known model and could therefore 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 just too complex. For example, to create a simulation of the penicillin molecule with 41 atoms, a classical computer would need 1086 transistors, which is more transistors than there are atoms in the observable universe. A quantum computer would only need a processor with 286 qubits (quantum bits).

    Because scientists currently have limited insight into how molecules work at the atomic level, a lot of guesswork has to be made when designing new materials. Making a high-temperature superconductor has always been one of the holy grails, says Simmons. People just don’t know how it works. Another potential application for quantum computing is to study artificial photosynthesis and the conversion of light into chemical energy through an organic reaction chain.

    Another big problem that quantum computers could solve is the production of fertilizers. Triple nitrogen bonds are currently broken under high temperature and pressure conditions in the presence of an iron catalyst to produce solid nitrogen for fertilizers. Finding another catalyst that can make fertilizers more effective could save a lot of money and energy. Simmons says the achievement of going from quantum transistor to integrated circuit in just nine years mimics the roadmap laid out by the inventors of classical computers. The first classic computer transistor was developed in 1947. The first integrated circuit was built in 1958. These two inventions were 11 years apart; The Simmons team made this leap two years ahead of schedule.

    This article was published as well by ScienceAlert & Nature

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