Quantum Data Storage in a Single Atom Brings New Computing Era Closer to Reality

In a big step forward, physicists achieved the first-ever demonstration of storing and retrieving quantum data from the nucleus of a solitary atom embedded in silicon.

We’re on the verge of a quantum computing revolution. Entirely new devices will replace tiny transistors on silicon chips with atomic-scale processors capable of executing exponentially more calculations per second than today’s biggest and fastest supercomputers. The first likely application of such machines would be to accurately model nature at the atomic level. This could lead to life-saving drug design and entirely new ways of harnessing the power of chemistry.

After that, the possibilities seem endless.

While teams around the world are racing to build the first large-scale prototypes of a quantum computer, including the top minds at Google and Microsoft, engineers at the University of New South Wales in Australia are tackling a related challenge: quantum memory. In late March, the researchers published the first-ever demonstration of storing and retrieving quantum data from the nucleus of a solitary atom embedded in silicon.

Quantum physicist Andrea Morello leads the team at UNSW, which has taken a novel approach to building a quantum computer using a single atom of phosphorus. Quantum computers are powered by atomic-scale nodes called quantum bits, or “qubits.” Morello’s team built a proof-of-concept quantum computer where the system’s two qubits are the nucleus and a single orbiting electron of the phosphorus atom.

In his lab, using a powerful magnetic field at temperatures close to absolute zero, Morello can program the nucleus and electron qubits to act like transistors on steroids. A normal transistor can only be programmed to be on or off, a one or a zero. But qubits obey the odd laws of quantum physics, which allow them to register both a one and a zero at the same time, which is called superpositioning. Even better, two qubits can become “entangled,” exponentially multiplying the number of possible states they can occupy at once.

"Quantum computing is a truly transformational technology."

In Morello’s single-atom quantum computer, the state or position of a qubit is called its “spin.” Instead of one and zero, the options are “spin up” and “spin down.” Morello can actually nudge the phosphorus nucleus or electron into either position using finely tuned pulses of microwaves.

In this latest memory experiment, Morello and his colleagues were able to transfer information about the spin position of the electron and store that data temporarily in the nucleus for an impressive 80 milliseconds before transferring it back to the electron — quantum memory in action.

“In a classical computer, if you need to store information to process later — you can take the data from your CPU and copy it in your RAM or hard drive and fish it back up later,” Morello told Seeker. “You can’t do this in quantum mechanics.”

That’s because of the “no-cloning theorem,” which states that you can never make a copy of quantum information. Instead, you must transfer it from one particle to another, essentially erasing the original. Morello’s demonstration proved that it can be done. This first round of experiments only had an 81 percent success rate, but the team is continuing to refine the process.

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Why is memory an important component of the coming quantum computing revolution? Technically, memory isn’t required to run quantum algorithms in a closed system, and the first large-scale quantum computers may not include any memory capabilities.

But things get trickier if you want to create a quantum network of multiple machines in different locations. You could link quantum computers through the conventional internet, but then you would lose the quantum advantage, namely the incredible speed and virtually unhackable security afforded by the quantum phenomenon of entanglement.

“Having quantum computers connected quantum mechanically is one of the holy grails of our field,” said Morello. To create such a quantum network, information would be sent from machine to machine via photons traveling at the speed of light. When a photon arrives, the computer would need to store the new data temporarily before the qubits process it. That’s where quantum memory comes in.

The next step for Morello and his team is to demonstrate the full chain of quantum networking and storage — photon to electron to nucleus and back again. The recent paper was just a “first embryonic demonstration of nuclear quantum memory,” said Morello, not that it was a piece of cake. His team at UNSW is the only group of quantum physicists in the world that has successfully built silicon quantum devices out of notoriously sensitive subatomic particles.

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How far away are we from the first truly large-scale quantum computer? The largest current machine has 10 qubits. The goal is to build a system running on a million qubits. Scalability is paramount, and that’s where Morello believes his method has the greatest advantage. His single-atom system runs on silicon, the same semiconducting material used by the trillion-dollar microchip industry, which can already squeeze a billion transistors onto a $50 chip.

“Our goal over the next five years is to demonstrate a 10-qubit quantum computer that has all the functionality you need for a universal quantum computer,” Morello said. “The idea is that if we manage to demonstrate all the basic functionalities of quantum bits in silicon at atomic scale, then it should be possible to use the highly controlled, highly reproducible, and highly manufacturable technologies of the silicon microchip industry to scale that up to millions of qubits.”

The potential impact of such a large-scale computer is impossible to predict, not only because we’ve never had a chance to test it, but because we still need to develop the quantum algorithms and quantum software to run these exponentially more powerful machines. One of Morello’s initiatives at UNSW is to develop a quantum engineering curriculum to train future quantum programmers.

“Quantum computing is a truly transformational technology,” Morello said. “It’s not just a faster car or a better airplane. It’s a different object that’s never existed before, and we’re only starting to grasp the power and the capabilities of it.”

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