Technology & Science

Qubit record moves quantum computing forward

A record-smashing experiment in a Canadian physics lab has brought room temperature quantum computers and money that can't be counterfeited one step closer to reality.

Qubit survives record 39 minutes at room temperature

Simon Fraser University physicists Mike Thewalt, left, and Kamyar Saeedi and their research team made qubits from phosphorus atoms embedded in a very pure silicon crystal such as the one held by Thewalt in his lab. (Simon Fraser University)

A Canadian-led team of researchers has created a key component of a quantum computer that can survive at room temperature for a whopping 39 minutes, blowing away previous records of just seconds.

The discovery means it might be possible to store quantum bits of data, known as "qubits," even at room temperature, for a practical length of time. That could bring previously science fiction-type ideas — including money that can't be counterfeited — closer to reality. Quantum money, first proposed decades ago but still impossible to produce, would be protected by qubits that can't be copied due to the laws of quantum physics.

Such ideas have been "really sort of pie in the sky because no one has a qubit that can last long enough," said Mike Thewalt, a physics professor at Simon Fraser University in Burnaby, B.C., who co-authored the paper published Thursday online in the journal Science.

But the results of experiments conducted in his lab show "that yeah, you can store quantum information for times that are much longer than people would have suspected… Half an hour at room temperature is pretty amazing."

Previous room temperature survival records for various kinds of qubits made of solid materials such as silicon have ranged from two to 25 seconds.

Researchers are trying to develop quantum computers because they have the potential for exponentially greater computing power than conventional computers. That is because conventional computers encode data as "bits," each of which is in one of  two possible states, "0" or "1," while quantum computers encode data as "qubits" that can each be in multiple states simultaneously. That would allow them to perform multiple calculations at the same time.

The phenomenon of being in a "0" and "1" state simultaneously, known as "superposition," is possible due to the strange laws of quantum physics that apply only to very small particles such as atoms that are used to create qubits.

No deep freeze required

Besides opening the possibility of storing quantum data, the results of the recent experiment suggest that it may one day be possible to build a practical, silicon-based computer that works at room temperature, said Stephanie Simmons, a physics research fellow at Oxford University, who co-authored the paper.

So far, in most experiments, qubits can only be preserved for any length of time when they are cooled to very cold temperatures — close to absolute zero — requiring bulky, cumbersome cooling equipment.

"Commercially it makes a lot more sense to sell something that you can put on a benchtop," said Simmons, a Canadian who is originally from near Kitchener, Ont.

While people have also studied qubits made from gas or photons, solid materials such as silicon are promising for quantum computers because they could make use of the technology developed for silicon-based conventional computers.

Thewalt, Simmons, Simon Fraser University Ph.D. candidate Kamyar Saeedi and their colleagues created their qubits from phosophorus atoms embedded in a very pure silicon crystal by hitting them with magnetic pulses to induce superposition.

The process to prepare the phosphorus atoms to become qubits and to read the data out from them requires it to be cooled to very cold temperatures and for an electron to be added to each atom.

In previous experiments, the qubits lasted only seconds. But the researchers knew that the extra electrons were what was causing the qubits to fall out of their "superposed" state.

'Better than we could have imagined'

They decided to remove the electrons from the atoms using lasers before turning them into qubits, and then see how long they could make the superposition last.

The results were "better than we could have imagined," Simmons said.

Not only did the qubits last a record amount of time at room temperature, but they lasted three whole hours at very cold temperatures, and even survived being warmed up and then cooled down again.

"This would be unheard of in almost any other system," Simmons said.

Thewalt said the researchers were able to do what hasn't been done before because regular silicon's properties make it an ideal material for maintaining coherence. Other researchers have made their qubits from other materials.

While the experiment in Thewalt's lab involved multiple phosphorus atoms, they were all put into the same state to make measurement easier, making them essentially "10 billion copies of one really, really good qubit," Simmons said.

The next step for the researchers is to scale the system up to multiple qubits in a variety of different states.

Ideally, they also hope someone will find a way to read the data at room temperature so no cooling will be required at all.

Simmons said that is theoretically possible.

"It's an engineering challenge rather than a physics challenge," he said.

However, Thewalt said there is still a lot of work to be done before we see a practical, commercial silicon quantum computer.

"It's not going to be something you can use tomorrow," he added. "It's just a step on the way."


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