Bell Labs, now at Nokia, zeroes in on photonic quantum computing

Bell Labs invented the transistor, the fundamental building block of all modern electronics, in 1947. In the decades following, it invented Unix, C, the first practical solar cell, the laser, and more. Along the way, it has won ten Nobel prizes and countless other awards.

But what has it done for us lately? Well, with a renewed focus on fundamental research, the lab, which is now part of Nokia, is working to bring the quantum age closer by helping make photonic quantum computing a reality. In September, a team that included Nokia Bell Labs and Princeton, Rutgers, and Rowan universities became one of 15 finalists (among nearly 300 proposals) for the National Science Foundation’s Engines program for their project to advance photonics.

The potential of quantum photonics is that it can allow for quantum computers that operate at room temperature, can be easily manufactured by semiconductor fabs, and can scale without errors. Plus, since they’re already using photons to create the entangled qubits, it would be easier to integrate multiple computers together via quantum networking, which primarily uses entangled photons.

What’s so special about photons?

Unlike superconducting circuits, trapped ions, and annealing computers, which all require cryogenic conditions, photons are naturally resistant to temperature fluctuations and many other environmental factors. That means that qubits made out of photons can operate at room temperature and with lower error rates than other approaches. 

“Magnetic fields can affect an electron, but a photon isn’t affected,” says Tod Sizer, executive vice president and lab leader for optical systems and device research at Nokia Bell Labs. “Heat can affect how fast an electron vibrates — that same notion doesn’t apply to photons. There’s some basic physics about photons that make them more robust to the environment.”

However, to detect the photons, cryogenic temperatures are still required, he says, at least today. The quantum computer itself doesn’t need to be cold, he says. “It’s just to get the answer out, it needs to be cold.”

In addition to keeping their qubits at near-absolute-zero temperatures, companies looking at non-photonic approaches to quantum computers are also working on improving error correction so that they can scale their quantum computers.

“We’d rather not do error correction.” says Sizer. “We’d rather use all the qubits for computing, instead of correcting what we should have gotten right the first time. We’re trying to make very robust systems so we can cascade information from one state to another and not flip.”

That doesn’t necessarily mean that photonic computers won’t need any error correcting codes, he adds. “Just not the massive ones needed in other approaches, and in a perfect world, we wouldn’t need any at all.”

Another benefit to the photonic approach to quantum computing is that the industry already knows how to work with photons. Our communication infrastructure uses photons – typically the regular kind, not the quantum entangled kind – but even entangled photons have been successfully sent over traditional fiber.

Plus, computer chips are already made with wave guides – metal or glass tubes that move photons around. Semiconductor manufacturers fabricate them right into wafers. These wave guides are used to enable faster data transfers inside and between computer components and are particularly useful for high performance computing and AI.

That makes photonic quantum computer manufacturing possible, says Sizer. “The technologies optimized for silicon allow us to create these intricate devices today,” he says.

The lab is working on building its own photonic qubits, says Sizer. “We have, in-house, the quantum optical engineers and the device physicists who can make these devices,” he says. “We made our first hires about four years ago and have been working on it ever since. We’re investing heavily in this space.”

The goal isn’t to make a quantum computer that Nokia can sell, he adds, but about fundamental research that can move the field forward.

But that’s not to say that there aren’t commercial side benefits. For example, some of the work on photonics will allow existing optical networks to carry dramatically more data while using less energy.

“The amount of information in ten years will increase by a factor of up to a hundred,” Sizer says. “So, we need networks that can support a hundred times more information than we do today, and we also have to think about how to make it more cost effective.”

The research the company is doing on quantum detection of photons can be used to send photons over much longer distances than before, for example, and to encode 14 bits of information in every single photon. “Before, we needed 10 photons to send a single bit,” says Sizer. “Now we need to send one photon for 14 bits.”

That would also require significantly less energy compared to any other alternative, says Azimeh Sefidcon, vice president and head of network systems and security research at Nokia Bell Labs, not just for classical networks but for new quantum networks as well. “That would make quantum communication using photons much more scalable and also more cost efficient.”

The photonic quantum work that Nokia Bell Labs is doing is not just marketing hype, says Luca De Matteis, an analyst at Appledore Research. “Not many players have the understanding and expertise that Nokia has in optical networks,” he says. 

Growing quantum competition

Bell Labs isn’t the only organization to recognize the power of photonic computing. In April, the Defense Advanced Research Projects Agency selected a photonic quantum computing company, Xanadu, as one of 15 companies for its Quantum Benchmarking Initiative.

Other companies working on photonic computing include PsiQuantum, ORCA, Quandela, QuiX Quantum, Photonic, Quantum Computing, AEGIQ, Duality Quantum Photonics, Ephos, g2-Zero, Quantum Source, QC82, and QBoson.

In September, PsiQuantum announced that it raised $1 billion in funding. Their goal? a 1-million-qubit photonic computer by the end of 2027.

Also in September, China’s QBoson showed off a 1,000-qubit photonic quantum computer, which is available now to customers via the cloud. The previous month, the company broke ground on a factory dedicated to the mass production of photonic quantum computers. 

According to QBoson, its cloud-based photonic computing platform – previously limited to 550 and 100 qubits – has already processed 68 million computing problems, by over 10,000 developers and more than 900 colleges and universities. The 1,000 qubit threshold allows it to tackle practical problems such as drug molecule design, the company says.

According to Research and Markets, the global photonic quantum computing market is one of the most promising frontiers in quantum technology and is seeing significant growth momentum. In a report released in September, the analyst firm predicted that the photonic quantum computing market will reach $1.1 billion in revenues by 2030 and grow to over $7 billion by 2036.

“I like photonic quantum computing because we have been working with photons for a long time,” says Sridhar Tayur, professor of operations management at Carnegie Mellon University’s Tepper School of Business. “It’s also room temperature and therefore I have a preference for photonics.”

The fact that it can be built using existing semiconductor technology is an added bonus. “We understand the engineering,” he says. “And I understand that it will be much more cost-effective.”

And, since quantum communication involves entangled photons, working with entangled photons in the quantum computer as well will make it more straightforward to network multiple computers together, he adds, compared to networking computers based on semiconducting circuits or trapped ions. “If it’s optical, it’s going to be easier.”

It’s not clear, though, how much of a difference it will make for Nokia Bell Labs to join the photonic quantum computing effort.

“Bell Labs had its heyday in the 1930s to 1970s,” he says. “I was there in 1988 for an internship, and I remember Bell Labs being hallowed ground. The opening welcome was by a Nobel-winning physicist. It had the aura of being at the frontier of human knowledge. I don’t know if the last 25 years had the same kind of shine that was there before.”