Topological quantum computing: The quest for a quality qubit

Quantum computers will do extraordinary things. They will create extremely complex digital twins at the molecular level and develop optimization solutions at the global level, allowing us to reshape whole industries, from pharmaceuticals to logistics.

But before we can see any of those benefits, we need a viable quantum computer that can solve hypercomplex problems. The quantum computers we have today can solve problems, but nothing an ordinary computer can’t handle. 

To take the next big leap in quantum computing, we need a stable qubit.

A qubit, or quantum bit, is the most fundamental building block of a quantum computer. It functions much like a transistor on a standard computer chip, but it can calculate in ways no traditional microprocessor ever could. Building a useful quantum computer would require entangling thousands of these qubits.
The problem is qubits are inherently unstable. The most infinitesimal shift in temperature, structure, or electromagnetic field can destabilize a qubit, turning any information it contains into useless noise. The life of most qubits today can be measured in mere milliseconds. 

Nokia Bell Labs, however, is researching a new type of qubit that is extremely stable. Called a topological qubit, it is much more resilient to external stimuli, allowing it to remain viable for a period of hours, if not days or weeks. This topological approach to quantum computing could be revolutionary, drastically reducing the size and cost of future quantum computers, as well as the resources necessary to maintain it. 

Nokia Bell Labs has been investigating the basis of topological quantum computing for years, building upon decades of research into condensed matter physics including our Nobel Prize-winning discovery of the fractional quantum Hall effect. We have decided to share our progress and research roadmap as we are nearing a topological-qubit breakthrough. The quantum computing group, led by Principal Researcher Robert Willett, expects to hit several key milestones in 2025, showing the viability of their topological quantum research. And in 2026, the team hopes to demonstrate a stable topological qubit.

"We are building a new type of qubit that is intrinsically stable and easy to control,” Willett said. “This topological qubit will have extremely low error rates, which means we would not need to build massive redundancy into quantum computers. This would make quantum computers smaller, more energy efficient and massively powerful.”

A physics-based approach to scalable quantum computing

While huge strides have been made in quantum computing in the last decade, most of these approaches are based on brute-force engineering. These early quantum computers use the first generation of qubits, which — while of tremendous scientific value — are not suited to the task of building a practical computer. Using this first generation of qubits requires building computing systems that rival the world’s most powerful supercomputers in complexity and size. These brute-force quantum computers require hundreds of thousands of qubits to work as these qubits are constantly losing their stability. 

Nokia Bell Labs, however, is approaching this problem from a completely different standpoint. Instead of attempting to force first-generation qubits to behave in ways they were never intended, Nokia Bell Labs is rethinking the fundamental physics of how quantum computers operate. This approach will produce a topological qubit grounded in Nokia Bell Labs’ research in quantum mechanics and designed to meet the unique requirements of quantum computing.

The science behind the topological qubit is quite complex, to say the least. As its name implies, the topological qubit takes advantage of the mathematical principle of topology. Topology deals with how a geometric object can maintain its properties even as it is stretched and deformed.

A classic example of a topological system is a coffee cup. A coffee cup is a vessel for holding liquid with a handle containing a hole attached to its side. If you were to stretch out or warp the handle and elongate and deform the cylinder, you would have a strange-looking cup, but you still would have preserved the topology of the coffee cup. It is still recognizable as a coffee cup, and it still functions as a coffee cup.

Willett and his team are applying those same topological principles to a quantum computer. They are creating a system that preserves its computing functions even as it is warped and contorted. 

Specifically, Willett’s lab has generated a supercooled electron liquid, which acts as canvas for the quantum computer. By applying electromagnetic fields to parts of that canvas, qubits are “painted” on its surface. Then, using additional electromagnetic fields, the team maneuvers charges around one another on the canvas. This braiding of the charges acts as a switch between topological states in the qubits. The resulting braided structure is extremely stable as the quantum states of qubits are locked in place for days or weeks at a time. 

By moving charges into different positions on the canvas, the computer can manipulate the topological quantum states of its qubits. This intentional manipulation of these states is how a topological quantum computer performs calculations. But all the factors that normally cause instability in a quantum computer – temperature fluctuations, vibration, stray particles – have practically no impact. Even if an errant particle were to knock a single charge out of whack, the topology of the braided structure would prevent the chain reaction of errors that plague most quantum computers today. 

“The topological states of these particles are fundamentally resilient,” Willett said. “It’s very hard to change the background state of the system. You need to perform such a specific maneuver to change a particle’s quantum state, that it becomes extremely difficult for it to change accidentally. That’s where you get the stability of a topological quantum computer.”

The next steps toward a viable topological qubit

Nokia is just one of two companies pursuing a topological qubit, and it is well down the path to proving the technology works. To demonstrate a viable topological qubit, Nokia Bell Labs needs to hit three key milestones, the first of which was achieved by Willett in 2023. In that first milestone, Nokia Bell Labs demonstrated it could maintain a topological quantum state and manipulate a single charge within that quantum state. 

The second milestone, which Nokia Bell Labs expects to reach in the first half of 2025, is called a quantum NOT gate. A NOT gate is the most fundamental operation of computing, involving switching a bit from 0 to a 1. If the topological qubit can perform the quantum equivalent of this operation, then it will have met the most basic criteria defining a quantum computer. 

Some might declare victory at this point, but Nokia Bell Labs believes it must achieve another step to prove the viability of the topological qubit. To fully unlock its full capabilities, a qubit needs to do more than perform NOT gate operations. The third milestone involves Nokia Bell Labs demonstrating it can manipulate charges in different ways to perform additional quantum computing operations. Willett’s team is aiming for the second half of 2025 to clear this bar.

Finally, once all three milestones are cleared, Nokia Bell Labs plans to demonstrate a working topological qubit. Nokia anticipates announcing this achievement in 2026. 

This will be a pivotal point in Nokia Bell Labs’ research, allowing us to move beyond understanding and controlling individual topological qubits to creating actual quantum computing devices that could scale from 10 qubits to 100 thousand qubits or more. This would put Nokia Bell Labs on the path to building a topological quantum computer that can truly tackle hypercomplex problems.

“It’s hard to exaggerate the impact that a topological qubit could have on the nascent quantum computing industry,” said Michael Eggleston, Head of Data and Devices Research at Nokia Bell Labs, a department that includes the quantum computing lab. 

“The topological qubit will give the industry a much more practical and economical option for building quantum computers — we could fit a million qubits on a package the size of a silver dollar,” Eggleston said. “Instead of a quantum computer that takes up an entire building and costs billions of dollars, we could create a topological quantum computer of equivalent power that only costs millions of dollars and would fit into a server rack.”

This is a problem that Nokia Bell Labs is uniquely designed to tackle. Just as the transistor — another pivotal Bell Labs invention — was crucial in leading computing from the analog age to the digital age, the topological qubit may very well be the discovery that leads computing from the digital age to the quantum age.