Error-correction breakthroughs bring quantum computing a step closer

QuEra eyes magic state distillation

One of Nord Quantique’s competitors – one that already has a quantum computer on the market – is QuEra. It uses neutral atoms instead of superconducting circuits, and it, too, recently announced a breakthrough in error correction. “Some of our experiments took only eight physical qubits to make a logical qubit,” says Yuval Boger, the company’s CMO.

Then, in January, the company released a roadmap about when their new error-corrected computers will be available to the public. According to QuEra, it will offer a commercial quantum computer this year with ten logical qubits using its new error correction mechanism, based on transversal gates. These gates prevent error propagation between qubits, which reduces error rates.

In 2025, it expects to have a new kind of error correction mechanism, magic state distillation, to allow for a quantum computer with 30 logical qubits. Magic state distillation allows for a greater variety of gates, which is a crucial step towards building universal quantum computers instead of today’s special-purpose ones.

And, in 2026, the company expects to release a 100-logical-qubit computer, which will push quantum computers beyond the limits of what classical computers can do.

The downside? QuEra’s computers are slower than the alternatives. “We don’t want to intermingle error correction with speed,” says Boger. “Speed is a different matter, because different technologies run at different speeds.

QuEra has had a quantum computer available on Amazon Braket since November of 2022, he says.

It can take a few months to get a computer from the lab to production, says Boger, so some early customers will be able to get it via the cloud this year. “The waitlist is already open,” he says. It will be available to everyone next year, he adds.

Customers can also order an on-premises version of the computer. “If they place an order today, they can get it in 2025,” he says. “It takes us a year or a year and a half to deliver because they’re made to order.”

These won’t be world-changing computers, he says. “If you want to simulate a quantum circuit of 10 qubits, you could do it on your cell phone.” But early customers will be able to start learning how error correction works, how to write quantum software, and start testing algorithms.

Alice & Bob devise cat qubits

A third quantum computing startup, Alice & Bob, announced their new quantum error correction architecture in January.

Alice & Bob is also using the bouncing photons trick, says CEO Théau Peronnin. “But instead of bounding around a mirrored ball, it’s bouncing around an electronic circuit,” he says. IBM and Google are also experimenting with this, he adds, but they only use single photons.

Alice & Bob, like Nord Quantique, uses multiple photons. It also uses software, namely low density parity check code. IBM is experimenting with this approach in its quantum computers, as are other companies.

But Alice & Bob’s biggest breakthrough in error correction comes from cat qubits –  named after Schroedinger’s Cat – which reduce the number of dimensions that noise comes from.

Normally, says Peronnin, qubits can switch from, say, zero to one –  just like regular bits – when they’re not supposed to. They can also shift phase. Alice & Bob’s cat qubit error correction technique almost completely eliminates the possibility of switching from a zero to a one. “By doing that we’re slightly degrading the performance on phase shift, but only a small amount,” he says.

This reduces the total number of physical qubits required to make one logical qubit by a factor of 200. So, for example, it would take 20 million qubits for Google’s state-of-the-art computer to run the encryption-breaking Shor’s Algorithm, he says. “With us, it would take slightly fewer than 100,000 quantum bits.”

Plus, this approach is faster than what QuEra offers, he adds. “What QuEra has done is absolutely beautiful but, at the end of the day, we’re building a computer,” he says. “And speed matters.”

Alice & Bob doesn’t have a commercially available computer out yet, but it will be up on one of the big three cloud providers in the next couple of months, he says. “Currently, we only serve special clients on-premise,” he says.

Which error correction is best?

The best strategy, says Sam Lucero, chief quantum analyst at Omdia, would be to combine multiple approaches to get the error rates down even further.

For example, with Nord Quantique’s current error-correcting system, instead of needing 1,000 physical qubits for one logical qubit, they might, say, only need 100. “That’s very substantial,” Lucero says.

But adding error-correcting coding can reduce the total physical qubits needed even further, he adds. “There are dozens of these codes,” he says. “This type of code seems to allow for even more reduction in the number of physical qubits needed to make one logical qubit based on the coding efficiency.”

The bigger question is which type of qubit is going to become the standard – if any. “Different types of qubits might be better for different types of computations,” he says.

This is where early testing can come in. High-performance computing centers can already buy quantum computers, and anyone with a cloud account can access one online.

Using quantum computers via a cloud connection is much cheaper and quicker. Plus, it gives enterprises more flexibility, says Lucero. “You can sign on and say, ‘I want to use IonQ’s trapped ions. And, for my next project, I want to use Regetti, and for this other project, I want to use another computer.’”

But stand-alone quantum computers aren’t necessarily the best path forward for the long term, he adds. “If you’ve got a high-performance computing capability, it will have GPUs for one type of computing, quantum processing units for another type of computing, CPUs for another type of computing – and it’s going to be transparent to the end user,” he says. “The system will automatically parcel it out to the appropriate type of processor.”