Rewrite the quantum computer design

Parity Quantum Computing in Innsbruck, Austria, spun off from the University of Innsbruck, Austria in 2020.

In 2013, Wolfgang Lechner had an idea he thought was probably too good to be true: a mathematical trick that would change the way quantum computers encode information. If it worked, he reasoned, it would be a big deal. Quantum computers can, in theory, perform certain calculations many times faster than conventional digital computers, but they are extremely sensitive to interference and difficult to scale. Lechner’s stroke of genius was to give these computers an architecture based on the concept of parity. This could transform them from small laboratory devices into vast commercial machines capable of solving currently unsolvable problems.

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Lechner, a physicist at the University of Innsbruck in Austria, discussed the proposal with a colleague, but they managed to convince themselves that it was a failure. Over the next two years he kept rethinking the idea and says it became an obsession. Finally, at 3am in a hotel room, he had a flash of inspiration that could mean his parity-based approach should work after all.

He quickly filed for a patent and, just six months later, received an intellectual property bid from a major technology company. (Lechner declined to disclose the firm or the size of the offering.) This told him the architecture had commercial potential and he might be better off trying to reap the rewards head-on. So he and his colleagues at the University of Innsbruck decided to turn down the offer and set up a spin-off company. ParityQC launched in 2020 and was named a finalist for The Spinoff Prize 2023.

Three years after its establishment, the company now employs around 30 people. It has won sizable contracts from high-tech manufacturers and governments with a single deal worth several tens of millions of euros. According to Magdalena Hauser, co-CEO of Lechner, this initial success combined with grants from the European Union and the governments of Austria and Germany meant that the company avoided having to garner the backing of venture capitalists. We’ve been making revenue since the beginning, says Hauser.

Overcome the limits

Quantum computers owe their computational ability to certain quantum phenomena of atomic-scale objects. These computers encode data in the form of qubits, which can exist as 0 and 1 simultaneously unlike conventional bits, which exist only as one or the other. Multiple qubits can be entangled to simultaneously generate all possible values ​​from a string of 0s and 1s, allowing for parallel processing that is not possible with classical computers.

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But qubits are fragile. Their states can be disrupted by the slightest amount of heat or other interference. Their lifetime varies according to the type of physical qubit used: ions, neutral atoms, superconducting circuits or quantum dots. They might remain intact for a few seconds if they’re perfectly isolated, or they might disappear after milliseconds if they interact with other qubits during a computation.

A second important problem for quantum computing is the spatial properties of qubits. The physical processes that connect qubits together usually occur only over very short distances, such as the superposition of two electron clouds around atomic nuclei or the connection of two superconducting circuits. This means that each qubit typically only interacts with its closest neighbors, rather than the farthest qubits.

ParityQC’s architecture helps quantum computers cope with both limitations. It does this by changing the way data is encoded in qubits. Rather than representing the values ​​of individual logical qubits as specified by the running program, physical qubits instead record the relationship between pairs of logical qubits in terms of parity. If the qubits in a pair have the same value, then the parity is 1; if the values ​​are different, the parity is 0 (see Project for Quantum Computing).

This change in coding in a parity-based system transforms all operations involving several qubits, no matter how far apart they are, into the equivalent of local interactions. This eliminates the need for long distance interactions. And operations can be performed on all qubits in a computer simultaneously, maximizing the complexity of the calculations that can be performed in the short period during which the qubits remain intact.

A commercial mindset

Ever since I dreamed about parity architecture¹Lechner and his colleagues at ParityQC and the University of Innsbruck have gone on to publish dozens of papers elaborating on the scheme. In one of the most recent²they proposed a specific set of operations, or ports, that rely on parity encoding and confirmed³ that this set would accelerate many of the most important quantum algorithms devised so far. These include an algorithm that would allow quantum computers to find the prime factors of large numbers, posing a threat to internet encryption schemes that rely on the difficulty of such calculations.

To turn this knowledge into revenue, ParityQC licenses its intellectual property to hardware developers so they can build chips that incorporate the architecture. According to Hauser, the company has sold licenses to Japanese electronics giant NEC to produce a superconducting quantum chip and has entered into several consortia set up in response to the German government’s $2 billion ($2.2 billion) investment. to finance the development of quantum technologies.

Notably, the company was jointly awarded an $83 million contract awarded by the German Aerospace Center in Cologne to build ion trap computers. Together with manufacturers eleQtron in Siegen, Germany, and NXP Semiconductors in Eindhoven, the Netherlands, it won the contract to build a 10-qubit demonstration computer and thus develop modular and scalable devices. (This type of computer was also developed by another 2023 Spinoff Prize finalist, Alpine Quantum Technologies, although Alpine is not part of the ParityQC collaboration.)

Sue Sundstrom, a start-up coach based in Clevedon, UK, and judge for The Spinoff Prize 2023, is impressed by what she describes as ParityQC’s analysis of how previously radically different technologies have been able to enter the market and make money. She notes a parallel with Arm in Cambridge, UK, a company that began selling small-instruction-set computer chip designs in the 1980s. She also commends hiring people with commercial experience. For quantum companies that’s pretty rare, she says.

Fellow judge Emily MacKay, who is a technology strategist at Siemens Energy and is based in Cambridge, UK, applauds ParityQC’s efforts to make its architecture scalable and applicable to various types of hardware. Their approach to research is as future-proof as possible, she says. (Your comments on ParityQC do not necessarily reflect the views of Siemens Energy.)

But MacKay adds that the company is faced with an elephant in the room deciding whether to compete or partner with the world’s largest cloud computing provider, Amazon Web Services. Lechner says ParityQC would be an ideal vendor for the larger company, arguing its parity architecture is a good fit for Amazon, which plans to build quantum computers that mitigate errors, partly in hardware and partly through software. We are not in contact [with Amazon] at the moment, but I’d be happy to do so [be]he says.

However, not all specialists are convinced that parity architecture will achieve the desired results, at least when it comes to solving optimization problems (such as maximizing the return on a financial portfolio or minimizing the distance traveled by commercial vehicles). Itay Hen, a numerical physicist at the University of Southern California in Los Angeles, wonders whether a quantum computer equipped with the architecture could solve such problems faster than a classical computer would, given the absence of any quantum algorithm that guarantees such a result. Even if we had the perfect quantum computer, we still wouldn’t know if it’s better than a laptop, he says.

Lechner acknowledges that there is no general proof that quantum computers have an edge over their classical counterparts when it comes to optimization problems. But he is confident that at some point in the next few years, perhaps around 2030, the parity architecture will allow a quantum computer to surpass this milestone for one or more problems, with classically impossible optimization made possible by new algorithms that they emerge. This is our dream, says Lechner, and the goal we are working towards.