What's the best type of qubit?
Even Google doesn't know....
Google recently announced that it is diversifying its quantum computing efforts to look at neutral atom systems as well as superconducting qubits. What does this mean?
One of the most hotly debated topics in quantum computing is “what is the best type of qubit?” - the fundamental hardware that makes up the basic building blocks of a quantum computer. Current research and development is spread across a range of ideas - as well as superconducting circuits and neutral atoms, ideas such as silicon spins, trapped ions and photons are all attracting attention - and funding.
My own view is that, over the short term (which could be 5-10 years), different approaches will become popular and find their own use cases, much as technologies such as vacuum tubes and germanium did in the development of digital computers. Some will turn out like Charles Babbage’s Difference Engine - clever ideas that aren’t practical engineering concepts. But in the long term (maybe 20+ years) one form will become dominant due to efficiency and economies of scale - the equivalent of the silicon transistor. The thing is that right now I don’t believe anyone can foresee which type of hardware will win out in the long run.
The main story of the last few years has been superconducting qubits. The 2025 Nobel Prize for physics went to the pioneers of the technology behind such systems, in particular showing that they could demonstrate quantum behaviour at a larger scale than single atoms, making it easier to fabricate stable qubits. High-bandwidth control wiring allows these systems to operate at impressive gate speeds, helping them win the early rounds of the "qubit count" wars, with the first systems that reached hundreds of qubits.
Over the last couple of years, Google and IBM’s marketing departments have helped to drive plenty of headlines about superconducting qubits. It probably doesn’t hurt that superconducting quantum computers are quite photogenic at current scales - giving the recognisable chandelier structure. My own view has been, as ever, sceptical - “quantum advantage” appears to be for contrived problems of no economic value, while the “exponential error correction” at this stage merely means that error correction can make things better rather than worse.
However, it has been suggested that superconducting qubits face major scaling constraints to go from several hundred to several thousand qubits. Challenges include the physical density of control wiring required to go to larger systems, as well as the thermal load challenges of scaling up those pretty chandeliers to cool tens of thousands of superconducting qubits. In this context, it is notable that Google has decided to diversify their approach (even though they claim to still be “confident that commercially relevant quantum computers based on superconducting technology will become available by the end of this decade”).
Neutral atom systems work in a very different way, using “optical tweezers” to move individual atoms together. This reduces the amount of wiring needed and provides a lot of flexibility - however, it is as clunky as it sounds, needing to physically move qubits to make them interact and run gate operations. This means they tend to run a lot slower than superconducting circuits.
Of course, neutral atoms are no panacea for scaling challenges. All the suggested types of qubits face scaling challenges. The roadmaps all rely on various fundamental innovations and breakthroughs at various scales - both scientific and engineering challenges to be overcome.
Google may have chosen neutral atoms as the second string to their bow, but there are plenty of other options out there as well. Here in Australia we have two companies, Diraq and Silicon Quantum Computing, building qubits out of silicon, and another one, Quantum Brilliance, using defects in diamond crystal. Notably, in recent months the government has invested reasonable amounts (around $15-20m each) into all three companies, alongside its “big bet” of a $1bn investment in the US company PsiQuantum and its “photonic qubit” technology. Meanwhile other companies such as IonQ are developing trapped ions, and Microsoft is still trying to make “topological qubits”.
This variety of options reinforces my assertion that no-one knows what the best hardware will be. For investors, you probably want to take a portfolio approach of spreading your bets across different options, or maybe looking at companies that provide higher layers of the stack such as control systems, operating systems or algorithms. Similarly, companies looking to trial quantum computing solutions and build up expertise should be wary of approaches that tie them into one particular type of hardware.
Google drove the headlines about the ‘triumphs’ of superconducting qubits—but now it is clear it is not confident this will be the long term winner. The message is clear: if one of the companies with the deepest pockets in the race is hedging its bets, everyone else probably should be too.
MDR Quantum helps organisations to develop and implement strategies to be ready for the quantum future. If you’re looking for help in planning pilot projects, evaluating suppliers or due diligence on investment opportunities, feel free to get in touch.