Meet the quantum tribes: Six competing visions of fault-tolerant computing The quest for fault-tolerant quantum computing is taking many paths For a technology that's apparently poised for a commercial breakthrough, quantum computing research is still pursuing a surprising number of approaches to creating a scalable, fault-tolerant quantum computer (FTQC). While all of these approaches effectively do the same thing - creating, stabilising and manipulating qubits (the basic units of quantum computing information) in order to perform calculations on them, the nature of both the qubits and the underlying hardware vary widely. Unlike classical computing, which quickly converged on silicon CMOS as the prevailing architecture, quantum computing remains divided among several competing camps. Each purport to be a viable route to fault tolerance, and proponents of each point to different strengths in speed, fidelity, connectivity, scalability or manufacturability. The fact that so many approaches remain in contention speaks both to the decades-long development timescales and the immense challenges that remain to create a commercially viable, fault-tolerant and scalable device. It also raises the question of whether the arrival of a FTQC is really as imminent as some in the industry suggest. "When we started Phasecraft, I thought that there would be a few hardware companies and many algorithms or software companies, but it's the opposite that turned out to be true," Ashley Montanaro, co-founder and CEO of quantum algorithm startup Phasecraft, told Computing at the Economist's Commercialising Quantum Global event last month. So what are the main approaches - or modalities as they are known? What are the pros and cons of each? And will a multiplicity of approaches continue to exist or will one eventually conquer all? Efforts to narrow the field are under way through initiatives such as DARPA's Quantum Benchmarking Initiative in the US and the UK's ProQure