Paul Benioff (1930-2022) was a US physicist who wrote a paper in 1980 that imagined the feats computing might achieve if it could harness quantum mechanics, where the word quantum refers to the tiniest amount of something needed to interact with something else – it’s basically the world of atoms and sub-atomic particles. Benioff’s imagination gave rise to the phrase ‘quantum computing’, a term that represents how the storage and manipulation of information at the sub-atomic level would usher in computing feats far beyond those of ‘classical’ computers.

Benioff coincidently wrote about a vague concept being outlined by Russian mathematician Yuri Manin (1937-2023) who also in 1980 talked up the promises of quantum computing in his book, Computable and uncomputable. Others such as US physicist Richard Feynman (1918-1988) promoted the wonders of computing grounded in the concept of ‘superposition’ – when matter can be in different states at the same time.

Quantum computing is built on manipulating the superposition of the qubit, the name of its computational unit. Qubits, which are often atoms, electrons or protons, are said to be in the ‘basis states’ of 0 or 1 at the same time when in superposition – whereas a computational unit in classical computing is either 0 or 1. This qubit characteristic, on top of the ability of qubits to engage with qubits that are not physically connected (a characteristic known as entanglement), is what proponents say gives quantum computers the theoretical ability to calculate millions of possibilities in seconds. Such a feat dwarfs the abilities of the transistors powering classical computers.

In 2012, five years after Canadian company D-Wave Quantum Systems claimed to have built the world’s first rudimentary (28-qubit) quantum computer, US physicist John Preskill (born 1953) devised the term ‘quantum supremacy’ to describe how quantum devices one day would make classical computers look archaic.

In 2019, a long-awaited world first was claimed. Nasa and Google asserted they had attained quantum supremacy when something that ‘isn’t terribly useful’ was computed ‘in seconds what would have taken even the largest and most advanced supercomputers thousands of years’. IBM peers immediately rejected this claim as ‘grandiosity’, saying an IBM supercomputer could have done the task in two-and-a-half days.

Amid such disputes, billions of dollars are pouring into quantum research – including almost A$1 billion from Australia’s federal and Queensland governments into one project. The money is backing hopes that quantum-based simulations, searches, encryptions and optimisations will lead to advances in artificial intelligence, communications, encryption, finance, medicine, space exploration, and even traffic flows, to name just some areas. Advocates say, in time, quantum devices will help the world overcome the demise of ‘Moore’s Law’, an observation the number of transistors on an integrated circuit, and therefore the speed and ability of classical computers, doubles every two years.

The rise of quantum computing seems so assured some people air concerns about its drawbacks. The most flagged disadvantage is that quantum computers could crack the encryption that protects classical computers. Another worry is that quantum computing could add to global tensions if one superpower gains an edge – China is prioritising the area. Another challenge is that quantum computers are large machines that require their qubits to be kept at a temperature near absolute zero (minus 273 degrees Celsius). So they won’t be in laptops and mobiles.

The big downer on the hopes for quantum computing, however, is that credible physicists say it’s impossible. This view is best articulated by Mikhail Dyakonov (born 1940), a Russian professor of physics who works at the University of Montpellier in France. Such are his achievements, his name describes marvels such as the spin relaxation mechanism, plasma wave instability and surface waves. He has won prizes for physics in France, Russia and the US.

Dyakonov says the insurmountable hurdle is that ‘the proposed strategy relies on manipulating with high precision an unimaginably huge number of variables’. This is the summary of ‘The case against quantum computing’ Dyakonov made in 2018 in IEEE Spectrum, the magazine of the Institute of Electrical Engineers, which calls itself the world’s largest technical professional organisation for the advancement of technology. Dyakonov reiterated the same argument in his book of 2020, Will we ever have a quantum computer?

Dyakonov explains that while a conventional computer with N bits at any given moment must be in one of its 2N possible states, the state of a quantum computer with N qubits is described by the values of the 2N quantum amplitudes, which are continuous parameters (ones that can take on any value, not just a 0 or a 1). This is where the hoped-for power of the quantum computer comes from, ‘but it is also the reason for its great fragility and vulnerability’, he says in the IEEE Spectrum article.

Experts estimate that between 1,000 and 100,000 qubits are needed for a useful quantum computer, Dyakonov says. But the number of continuous parameters describing the state of such an effective quantum computer at any given moment is at least 10 to the power of 300 (10300). How big is that number, asks Dyakonov? ‘It is much, much greater than the number of sub-atomic particles in the observable universe.’

Then, there are the effects of errors. In classical computers, mistakes happen when transistors are switched off when they are supposed to be on, and vice versa. Error-correction programs within classical computers can override these glitches. ‘Could we ever learn to control the more than 10300 continuously variable parameters defining the quantum state of such a system? My answer is simple. No, never,’ Dyakonov says.

Who might be right? One of the world’s leading physicists or the scientists sweet-talking governments, companies and organisations into giving them billions of dollars for research? The hurdles are such, it’s likely that useful quantum computing will rank alongside level-5 (completely) autonomous driving and superhuman AI as tech delusions.

To be clear, no one questions that practical quantum computing could change the world. Scientists will no doubt achieve (and trumpet) incremental advancements in quantum computing. But it might take a long time to progress quantum computing beyond today’s rudimentary levels where quantum machines are no more powerful than classical supercomputers and can’t do practical things.

When the federal and Queensland governments each earmarked $470 million to help US-based PsiQuantum build a ‘groundbreaking utility-scale fault-tolerant quantum computer’ in Australia, they implicitly reinforced the dreams of Benioff, Manin, Feynman and others about the coming age of quantum supremacy.

Did anyone in Canberra or Brisbane read any Dvakonov?