What is quantum computing and how will it affect you?

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By Jeremy Schultz, Reuters

Google said on Wednesday it had achieved a breakthrough in computer research, by solving a complex problem in minutes with a so-called quantum computer that would take today's most powerful supercomputer thousands of years to crack. Official confirmation of the breakthrough in quantum computing came in a paper published in science journal Nature, after weeks of controversy following the leak of a draft, over whether Google's claim of "quantum supremacy" was valid. Computer scientists have for decades sought to harness the behaviour of sub-atomic particles that can simultaneously exist in different states - in contrast to the "real" world that people perceive around them. REUTERS/Text by Douglas Busvine

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So, whereas traditional computing relies on bits, or ones and zeros, quantum computing uses quantum bits, or qubits, that can be both one and zero at the same time. This property, called superposition, multiplies exponentially as qubits become entangled with each other. The more qubits that can be strung together, the vastly more powerful a quantum computer becomes. But there's a catch: Quantum researchers need to cool the qubits to close to absolute zero to limit vibration - or "noise" - that causes errors to creep into their calculations. It's in this extremely challenging task that the research team at Google, a unit of Alphabet Inc, has made significant progress. CEO Sundar Pichai compared the achievement to building the first rocket to leave the Earth's atmosphere and touch the edge of space, an advance that brought interplanetary travel into the realm of the possible.

RANDOM TASK

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Google developed a microprocessor, named Sycamore, that packs a total of 54 qubits. Measuring about 10 mm across, it is made using aluminium and indium parts sandwiched between two silicon wafers. In their experiment, the researchers were able to get 53 of the qubits - connected to each other in a lattice pattern - to interact in a so-called quantum state. They then set the quantum computer a complex task to detect patterns in a series of seemingly random numbers. It solved the problem in 3 minutes and 20 seconds. They estimated that the same problem would take 10,000 years for a Summit supercomputer - the most powerful in the world today - to solve. "This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy for this specific computational task, heralding a much-anticipated computing paradigm," wrote the research team, led by Google AI's Frank Arute. 

WHAT MAKES QUANTUM COMPUTERS SO POWERFUL?

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Another property of sub-atomic particles is for them to become 'entangled' - meaning that they can influence each other's behaviour in an observable way. Combining entanglement with superposition leads to exponential increases in computing power with each additional qubit. The Sycamore processor designed by Google, a unit of Silicon Valley technology giant Alphabet, had 54 qubits arranged in a two-dimensional grid. In the experiment only 53 could be made to work - still enough to produce a successful result. 

WHY DID IT TAKE SO LONG TO GET HERE?

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Physicists have been talking about quantum computing for over 30 years, but the challenges of making them work are daunting. The qubits need to be cooled to just above absolute zero to reduce 'noise' - or vibration - that introduces errors into the calculations made by a quantum computer. Google's researchers, in solving the problem with a high degree of fidelity - or accuracy - can reasonably claim to have achieved a significant milestone, say physicists.

DOES THIS MEAN THAT OLD COMPUTERS ARE FINISHED?

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Critics, including rival IBM, say Google is hyping its achievement and creating the misleading impression that quantum computers have effectively rendered all conventional computers obsolete. By adding disk storage the Summit supercomputer - which is made by IBM - could have solved Google's random number problem in at most 2-1/2 days, with greater accuracy, they say. Sceptics also argue that Google has only solved a very narrow task, and that quantum computing is still a long way away from practical use. In the real world, quantum computers are likely to work in harness with classical computers, making use of their respective strengths. 

SO WHAT'S NEXT?

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Researchers from the Google AI research team see potential uses for quantum computing in fields such as machine learning, and materials science and chemistry. They admit, though, that still-greater accuracy will be needed to bring those use cases into the real world. Cryptographers are, meanwhile, already preparing for the day when quantum computers might be used to crack the codes used, for example, to secure online access to bank accounts. So, even before quantum computing becomes widely used, 'post-quantum cryptography' is already here. 

IS GOOGLE IN THE LEAD?

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Google, with its 'quantum supremacy' headline, is staking a claim to leadership in the field but IBM is a close rival. Applied research is growing and startups are springing up too - it's possible to book time on a quantum computer hooked up to a cloud server to do research work. China, which has invested heavily in fields such as artificial intelligence, is also backing quantum computing - making it another front in its evolving trade and technology cold war with the United States.