A RACE is underway to harness the spooky, counter-intuitive laws of ' quantum physics ' to build a new kind of computer.

For some tasks, a quantum computer could outperform any non-quantum machine that could ever be built, blazing through calculations in cryptography, chemistry and finance.

BUT when will a useful machine arrive?

One measure of a quantum computer's capability is its number of quantum bits, or qubits. But existing machines, which implement qubits in various different ways, all have a fatal flaw, the delicate quantum states on which they depend '' decohere '' after a fraction of a second.

A better measure may be so-called ''quantum volume'' [QV], which depends on the '' width '' of a computer [ its number of qubits ] and its '' depth '' [ the number of operations they can perform before decohering ]. 

A computer with 14 qubits that is able to execute 14 operations is said to have a QV of 2 to the power of 14, or 16,184.

The maximum QV achieved is rising steadily but the volume needed to perform useful operations, not just small-scale tests, remains unclear.

IBM, a leader in the field, has set itself a QV target of 2 to the power of 100. 

Like artificial intelligence, which disappointed for decades before its sudden, spectacular success,  quantum computing is likely to go from useless to ubiquitous very quickly - just as soon as researchers figure out how to turn up the volume.

The World Students Society thanks The Economist.


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