Anushka Dhingra examines Google’s claim of quantum supremacy by diving into what the quantum computer achieved, how it did so, and how quantum computing actually works.
In late 2019, Google took a ‘quantum leap’ in the field of computer science, and claimed ‘quantum superiority’ by leveraging its quantum computer, Sycamore, to solve a problem which is virtually impossible for regular machines. According to John Martinis, an experimental physicist at the University of California, the complex computation which took Sycamore around 200 seconds to complete, would have taken traditional machines around 10,000 years. The calculation that Google’s computer has successfully completed is a quantum equivalent to creating an extensive list of random numbers, and rechecking their values more than a million times. While this does not have considerable significance outside the world of quantum computation, it is a big advancement in enhancing a device’s processing power.
How is this quantum computer different?
The word quantum ‘computer’ is a bit misleading, because when people think of computers, they think of a phone or a laptop. However, phones, laptops, and even powerful supercomputers all function on the same fundamental rules, whereas a quantum computer is significantly different.
What does it mean to achieve quantum supremacy?
To demonstrate quantum supremacy, Google followed three steps. First, they picked a circuit, second, they ran it on the quantum computer, and third, they simulated what the quantum computer is doing on a classical computer. Gradually, they increased the complexity of the circuit, till the point it became virtually impossible for the classical computer to keep up. At that point, Google claimed quantum supremacy.
How does this computer work?
The classical ‘bit’ stores information as a 0 or 1, while a quantum bit, or qubit, can exist as both 0 and 1 at the same time. A pair of classical bits can store one of four possible combinations of states (11, 00, 10, 01), but a pair of qubits can store all four combinations. This grows exponentially, with three qubits storing eight combinations, and four qubits storing 16. And when these qubits are inextricably linked, in theory, this interference between their wave-like interference can be leveraged to perform calculations that could otherwise take millions of years.
Physicists predict that one day quantum computers will be able to run revolutionary and complex algorithms, like finding data from large databases or factoring large numbers, like those used during the encryption process. However, this is still decades away, as running these algorithms and functioning general purpose machines requires millions of qubits, and the more qubits that are linked, the harder it is to maintain their fragile state during the device’s operation. Currently, Google’s algorithm runs on the Sycamore chip made of only 53 qubits, each composed of superconducting loops.
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