How a quantum computer is different from your laptop, explained by a scientist © Getty Images

How a quantum computer is different from your laptop, explained by a scientist

A beginner’s guide to the bizarre physics that powers quantum processors.

Your laptop, like all conventional computers, manipulates electricity within its silicon chips. Tiny amounts of electrical current are turned on or off, representing logical signals true and false, or binary numbers one and zero. All conventional computer hardware is based on logical operations on binary digits (bits) for that reason.

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However, quantum computers manipulate individual quantum elements such as electrons or photons, which in this context are called qubits.

It’s the weird quantum properties of these tiny particles that give quantum computers their power. For instance, due to their ‘spin’, electrons may be up or down – and photons may be vertical or horizontal – at once.

This ‘quantum superposition’ means that a qubit is in both states simultaneously. Well, that is until it interacts with some external factor that will then cause its state to become set – any vibration or disturbance nearby can cause these collapses.

To prevent such quantum decoherence, scientists try to preserve the fragile superposition states of qubits in vacuum chambers and fridges colder than outer space. Qubits also rely on a weird property known as entanglement, where the property of one particle is entangled with another.

This is where it gets really complicated. If we make two entangled particles with total spin of zero and the state of one particle collapses such that its spin is clockwise, the state of the other particle will be anticlockwise – even if the two particles are nowhere near each other.

All this basically means is that, once entangled, qubits can be used to represent huge numbers of possible numbers at the same time. For instance, Google’s quantum computer Sycamore had 53 qubits, which can represent more than 10,000,000,000,000,000 (10 quadrillion) combinations simultaneously. This meant it could perform a calculation in 200 seconds that would take an ordinary computer 10,000 years.

In theory, this means that a quantum computer could perform specialised calculations that are out of reach of conventional computers (a concept called quantum advantage or supremacy). But due to the delicate storage conditions required, there’s still a long way to go before we can have quantum processors in our laptops.

Asked by: Kamila Makin, Manchester

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