What’s inside a quantum processor?

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The D-Wave One quantum computer – technically known as a ‘quantum optimiser’ – works differently to classical computers in many ways. However, the most important is its abilities to use superposition – to put bits of information into more than one state at the same time – and its restating of mathematical problems in terms of a Hamiltonian – which is essentially the energy of the forces that move particles about.

It does this by manipulating the states of quantum bits (qubits) to set up the problem that needs solving through the use of couplers and programmable magnetic memory (PMM). Once the problem has been set up within the system, the D-Wave One then determines the answer by naturally evolving its system into its lowest-possible energy state.

This evolution into a lowest-energy state – or the ‘ground state’ – is key to the operation, as it highlights the avenue D-Wave has used in its system. Indeed, the reason why the computer is called a quantum optimiser is that it arrives at this energy ground state adiabatically (without the release or input of heat within the system). It does this by cooling its circuitry to 20 millikelvin (272.98 degrees Celsius/459.36 degrees Fahrenheit; near absolute zero) and building it out of a material known as superconductor. In doing this, the D-Wave One can create a direct passage from the initial programmed system state (ie the problem) to the system ground state (ie the answer) naturally and incredibly quickly, considering a range of different permutations simultaneously.

In essence, the D-Wave One reaches answers to questions by ‘tunnelling’ through an energy landscape directly to the landscape’s lowest-possible energy state. This can be likened to the passage of a golf ball on a golf course into a hole. The initial system’s state is the golf ball on a tee, the energy landscape the hills and valleys of the course, and the hole the ground state. To reach the hole (the answer) in a classical computer, the system – nonadiabatically – moves the ball over the obstacles into the hole. In the D-Wave One, meanwhile, the ball tunnels through the hills and over the troughs directly into the hole.

The D-Wave One is already demonstrating the immense possibilities of quantum computing, but it’s clear that there’s still a lot more potential to revolutionise computing.