How Does a Quantum Computer Work?

Quantum computers are almost here and will have far ranging benefits and impacts, so what’s all the fuss about and how does a quantum computer work?

Classical computers generally have to consider each possible outcome individually when working through complex simulations. It’s a drawback that makes them slow and inefficient when resolving problems especially when a very large number of possible outcomes or interactions need to be worked through and considered.

When quantum computers are used to tackle similar problems, they do so by firstly using qubits to go into a superposition of all the possible states. Quantum circuits can then be used to encode all the rules that apply to the problem using quantum logic gates. The program is then simulated many times which results in a small set of likely solutions. So, how does it come up with the small set of likely solutions?

When you encode a problem into a quantum computer you’re applying and manipulating the spin direction and phase of your qubit states. The quantum phase is the quantum state of the particle and this can be changed with quantum gates. When waves are in phase the amplitudes add and when they’re out of phase they cancel. Interference is used to amplify some answers and cancel other answers and eventually you arrive at a small number of likely solutions. The likely solutions can then be individually back tested to see if they solve the problem being attempted.

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