Let’s start at the beginning. Computers, as you may know, are machines that automatically execute algorithms. They can be made from almost anything — you could, in theory, build a computer using water, or even dominos. Most modern computers, though, use silicon and electricity.
At the heart of all computers is the capability to use logic. That can be extremely simple. A rudimentary (perhaps domino powered) computer might have two inputs, A and B, and one output, X. If both inputs equal 1, then the computer outputs 1. If A and B have any other combination then it outputs 0.
This simple example is known as an AND gate. Mathematicians long ago worked out a whole series of similar logical actions. Modern, non quantum computers, are based around these logical gates, including AND, OR, NOR, XOR and many others.
From these simple foundations, computers can build up more complicated logical systems. A standard laptop CPU now contains billions of logic gates, all ticking away quietly in the background. The result is the ability to calculate all sorts of things, from city metro systems to the hearts of stars.
This, once computers became widespread, changed the world. Modern life is built on the ability of computers to perform endless calculations. But scientists also realised that, powerful as computers are, they are terrible at solving certain classes of problem.
In particular, computers are bad at simulating quantum phenomena. For science this was far from ideal. At the fundamental levels that current research focuses on, nature is quantum. It behaves in strange ways, and it turns out to be very hard to simulate.
Fully simulating a single atom for a single second, for example, requires enormous supercomputers and a huge amount of time. The idea that we can simulate more complicated quantum arrangements — say the molecules of a new drug — cannot be seriously considered at the present.
From this problem, the idea of a quantum computer was born. This would, simply, be a computer that could simulate quantum phenomena. With a truly quantum computer, simulating atoms would be easy and would take seconds instead of years. This, if it could ever be realised, would open up a new era of scientific research.
Since the idea first emerged, researchers have been hunting for a way to build a quantum computer. Many different approaches have been tried, and gradually the field has settled on a basic method of quantum computing. Though quantum physics is a broad field, one key aspect, superposition, is essential to understanding how quantum computers work.
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