A beginner’s guide to quantum computing

Quantum computers are a pretty hot topic in science and technology news at the moment. Across major tech companies and smaller university departments around the world, people are trying to build a machine to revolutionise pretty much any problem that has lots of calculations involved. And those problem range from economic and climate models to molecular modelling and superstring theory and so, so much more.

The competition to build one has been dubbed “the space race of the 21st century” and some suggest that we’ll have one that works better than a normal computer within a decade.

Right now, the most major advances include IBM’s 50 qubit computer that can hold its state for 90 microseconds and their 20 qubit computer that’s open to public access for research and Google’s 72 qubit version, named Bristlecone … but hey, what do any of these terms mean?

 

Qubit and quantum weirdness

Short for ‘quantum bit’, differentiating it from a normal, “classical” computer bit. A classical bit holds information in binary by being switched to either 0 or 1. A qubit is more special because it can be both a 0 and 1 at the same time. A great analogy is that of a coin. It has heads on one side and tails on the other, but if you spin it on a table, it could be considered to be both heads and tails at the same time. The difference is that you could get a high-speed camera and check which side is facing you at a time, whereas a qubit is actually in both states at the same time.

This phenomenon is called superposition, but it doesn’t mean too much until we add in one other thing- entanglement. Entanglement is a way of instantaneously connecting particles and means that we can have two qubits, both in a superposition so they’re 0 and 1 at the same time and so between the two qubits they’re effectively in 00, 01, 10 and 11 states all at the same time. Add another entangled particle and there are 8 states, then 16, 32, 64, 128: doubling every time we add another qubit.

Simple calculations show that this continual doubling means that a computer with only entangled 100 qubits could outperform today’s supercomputers. So perhaps you’re thinking that we’re getting pretty close?

 

The problems

Not quite. The main challenge is keeping all those qubits in entangled superposition, which is actually very hard to do. Pretty much any movement will destroy this fragile state and particles almost always vibrate with kinetic energy. So that means cooling them down to a fraction of a degree above absolute zero (about -273.15 degrees Celsius) so that the particles won’t vibrate. And as you can imagine, it’s extremely difficult to get things that cold and to stay there.

IBM’s 50-qubit computer mentioned above could hold its entangled state for 90 microseconds before the entanglement falls apart (technical term is ‘decoheres’). The others don’t do much better and are rife with errors in their computations. This means extra qubits for “double-checking” calculations are required and we could need as many as 1000 qubits for the computer to practically useful.

 

To the future

But some people are great optimists for the future. Microsoft has designed a new programming language, Q#, for use to program a quantum computer so that people can start learning how we can effectively use this technology when it becomes an everyday reality.

And that reality is hopefully only a decade away before we can start to see this technology working to solve our real-world problems!

 


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