What are quantum computers and how do they work?
An article by Cambridge Coding Academy alumna, Apoorva Verma.
Google, IBM, Microsoft and several start-ups are competing to create the next generation of supercomputers. Quantum computers will be much more powerful than the classical computer and help us solve problems, like modelling complex chemical processes. However, the quantum future is not going to come easily and when it does there is no knowing what it’ll look like. Currently companies and researchers are using a handful of different approaches to try and build the most powerful computers that the world has ever seen.
The limits of classical computers
The transistor is a binary switch and is the fundamental building block of classical computers. Now that we have made transistors almost as small as an atom, we need to find an entirely new way to think about and build computers. Although the classical computer helps us do many things, inside it’s just really a calculator that uses a sequence of bits — 1’s and 0’s to represent two states — to make sense of, and decisions about, the data we input following a set of prearranged instructions. Quantum computers are not intended to replace classical computers, they are expected to be another tool that we can use to solve complex problems that are beyond the capabilities of a classical computer. We are entering a world in which the amount of information we need to store is growing and more transistors are needed to process it. Classical computers are largely limited to carrying out one task at a time, so a more complex problem will take longer. A problem that requires more time and power than can be provided by today’s computer is called an intractable problem. These are the problems that quantum computers are predicted to solve.
How does a quantum computer work?
Quantum computers take advantage of the strange ability of subatomic particles to exist in more than one state at one time. Due to the way these particles behave, tasks can be completed much faster and with less energy than a classical computer.
In a classical computer, a bit is a single piece of information that can exist in two states: 1 or 0. Quantum computers use quantum bits or ‘qubits’ instead. These are quantum systems with two states, however — unlike the usual bit — they can store much more information than just 1 or 0 because they can exist in any superposition of these two values.
A qubit can be thought of like an imaginary sphere. Whereas a classical bit can be in two states — at either of the two poles of the sphere — a qubit can be any point on the sphere. This means a computer using these bits can store a huge amount of information using less energy than a classical computer.
What can a quantum computer do?
Quantum computers operate on completely different principles to existing computers, which makes them really well suited to solving particular mathematical problems, like finding very large prime numbers. Since prime numbers are so important in cryptography, it’s likely that quantum computers would quickly be able to crack many of the systems that keep our online information secure. Due to these risks, researchers are already trying to develop technology that is resistant to quantum hacking. On the other hand, it’s possible that quantum-based cryptographic systems would be much more secure.
Researchers are also excited about the prospect of using quantum computers to model complicated chemical reactions — a task that conventional supercomputers aren’t very good at. In July 2016, Google engineers used a quantum device to simulate a hydrogen molecule for the first time, and since them IBM has managed to model the behaviour of even more complex molecules. Eventually, researchers hope they’ll be able to use quantum simulations to design entirely new molecules for use in medicine.
List of sources/references:
- http://www.wired.co.uk/article/quantum-computing-explained
- https://spectrum.ieee.org/tech-talk/computing/hardware/20-entangled-qubits-brings-the-quantum-computer-closer
- https://www.forbes.com/sites/bernardmarr/2017/07/04/what-is-quantum-computing-a-super-easy-explanation-for-anyone/#14154a2d1d3b
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