Question: What are some good uses for quantum computers

Chris Mansell answered on 16 Jun 2013:

Quick answers:

1. Quickly searching large databases.
2. Breaking codes such as the ones that prevent criminals hacking into your bank account whenever you buy something online.
3. Quickly equations.
4. Understanding material science and chemistry.
5. Doing the calculations needed in particle physics research (particle physics is what is investigated at the Large Hadron Collider)

Further explanations. Some require some maths concepts, such as proportionality, factorisation, etc.

1. The larger a database is the longer it takes to search it. We can call the number of items in a database, N. For an ordinary computer, the time to find what you’re looking for is proportional to N. For a quantum computer, the time is proportional to the square-root of N. So, for large N, quantum computers are much faster.

2. Today’s best codes are based on the assumption that there is no way to quickly find the prime factors of a (large) number. Whenever computers get faster, people just use a larger number in their codes. However, quantum computers are so fast that this wouldn’t be a problem for them. For the task of factorisation, quantum computers are “exponentially faster” than ordinary computers. (This has a precise meaning that I can explain if you want but I just wanted to use the phrase because I think it sounds impressive.)

3. This is another task for which quantum computers are “exponentially faster” than ordinary computers. If any of you have seen questions like the following in your maths books, you’ll know the type of questions I am talking about: Tim and Chris have five apples; Tim has one more apple than Chris; how many apples does Tim have? (Also written as: x + y = 5; x – y = 1; find x.) These equations are called “simultaneous equations.”

4. Physicists understand how atoms behave when they are on their own (the atoms, not the physicists). They know how atoms interact with each other. However, when there are lots of atoms in a chunk of material or a big molecule then you need to calculate how every atom will interact with almost every other atom. This is a lot of interactions. Ordinary computers can’t handle this amount of calculation but a quantum computer would be a lot better suited to doing this.

5. This is another task for which quantum computers would be “exponentially faster.”