Quantum computers don't exist . . . yet. But if and when scientists develop the ideas behind quantum computing to create a practical product, the implications will be staggering. Quantum computers could, in a matter of minutes, perform certain types of calculations that would take millions of years on classical computers. Some scientists even speculate that quantum computing may finally make genuine artificial intelligence possible. Scientists have a lot of bugs to work out first, though.
The Weird Nature of Quantum Mechanics
To understand why quantum computers could offer so much computational advantage over classical computers, you have to understand a bit about the strange nature of matter on a sub-atomic level. You may be familiar with the example of Shroedinger's cat: if a cat is in a box and its life or death depends on the state of a subatomic particle following quantum mechanics rather than classical mechanics, then the cat is simultaneously both alive and dead, until we open the box and observe the results. This is difficult to conceptualize, and the example of the cat is not intended to be taken literally. The point is that while on a macroscopic level matter must be in either one state or another, subatomic matter can exist in different states simultaneously.
Bits and Qubits
In classical computing, the bit is the basic unit of information. A bit is binary. It's in one of two states: zero or one; off or on; plus (+) or minus (-). With quantum computing, the basic unit of information is the qubit, which can exist simultaneously as both zero and one. This is difficult to understand because it conflicts with our standard macroscopic view of reality. But think about three bits of information. Each of the three bits has two different states, so three bits can describe one of eight different states (2^3). Three qubits exist in all eight different states simultaneously. One way to conceptualize this is to think of the qubits existing in eight different universes. So when you perform operations on these three qubits, you are performing operations on all eight states simultaneously. An operation on four qubits would act on 16 values simultaneously. Each additional qubit doubles the number of simultaneous operations performed.
Quantum Parallelism
Computer scientists already make use of parallelism by breaking a problem down and having separate computers work on a piece of the problem. A thousand different computers could perform a complex calculation in a thousandth of the amount of time a single computer would take to perform the same calculation on its own. But for really difficult problems, like factoring a number with several hundred digits, there aren't enough computers on the entire planet to perform the calculation in a reasonable amount of time. But a quantum computer could essentially run the problem in billions of different universes simultaneously, a phenomenon known as quantum parallelism.
Implications
Most modern cryptography is based on factoring large numbers, which is far too complicated for computers today to accomplish in a reasonable amount of time. As a result, cryptographers have little concern that computers can crack their codes. Quantum computers could change that. For example, factoring a 1,000 digit number would take 10 million billion billion years on the best computers we have today. Even running a billion of these computers in parallel could, at best, reduce the time by a factor of a billion, so you'd still be waiting 10 million billion years. But, theoretically, a quantum computer could do it in 20 minutes. If quantum computers become a reality, computer security as we know it could essentially evaporate. But serious and complicated technical problems remain to be solved. So we don't have to worry about quantum computer hackers. Yet.
Tags: computers could, different states, amount time, eight different, quantum computer, Quantum computers