A different, more powerful way of computing
Since the 1940s, the rules of computing haven't changed. Computers have continued to get smaller and faster year after year, but their fundamental operations remain the same. They still obey the laws of information processing, and process information by performing operations on bits. Quantum computers manipulate qubits instead of bits. With superposition and entanglement, the states of multiple qubits become very complex. By harnessing these complex states, quantum computers will be able to solve many problems much faster than today’s computers.
How to build a quantum computer
The idea of quantum computing works on paper, but we must be able to build one. This is much easier said than done. The difficulty comes from two opposite requirements:
The computer must be completely isolated from the world around it to protect the fragile state of the qubits;
We must be able to interact with the qubits to control them.
We need to find the right system that balances these requirements. Several prototypes of quantum computers already exist. Although they are not yet advanced enough to offer an advantage over digital computers, we are only at the dawn of the quantum age.
When to use a quantum computer
Unlike advances in digital computing, which add memory capacity or increase the speed of the processor, quantum computing dramatically alters how we solve problems at the fundamental level. Algorithms have to be re-designed from the ground up, and figuring out which problems benefit from using a quantum computer remains an active field of study.
There are many problems where quantum computers are expected to be no better than digital computers. For example, there is no evidence that a quantum computer will be better at running a word processor than a digital computer. Other problems are “easy” for digital computers already, such as multiplying two numbers together.
However, for certain problems, quantum computers can offer strong advantages. While multiplying two numbers together is easy for a digital computer, the reverse process (factoring) is much harder. Even the world’s most powerful supercomputers would take years to factor a 400-digit number. In 1994, Peter Shor proved that a large and robust quantum computer would be able to find those factors exponentially faster.
Quantum algorithms have also been discovered for tasks such as search and optimization, and are waiting for the right hardware to be run on. There are likely many more quantum algorithms that haven’t been discovered yet.