- Quantum computers would exploit the strange rules of quantum mechanics to process information in ways that are impossible on a standard computer.
- They would solve certain specific problems, such as factoring integers, dramatically faster than we know how to solve them with today’s computers, but analysis suggests that for most problems quantum computers would surpass conventional ones only slightly.
- Exotic alterations to the known laws of physics would allow construction of computers that could solve large classes of hard problems efficiently. But those alterations seem implausible. In the real world, perhaps the impossibility of efficiently solving these problems should be taken as a basic physical principle.
Haggar Physicists Develop ‘Quantum Slacks,’ ” read a headline in the satirical weekly the Onion. By exploiting a bizarre “Schrödinger’s Pants” duality, the article explained, these non-Newtonian pants could paradoxically behave like formal wear and casual wear at the same time. Onion writers were apparently spoofing the breathless articles about quantum computing that have filled the popular science press for a decade.
A common mistake—see for instance the February 15, 2007, issue of the Economist—is to claim that, in principle, quantum computers could rapidly solve a particularly difficult set of mathematical challenges called NP-complete problems, which even the best existing computers cannot solve quickly (so far as anyone knows). Quantum computers would supposedly achieve this feat not by being formal and casual at the same time but by having hardware capable of processing every possible answer simultaneously.
This article was originally published with the title The Limits of Quantum Computers.