Read more: “Instant Expert 33: Quantum information“
No overview of quantum computing would be complete without an attempt to answer the $64,000 (or possibly much more) question: are we likely to see working quantum computers in our homes, offices and hands any time soon?
That depends largely on finding a medium that can encode and process a number of qubits beyond the 10 or 20 that current technologies can handle. But getting up to the few hundred qubits needed to outperform classical computers is largely a technological issue. Within a couple of decades, given improvements in cooling and trapping, as well as coupling with light, existing technologies of trapped ions and cold atoms may well be made stable enough in large enough quantities to achieve meaningful quantum computation.
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The first large-scale quantum computers are likely to be just that: large-scale. They will probably require lasers for qubit manipulation and need supercooling, so are unlikely to appear in our homes. But if the future of much computing is in centralised clouds, perhaps this need not be a problem.
When it comes to anything smaller, the elephant in the room is entanglement, which is a fragile good at the best of times and becomes harder and harder to maintain as the quantum system grows. It would aid the progress of quantum computing if our assumption that entangled states are an essential, central feature turned out to be wrong. This intriguing possibility was raised in 1998 with the development of “single-qubit” algorithms. These can solve a large class of problems, including Shor’s factorisation algorithm, without the need for many entangled qubits. That would be a remarkable trick if it could be pulled off in practice – although Grover’s all-important database-search algorithm might still not be implementable in this way.
Some people believe that the fragility of quantum systems will never allow us to implement quantum computation in the sort of large, noisy, warm and wet environments in which we humans work. But we can draw hope from recent evidence that living systems – such as photosynthesis in bacteria and retinal systems for magnetic navigation in birds – might be employing some simple quantum information processing to improve their own efficiency.
If we can learn such secrets, a quantum computer on every desktop and in the palm of every hand no longer seems so fanciful an idea.
This article appeared in print under the headline “Are we nearly there yet?”
