Saturday, 8 October 2011

Quantum Computing for the Determined

Moving Pictures

Nobody seems willing to predict when quantum computing will take off. Some are even beginning to question whether it will ever do so. Meanwhile, optimists patiently await that crucial breakthrough, the discovery of the perfect physical realisation of the qubit. There's no shortage of candidates. The Nitrogen Vacancy (NV) centre in diamond is one. NVs are the crystal lattice imperfections in pink diamonds that give them their hue. Then again, a lot of progress has recently been made involving trapped ion systems.

The optimists wait - impatiently, on second thoughts! - for one of these, or for some other exotic virtual particle inhabiting some material (or as yet unknown metamaterial), that will finally and abruptly realise the qubit as coherent, entangled and scalable.

As they wait, they polish their grasp of linear algebra, matrices, the various fundamental and second-order quantum "gates" that have been conceived, and the circuits made possible by these. Rehearse the limitations imposed by their fragility and inscrutability. Marvel at the astonishing algorithms that have been developed in qubit theory, while worrying about their scant number and opaque discoverability.

Almost to a man or woman, they have found and honed their new algebraic skills using The Book: Quantum Computation and Quantum Information, by Michael A. Nielsen (University of Queensland) and Isaac L. Chuang (IBM / Stanford University). Or Mike and Ike, as this revered tome is universally known. A literally pioneering work, it was the first of its kind, and is still today the standard to which all else is inevitably compared (my earlier review is here). In fact it's the most highly quoted physics publication of the last 25 years, and one of the ten most highly quoted physics books of all time (source: Google Scholar, December 2007).

In support of its tenth anniversary edition, Professor Nielsen has released a set of 22 short video lectures on his blog. They're a great introduction to the subject. However, he has stopped just short of completing the course, due to intervening work commitments. He has promised to complete it if there's enough interest in the videos produced so far. Here's the first one:

You know what you must do!

Next time: Single Qubit Gates.

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