Full house

Last week back to a full house at the Royal Institution to hear all about quantum computing. A team of four made up of a science journalist, loud in the way of presenters on educational television programmes, the deputy ambassador of the Kingdom of the Netherlands, Professor Ekert, a Pole from the city that used to be called Breslau, and Professor Burhman, a Dutchman who is, inter alia, a big cheese in Qusoft (see reference 1).

Started off in the rain with a fine rainbow to be seen in the east from Meadway. Plus a chunk of a second rainbow to the right of the first.

Got to a very busy Vauxhall, perhaps because at 1730 or so we were a touch earlier than usual and rush hour was at full rush.

Out at Green Park to admire the shops in Albemarle Street. One of which at the Green Park end had such flashy shop girls that one shuddered to think what one might be paying for the merchandise. We passed up on an opportunity to spend £2,500 on a rather splendid boat made out of matchsticks, a sort of cross between a Chinese junk and a Portuguese carrack.

Refreshment at the Goat, where, for the first time I took note of the decorative scheme. First floor bar, astronomical pictures celebrating the proximity of the Royal Institution. Stairs, arty pictures celebrating the proximity of the Royal Academy. Ground floor bar, I forget. Must look next time.

The deputy ambassador turned out to be a lady lawyer who managed a short and witty talk in heavily accented English, reminding us on the way that the Dutch Republic won more of its wars with us than it lost, some consolation I suppose for the fact that the Dutch Republic rather sank from view thereafter. She was there because her embassy was sponsoring a series of talks at the Institution, of which this was the first - with a further attraction being drinks after, of which we did not, as it happens, partake, the Rifleman of Epsom having had first refusal.

Both professors were very good, with around 25 minutes each, both managing the difficult trick of being both eminent and accessible. I am a little confused now about who said what, but I think the basic divide was Ekert first on theory, Burhman second on practise.

Ekert started with what I now know to be the famous double slit experiment and the destruction of the basic law of probability which says that the probability of the union of two quite different events is the sum of the individual probabilities of the two constituting events, by adding an error term involving the cosine of the phase difference of those two events, which means that the error term might be positive or negative.

While today, Bing fails to turn up anything of the sort, merely suggesting that the double slit experiment proved the dual nature of matter, both particle and wave. Reference 3 was short but still much too much for my rusty algebra, while reference 4 was promising but failed to contain sines or cosines.

Nevertheless, his story was that quantum computing was all about exploiting the vagaries of this error term.

Burhman told us that Google might have built a computer which ran 72 qubits, and consisted mainly of high grade refrigerator, while 100 qubits would be bigger than any other computer presently on the planet. The problem was learning how to program the things. This depending on an instruction set with included instructions with intriguing names like the square root of NOT and the square root of SWITCH. Bing does know about them, but I do not, myself, yet know any more than the names. Maybe that will come.

One of the two of them even managed a joke about a puzzle about three light bulbs in one room, their three switches in another and one visit to each room. It seems that an eminent mathematician completely failed to solve the puzzle, going to far as to prove it could not be solved using the incompleteness theorem (or something of that sort), to have the maintenance man do it in a few seconds.

So a week out, I do not seem to have learned very much. But my curiosity has been aroused and I may be moved at some point to look up and read about some of the stuff that they had been talking about. So far I have learned that the state of a qubit is described by a pair of complex numbers, so a much more complicated object than the state of an ordinary bit which can only be zero or one.

Out to find that the fancy book shop which used to be at the corner of Stafford Street and Dover Street has gone. Gone for long enough for it to be a building site on Street View.

Singularly disgusting old man snuffling his grub out of a paper bag on the train. Far worse than the average young man at the same game.

Wound up the evening with a discussion about the peculiarities of yew trees, box trees and hazel nut trees at the aforementioned Rifleman.

Reference 1: http://www.qusoft.org/.

Reference 2: https://en.wikipedia.org/wiki/Qubit.

Reference 3: https://en.wikipedia.org/wiki/Quantum_probability.

Reference 4: https://plato.stanford.edu/entries/qt-quantlog/.