Clegg Brian - Quantum Computing

In 1840, the British inventor and polymath Charles Babbage gave a number of lectures in Turin, taking as his subject an as-yet-unconstructed device, the Analytical Engine. Born in 1791, Babbage had a sufficiently large inheritance from his father a goldsmith and banker never to need to take gainful employment. He enjoyed the social life of the salon as much as his work. It is said that his inspiration to explore mechanical means of calculation was helping out his friend, the astronomer John Herschel, to check astronomical tables. The experience was tedious beyond measure and Babbage is said to have cried out, I wish to God these calculations had been executed by steam!

Had the Analytical Engine ever been built, it would arguably have been the worlds first computer in the modern sense of the word. Babbage had been playing the role of a computer for Herschel that is, a person who undertook calculations. The terminology dates back at least to the seventeenth century it was only in the mid-twentieth century that the term was shifted from human beings to machines. Although it was entirely mechanical, the Analytical Engine was intended to hold both its data and its programs on punched cards, based on the cards that had been devised to produce intricate patterns on the Jacquard silk-weaving loom. Unlike its semi-constructed (but never finished by Babbage) predecessor, the Difference Engine, where the instructions on what to do with the data were built into the machinery, the Analytical Engines instructions could be varied to taste.

Two years later, in an impressive piece of internationalism, a minor Italian military engineer Luigi Federico Menabrea (later to unexpectedly become Prime Minister of Italy) published a write-up of Babbages Turin talks, written in French for a Swiss publication, the Bibliothque Universelle de Genve. Left in that periodical, this memoir would no doubt have rapidly disappeared into obscurity. However, in 1843 it was translated into English by Ada King, the Countess of Lovelace. In truth, translation is a distinctly weak term for the resultant document, as King added copious notes that tripled the length of the piece, speculating on the future use of the unbuilt Analytical Engine and describing how it could be programmed for a number of tasks.

It is thanks to this single document that Ada Lovelace, as King is usually known, has gained the reputation of being the worlds first computer programmer. There is no doubt that Lovelace succeeded in bringing the potential of the Engine to a wider audience, though the degree to which she was indeed the first programmer has been disputed. One certainty is that the machine these instructions were intended for was never built realistically, it could not have been constructed with the mechanical tolerances of the time. And so, strictly speaking, we should say that the document contained algorithms, in the form of tables that reflected the structure of the Engine, rather than computer programs in the modern sense.

Algorithms are structured instructions that could be anything from the sequence of actions required to brew a cup of tea to complex manipulations of data to solve a mathematical problem. They dont require any computer they can be worked by hand but can, as was the case here, be structured in such a way that they fit well with a computers architecture.

Unfortunately, in the entirely desirable urge to provide good female role models from the past, Lovelaces contribution has been exaggerated. Lovelace was the daughter of the poet Lord Byron and Annabella Milbanke. As a child, Lovelace was encouraged by her mother to study mathematics. She is often described as a mathematician, but it would be accurate to describe her as an undergraduate-level maths student. From letters between Babbage and Lovelace, it seems well-established that the notes that Lovelace added to Menabreas work were strongly influenced by Babbage. And even taking algorithms as programs, we know that Lovelace was not the first. This is because, as historian of science Thony Christie points out:

The Menabrea Memoir that Ada had translated already contained examples of programs for the Analytical Engine that Babbage had used to illustrate his Turin lectures and had actually developed several years before. The notes contain further examples from the same source that Babbage supplied to the authoress. The only new program example developed for the notes was the one to determine the so-called Bernoulli numbers.

We do know that Babbage, in his lectures, described algorithms that could have become programs for the Analytical Engine, had it ever been built. Usually with a totally new piece of technology like this we have to wait for some kind of prototype to be constructed before we can be certain of the devices capabilities. But, remarkably, the Analytical Engine algorithms clearly showed the remarkable power that the machine would be capable of, had it ever been built. Rather than wait for programs to be developed, the Engine could instantly leap into action.

Having algorithms that were ready to go on a technology that was impossible to construct at the time was remarkable. That such a thing should happen twice seems even more surprising. Yet 153 years after the publication of Lovelaces translation and notes, a very similar occurrence would play out. This time, the imagined engines in question would invoke the power of the quantum.

By 1996, electronic computers had been part of government and business establishments for decades, and had become relatively commonplace in homes, since personal computers moved from the realm of enthusiasts toys to commercial products in the 1980s. Unlike the Analytical Engine, electronic computers were too complex to be designed by a single person and although some early programs were the work of an individual, many were constructed by teams.