By Artur EKERT

Chania, a picturesque little town on the coast of the western Crete, the birthplace of Dimitris Angelakis, the main organizer of this Advanced Study Institute in Quantum Information Science, is only a few miles away from the tiny island of Antikythera. In 1900 a party of sponge-divers were driven by a storm to anchor near the island and there, at a depth of some 40 meters, they found the wreck of an ancient cargo ship. Among the pieces of pottery and marble statutes sprawled on the seabed was a coral-encrusted lump of corroded bronze gear wheels. The Antikythera mechanism, as it is now known, was probably the world's first “analog computer” — a sophisticated device for calculating the motions of stars and planets. This remarkable assembly of more than 30 gears with a differential mechanism, made on Rhodes or Cos in the first century B.C., revised the view of what the ancient Greeks were capable of creating at that time. A comparable level of engineering didn't become widespread until the industrial revolution nearly two millennia later. Thus it is hardly surprising that Richard Feynman, who saw the Antikythera mechanism on display in Athens, called it “nearly impossible”. In one of his letters, reprinted in “What Do You Care What Other People Think?: Further Adventures of a Curious Character”, he wrote

“… Yesterday morning I went to the archaeological museum. … Also, it was slightly boring because we have seen so much of that stuff before. Except for one thing: among all those art objects there was one thing so entirely different and strange that it is nearly impossible. It was recovered from the sea in 1900 and is some kind of machine with gear trains, very much like the inside of a modern wind-up alarm clock. The teeth are very regular and many wheels are fitted closely together…”

It seems likely that the Antikythera tradition of complex mechanical technology was transmitted via the Arab world to medieval Europe where it formed the basis of clockmaking techniques. As such, the Antikythera mechanism is a venerable precursor of mechanical computing devices based on the meshing of metal gears. Indeed, for many years the basic raw material of the computer industry was brass. The 17th century calculators of Wilhelm Schickard, Blaise Pascal and Gottfried Wilhelm Leibniz testify to the importance of gears in the history of computing. When, in 1837, Charles Babbage was tinkering with a design of the first programmable computer, known as the Analytical Engine, he was thinking in terms of rods, gears and wheels.

From gears to relays to valves to transistors to integrated circuits and so on – in the 20th century brass gave way to silicon. Today's advanced lithographic techniques can etch logic gates and wires less than a micron across onto the surfaces of silicon chips. Soon they will yield even smaller components, until we reach the point where logic gates are so small that they consist of only a few atoms each. If computers are to continue to become faster (and therefore smaller), new, quantum technology must replace or supplement what we have now, but it turns out that such technology can offer much more than smaller and faster microprocessors. It can support entirely new modes of computation, with new quantum algorithms that do not have classical analogues.

The very same person who was so fascinated by the ancient Antikythera laid down the foundations of quantum computation. In 1981 Feynman observed that simulations of some quantum experiments on any classical computer appear to involve an exponential slowdown in time as compared to the natural run of the experiment. Instead of viewing this fact as an obstacle, Feynman regarded it as an opportunity. If it requires so much computation to work out what will happen in a complicated quantum experiment then, he argued, the very act of setting up an experiment and measuring the outcome is tantamount to performing a complex computation. After all, any real computation is a physical process, be it classical or quantum. Thus any computation can be viewed in terms of physical experiments which produce outputs that depend on initial preparations called inputs. Since then, the hunt has been on for interesting things for quantum computers to do, and at the same time, for the scientific and technological advances that could allow us to build quantum computers.

The NATO Advanced Study Institute in Chania brought together a number of researchers and students in both experimental and theoretical quantum information science. During lectures and talks, and in numerous discussions over Raki, the participants shared their views on just about everything; from quantum algorithms and intricacies of computational complexity to the finer parts of Cretan cuisine, and from new technologies for realizing quantum computers to the spirit of traditional Greek dances. The knowledge that nature can be coherently controlled and manipulated at the quantum level was perceived as both a powerful stimulus and one of the greatest challenges facing experimental physics. Fortunately the exploration of quantum technology has many staging posts along the way, each of which will yield scientifically and technologically useful results and some of them are described in this volume.

We hope this collection of papers provides a good overview of the current state-of-the-art of quantum information science. We do not know how a quantum Antikythera will look like but all we know is that the best way to predict the future is to create it. From the perspective of the future, it may well be that the real computer age has not yet even begun.

We also wish to thank our sponsors NATO, the Cambridge-MIT Institute, the Union of Agricultural Cooperatives of Kidonia and Kissamos, the Cooperative Bank of Chania, ANEK Lines, Olympic Airways, ABEA Olive Oil Products and Stigmes Magazine. Finally we acknowledge the helpful collaboration from IOS Press in the publication of this volume and also thank Kaija Hampson for being an excellent secretary during the meeting.