However, Preskill's presentation was completely smooth, comprehensible, and filled with very entertaining animations in his PowerPoint presentation. And in many respects, it went well beyond my lecture.
He explained things like
- entanglement (this word comes from Schrödinger, by the way)
- decoherence
- history of these EPR things, including Schrödinger's reply to the EPR 1935 paper (described as the last Einstein's paper whose relevance survived to the present days): did you know that the "spooky action at a distance" is even spookier in German? It is "spukhafte Fernwirkungen" :-)
- difference between bits and qubits, and the difference between (red) boxes and (red) soxes :-)
- explanations why the quantum computers can be faster, with the factoring algorithms as examples
- quantum cryptography and a safe transmission of the key to encode information - in a detailed way that makes all the necessary steps transparent; Alice and Bob were exchanging secret data while Eve (...) was eavesdropping ;-)
- history of quantum computation
- the nature of basic operations of quantum computers
- methods of error corrections - with a beaver trying to undo the errors introduced by a dragon
- basics of technical realizations of the quantum computers with ion traps (if I remember well) as the main example
He has also become famous for having won the bet against Stephen Hawking; a well-deserved victory. Hawking used to argue that the information must be lost after a black hole evaporates. This followed from Hawking's semiclassical calculations but the rules of quantum mechanics - namely unitarity - dictated otherwise and John Preskill correctly decided that the postulates of quantum mechanics are primary.
Preskill is also a poet. Howard Georgi who introduced the speaker mentioned that Preskill's poem could also be thrown into a black hole. Fortunately, the information is preserved anyway, as argued below, which is why Georgi's efforts won't lead anywhere. You can compare Preskill's poem with a poem by a Nobel prize winner who will speak in the same room at the same time next week.
Mostly because of the convincing developments in string theory where black holes are found as objects within a completely unitary, quantum mechanical framework (and the case of the AdS/CFT correspondence may be even more convincing than Matrix theory and other approaches), Hawking decided that the main argument for the information loss, namely that it should be impossible to construct a consistent unitary theory which agrees with black hole physics in the semiclassical approximation, has been shown incorrect, and his bet is effectively lost. Hawking has bought Preskill an encyclopedia of Preskill's choice, namely an encyclopedia of baseball.
Note that this bet could only be ended because Hawking turned out to be very reasonable. If Preskill had made a bet against Peter Woit or someone like that, he would be told that no arguments for unitarity exist and the arguments based on string theory do not exist either because the existence and insights of string theory can simply be denied and pictured as an uncertain source of knowledge about quantum gravity. And Peter Woit would undoubtedly use even stronger and sillier words. ;-) In reality, string theory has shown its ability to authoritatively answer deep questions about quantum gravity such as the information loss paradox, and only complete outsiders misunderstand that these general insights are established despite our ignorance about the detailed choice of the vacuum. Yes, they are established by pure thought, if you need to hear it.
Finally, I want to say that without any exaggeration, John Preskill belongs to the top five best physics communicators in this world. Be sure that I haven't written this sentence more than five times in the last 10 years. He is a fast thinker who knows how to analyze things in details, present them in a completely comprehensible fashion, and answer the questions that appear along the way.
