Dear Andre, Thorsten, Dusko, and others, Andre Joyal wrote:
Quantum information science is also quite speculative:
http://en.wikipedia.org/wiki/Quantum_Information_Science http://en.wikipedia.org/wiki/Topological_quantum_computer
It depends whether one is talking about: (1) having a quantum computer in the shops (2) theoretical discovery and experimental verification of new physical phenomena inspired by approaching nature in information-theoretic terms. While the first is indeed pure speculation, the second is a fact, with many recently discovered physical phenomena, some of which are embodied in terms of computational models, having effectively been established in the lab. Well-known examples are quantum teleportation and quantum key exchange. To mention one example of a phenomenon embodied in terms of computational model: the ability to universally alter the state of quantum systems by only relying on observations (= the measurement-based quantum computational model). Actually, certain guises of quantum information technology are effectively available for purchase at: ID quantique: http://www.idquantique.com/ MagiQ: http://www.magiqtech.com/MagiQ/Home.html Smart Quantum: http://www.smartquantum.com/SmartQuantum.html These three companies are not at all controversial, as opposed to for example D-Wave. There must be well over 1000 researchers active in the area which has its `own wikipedia': http://www.quantiki.org/wiki/index.php/Main_Page The general expectation would be that it are the quantum communication protocols which will be the first transitions to mainstream technology, and these may become components within some hybrid information processing device. Andre Joyal wrote:
But the mystery of quantum physics lies elsewere: the extraction of a probability distribution from the complex values of a wave function.
Thorsten Altenkirch wrote:
I agree that the big question in quantum theory is the "measurement problem".
The measurement-based quantum computational model is interesting in that it considers what for a long time was the most controversial ingredient of quantum theory, as the main processing resource: von Neumann's projection postulate which describes how the state changes under observation. These changes under observations of typically highly entangled states can be conveniently modeled by certain interacting Frobenius algebras in monoidal categories: http://arxiv.org/abs/0906.4725 http://arxiv.org/abs/0902.0500 I don't see any speculation here, just a convenient manner of representing physical phenomena which effectively have been observed in the lab, by using structures which are considered as category-theoretic. A software package to help with this is also under development: http://web.comlab.ox.ac.uk/people/Aleks.Kissinger/projects.html http://dream.inf.ed.ac.uk/projects/quantomatic/ In this context, recently Ross Duncan and Simon Perdrix solved an open problem in the area of measurement-based quantum computing, which has to do with guarantying a deterministic answer for certain sequences of measurements, and the formulation of the answer crucially relies on the Frobenius algebras. (their paper is forthcoming) Dusko Pavlovic wrote:
most physicists would probably say that they are happy with hilbert spaces. but many of them (albeit mostly theoreticians) ar enot.
In fact, it are the experimentalists which tend to get quite excited about the use of graphical languages to describe quantum phenomena since these are more `operational' than the usual Hilbert space treatments. Theoretcians have a harder time to denounce the things to which they are used, except when you are called John von Neumann and you crafted the Hilbert space quantum mechanical formalism a few years earlier. Best wishes for the new year, Bob. [For admin and other information see: http://www.mta.ca/~cat-dist/ ]