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Science

New State of Matter Boosts Quantum Computation 41

Posted by kdawson
from the string-net-liquid dept.
Matthew Sparkes writes "In theory, quantum computers can be superior to classical computers for some kinds of problems; in practice their building blocks, qubits, are extremely fragile. Even a slight knock can destroy information. A radical solution to this problem was proposed in the 80's — instead of storing qubits in properties of particles, such as an electron's spin, it was suggested that qubits could be encoded into properties shared by the whole material, and so would be harder to disrupt. Unfortunately, no material with the needed properties existed. Scientists now think they have made a material in the lab, thought to be an example of a new state of matter, that might do the trick. It's an ultra-purified form of a mineral, herbertsmithite, first discovered in Chile in 1972. Its electrons are arranged in a triangular lattice. Researchers say it could become the silicon of the quantum computing era."
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New State of Matter Boosts Quantum Computation

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  • Very cool material (Score:4, Insightful)

    by Gr8Apes (679165) on Thursday March 15, 2007 @09:25AM (#18360885)
    Unfortunately, while TFA is descriptive and informative, it reads more like a PR than a scientific paper. It sounds like everything still needs to be verified. The headline is certainly misleading, as no experiments of any sort have been done to prove that they can do any of the manipulations that are required to advance quantum computing.

    This is merely the very very early stages of basic research. Very interesting none the less.
  • Yes, it's new (Score:4, Insightful)

    by Ambitwistor (1041236) on Thursday March 15, 2007 @11:28AM (#18362537)
    In the traditional Landau paradigm, phases of matter arise as broken symmetries of the Hamiltonian, with different phases corresponding to different symmetries and described by a "local order parameter" (e.g. magnetization).

    With the advent of developments in high-temperature superconductivity and the quantum Hall effect, new phases were found that exist completely outside the Landau paradigm: topological order [wikipedia.org], in which there is no local symmetry, yet the topology of the system can globally distinguish one phase from another.

    Excitations of these systems with topological order were once thought to be necessarily "gapped", that is, the quasiparticle excitations have an effective mass. However, Wen has proposed a more general notion of "quantum order", in which gapless (massless) quasiparticles, analogous to photons or other gauge vector bosons, can appear.

    The mechanism by which this occurs, in Wen's paradigm, is through "string net condensation". In quantum field theory, from the work of Polyakov and others, it is possible to think of the field lines connecting particles as "strings", with the particles residing at the endpoints of the strings. The fields are gauge fields, so the "stringy" field lines correspond to the massless gauge bosons, as opposed to the massive matter particles that serve as the string endpoints. Wen's quantum order has excitations in a spin lattice correspond effectively to strings (massless "force field" quasiparticles), which are open, i.e., have endpoints (massive "matter" quasiparticles).

    There are actually strong analogies between these ideas and actual string theory (as noted by my reference to Polyakov's work). In fact, Wen did his Ph.D. in string theory under Edward Witten before switching to condensed matter.

    The work [arxiv.org] discussed in this story is an experimental demonstration of a system with gapless excitations that do not obey Landau's local order paradigm, and thus relate to Wen's work on quantum order. (I am fuzzy on the details so I don't know to what extent this work is a confirmation of Wen's theories. I also don't know how novel gapless excitations are without symmetry breaking.)

    You can read more about this from his work [arxiv.org], such as this [arxiv.org]. Wen has even proposed that perhaps the actual photons and electrons we think are real are really just quasiparticle excitations arising from a low energy (large scale) effective field theory of some underlying submicroscopic lattice that we can't see — see here [arxiv.org]: he can recover many (but not all) of the aspects of the particle physics this way, and argues that it unifies light and matter (since open strings always have endpoints). I think he has problems with chiral fermions, IIRC. The big stumbling block is of course gravity, although he has made efforts in that direction too (here [arxiv.org]). He has written a graduate textbook [mit.edu] on these ideas; he also has some talks up on his web page [mit.edu].

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