Sunday, 1 June 2008

Given time...

One of the nicest (in the proper sense) comments made by Brian Cox in his talk on Cern was concerning our being.

'..This is what Hydrogen and Helium can do given 13.7 billion years...'

Hydrogen doing what it does best under terrestrial conditions.

The mind numbing combinations of events that must 'fall right' in order that we are able to write and read this blog, feel so unlikely as to fit neatly into Clarke's rules:

  1. When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.
  2. The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
  3. Any sufficiently advanced technology is indistinguishable from magic.
There are many occurrences of our being asked to perform 'Seemingly impossible tasks' or 'Endure impossible hardship'. Our accidental occurrence would seem to put these glib statements into perspective.

Helium doing what it does best under terrestrial conditions

Quite apart from the questionable enjoyment to be gained from this activity, Helium is contributing to the 'full circle' nature of it's use in Quantum Computing.

The question at the heart of every atom is being explored as a potential gate for decision making at an inconceivably small scale.

Go on, humour me, read it, it's not necessary to understand it. Just imagine it being spoken by Professor Frink from The Simpsons!

Qubits and quantum gates with electrons on helium
M.I. Dykman, B. Golding, P.M. Platzman (Department of Physics amp; Astronomy, Michigan State University), D.A. Lidar, L.-A. Wu (Chemistry Department, University of Toronto)

It was previously proposed that electrons floating on the surface of liquid helium can be used to make a quantum computer (QC). This computer will be scalable, with an interelectron (interqubit) distance \sim 1\mum, and the working frequency \sim 1~GHz. However, interaction between the qubits cannot be turned on and off. Instead the transition frequency of a qubit can be varied in a controlled way, so that the qubits can be tuned in resonance with microwave radiation for specified times. We show that the effective Hamiltonian of the qubits corresponds to an anisotropic Heisenberg spin system with a superimposed on-site static field and a pulsed perpendicular ac field. We describe an efficient way of interqubit excitation swap by selectively tuning qubits in resonance with each other. Relaxation of electrons is analyzed in the case where lateral electron confinement is due to underlying electrodes rather than the external magnetic field. Methods to further reduce the already small decoherence rate are discussed. These methods include an encoding into a decoherence-free subspace, in conjunction with decoupling ("bang-bang") and recoupling operations on the encoded qubits. Encoded recoupling also allows us to eliminate undesired single-qubit phases and qubit-qubit interactions that arise from the Coulomb coupling.

Well, it made me laugh!


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