

(Nearly) Visible Quantum Interactions - CoryOndrejka
http://arstechnica.com/science/news/2010/03/scientists-drag-quantum-mechanics-into-the-visible-realm.ars

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roundsquare
I read this and don't understand, but I want to. Can anyone explain?

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zbyszek
I'll make a start to the best of my understanding so that at least more
learned readers can correct me. In particular the Josephson phase qubit is
beyond my ken, really, so take this with a pinch of salt.

They have a lump of material which will vibrate when driven with microwaves.
The mechanical energy of this vibration is, like other forms of energy,
quantised. They cool it down so they can distinguish the ground and first
excited states.

The oscillator is piezoelectric, so they can get a current from it that
depends on the frequency of the oscillation, and this enables it to be coupled
to the qubit device.

The Josephson junction has two phases, superconducting and non-
superconducting. The junction in a circuit behaves like an oscillating
circuit. Transitions between these phases occur at certain resonant
frequencies which depend on the current applied. The resonant frequencies are
quantised and you can have a superposition of the states, and that's why this
is a qubit. The splitting between these quantum states depends on the current.

Coupling the piezoelectric oscillator with the qubit allowed them to drive a
circuit at frequencies that could change the qubit state. Conversely, the
state of the qubit can set the vibrational state of the oscillator. Since you
can set the qubit in a superposition of the ground and first excited state,
the ground and first excited states of the oscillator i.e. not vibrating and
vibrating, are also superposed.

