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In my laboratory, I have already obtained a polarization-entangled photon source. It was created via the Spontaneous Parametric Downconversion process of 2 BBO crystals. The next question is that would I be able to use this source to create qubits? If so, how?
Thank you in advance.
Any photon (pure) state may be described by a q-bit formalism: $$|photon\rangle = \alpha |0\rangle + \beta|1\rangle$$ where $|0\rangle$ and $|1\rangle$ represent the two possible polarizations of the photon.
So, any photon "is" a q-bit. You don't have to "create" q-bits. Just prepare photons is some state.
An entangled state of $2$ photons may be described by a $2$-photons ($2$-qbit) state, for instance :
$$|entangled\rangle = \frac{1}{\sqrt{2}}(|0\rangle|0\rangle + |1\rangle|1\rangle)$$
As Trimok says, every photon - and for that matter, any physical two-level system - is immediately a qubit. In other words, qubits are abundant in nature and not very interesting by themselves. Also, a qubit alone is not entangled.
The interesting part is, what you can do with your qubit: Can you create a qubit in always the same state? Can you entangle a couple of qubits and protect their state from decoherence? Can you implement arbitrary unitary operations? The really interesting part here is the decoherence and operations question.
