Director: Pertti Hakonen
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00076 AALTO
FINLAND

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# Physics and applications of mesoscopic Josephson junctions

Mesoscopic Josephson junctions provide an unique opportunity to construct ultra sensitive quantum detectors and amplifiers. These devices are important when performing single shot read-out of quantum bits (qubits) or making quantum measurements a la quantum optics style. The ultimate goal is to develop phase sensitive quantum amplifiers, parametric amplifiers that would allow for quantum non-demolition measurements.

Our quantum amplifiers employ the band model of the Josephson junction, either in a single junction case (BOT) or in a double junction case (L-SET and C-SET).

Below, the Hamiltonian describing a superconducting SET:

$\mathcal{H}=E_{CP}\left(\frac{\partial}{i\partial\theta}-n_g\right)-E_J\cos\phi/2\cos\theta$

 Energy bands (eigenenergies of the Hamiltonian above) of a superconducting SET for different EJ/EC on the plane spanned by the "classical variables", the gate charge qg and the sum phase φ. The quantum variables are the difference phase θ and island charge q=di/dθ.