Regensburg 2010 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 23: TR: Quantum Coherence and Quantum Information Systems 2
TT 23.3: Talk
Wednesday, March 24, 2010, 14:30–14:45, H18
Josephson quartic oscillator as a superconducting phase qubit — •Alexander Zorin1 and Fabio Chiarello2 — 1Physikalisch-Technische Bundesanstalt, 38116 Braunschweig, Germany — 2Istituto di Fotonica e Nanotecnologie, CNR, 00156 Rome, Italy
Due to interplay between the cosine Josephson potential and parabolic magnetic-energy potential the radio-frequency SQUID with the screening parameter value βL ≡ (2π/Φ0)LIc ≈ 1 presents an oscillator circuit which energy well can dramatically change its shape. Ultimately, the magnetic flux bias of half flux quantum Φe=Φ0/2 leads to the quartic polynomial shape of the well and, therefore, to significant anharmonicity of oscillations (> 30%). We show that the two lowest eigenstates in this symmetric global minimum perfectly suit for designing the qubit which is inherently insensitive to the charge variable, always biased in the optimal point and allows efficient dispersive and bifurcation-based readouts. Moreover, in the case of a double-SQUID configuration (dc SQUID instead of a single junction) the transition frequency in this Josephson phase qubit can be easy tuned within an appreciable range allowing variable qubit-qubit and qubit-resonator couplings.