Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 3: Quantum Coherence and Quantum Information Systems I

TT 3.3: Vortrag

Montag, 26. März 2007, 10:15–10:30, H20

Temperature Dependence of Rabi Oscillations in Phase Qubits — •Jürgen Lisenfeld, Alexandr Lukashenko, and Alexey Ustinov — Physikalisches Institut III, Universität Erlangen-Nürnberg

We will present measurements of Josephson phase qubits which feature the phase eigenstates of a Josephson junction placed in a superconducting loop and biased at a magnetic flux close to one flux quantum. The phase qubit is controlled by resonant microwaves and read out by a dc-SQUID measuring its flux state. We have measured Al-based phase qubits with SiNx shunting capacitors made at UCSB [1] and our similarly designed circuits fabricated at Hypres foundry using a standard Nb-based fabrication process with SiO₂ insulation. Rabi oscillations decay at half-life times that are about 100 ns and 5 ns, respectively.

We find that the oscillation amplitude as well as decay time do not decrease up to the temperature, at which the thermal energy k_BT becomes comparable to the energy level separation. The oscillations disappear at about 400 mK for the Al qubits and at about 700 mK for the qubits made of Nb. Our data point towards non-thermal origin of decoherence limiting the low-temperature performance of the phase qubits.

[1] M. Steffen, et al. Phys. Rev. Lett. 97, 050502 (2006)