Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 2: Supraleitung: Dünne Schichten, Josephsonkontakte, SQUIDs I

TT 2.4: Vortrag

Montag, 11. März 2002, 11:15–11:30, H19

Quantum Dynamics of the Phase in Josephson Tunnel Junctions at Millikelvin Temperatures — •A. Wallraff¹, A. Lukashenko^1,2, C. Coqui¹, T. Duty¹, M. V. Fistul³, and A. V. Ustinov¹ — ¹Physikalisches Institut III, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen — ²B. I. Verkin Institute for Low Temperature Physics, Kharkov, Ukraine — ³MPI für Physik komplexer Systeme, Dresden

We experimentally study the dynamics of the phase difference in a small current-biased Josephson tunnel junction at low temperatures. The measured switching current distributions indicate the quantum tunneling of the phase at temperatures below a cross-over temperature of T^⋆ ≈ 300   mK. At temperatures T > T^⋆ the thermal activation of the phase is observed. We consider the presence of quantized energy levels in the well and discuss the effect of dissipation on the thermal activation process. Furthermore we have investigated the resonant escape of the phase in dependence on frequency and power of microwave radiation applied in the range from 10 to 40 GHz. Resonances have been oserved at the plasma frequency and its subharmonics. The experimental data are analyzed in the view of the energy-level structure of the Josephson junction. Our interest in macroscopic quantum effects is related to the possibility of using Josephson devices as basic elements for solid state quantum information processing.