Metastable States of Josepshon Vortices:
Thermal Processes and Quantum Effects

A. Wallraff, A. Kemp, Yu. Koval, and A. V. Ustinov

Physikalisches Institut III,
Universitaet Erlangen-Nuernberg, D-91058 Erlangen

M. V. Fistul

MPI fŸr Physik komplexer Systeme, Dresden

We experimentally study the dynamics of a single Josephson vortex in a
tilted periodic potential.  In the presence of a bias current applied
uniformly to a long Josephson junction, metastable vortex-states are
induced by the interaction of the vortex with an artificially formed
inhomogeneity in the junction, or by shaping a junction subject to a
small external magnetic field [1].  At high temperatures, we observe
the thermal escape of the vortex out of the metastable state.  As
temperature and damping is reduced, the macroscopic quantum properties
of Josephson vortices, such as energy level quantization and quantum
tunneling, are expected to manifest themselves [2,3].  We report on our
current experimental work to observe these effects.  Our interest in
this macroscopic quantum system is related to the possibility of
using quantum states of Josephson vortices for performing quantum
computation.  We have suggested that a vortex trapped in a double-well
potential in a narrow long junction can be used as a scalable and
well-controllable qubit [1].


[1] A. Wallraff et al. , J. Low Temp.  Phys. J. Low Temp. Phys. 188,
543 (2000).
[2] T. Kato and M. Imada, J. Phys.  Soc.  Japan 65, 2963 (1996).
[3] A. Shnirman, E. Ben-Jacob, and B. Malomed, Phys.  Rev.  B 56,
14677 (1997).