Macroscopic Quantum Superposition in a Three-Josephson-Junction Loop

Caspar H. van der Wal, A.C.J. ter Haar, F.K. Wilhelm, R.N. Schouten, C.J.P.M. Harmans, T.P. Orlando, Seth Lloyd, J.E. Mooij


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We present microwave-spectroscopy experiments on two quantum levels of a superconducting loop with three Josephson junctions. The level separation between the ground state and first excited state shows an anti-crossing where two classical persistent-current states with opposite polarity are degenerate. This is evidence for symmetric and antisymmetric quantum superpositions of two macroscopic states; the classical states have persistent currents of 0.5 µA and correspond to the center-of-mass motion of millions of Cooper pairs. A study of the thermal occupancies of the two quantum levels shows that the loop is at low temperatures in a non-equilibrium state.
Originele taal-2English
UitgeverijUniversity of Groningen, The Zernike Institute for Advanced Materials
Aantal pagina's10
StatusPublished - 2001

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