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CeNS Colloquium

Place: Kleiner Physik-Hörsaal, Geschwister-Scholl-Platz
Date: 28.05.10, Time: 15:30 h

Manipulation of microscopic two-level systems by using a superconducting circuit

Prof. Alexey Ustinov
Karlsruher Institut für Technologie (KIT)

Experiments with quantized Josephson plasma oscillations in tunnel junctions display signatures of coherent coupling to individual microscopic defects acting as two-level systems (TLSs). These defects manifest themselves by avoided level crossings in microwave spectroscopy data reflecting the dependence of the Josephson plasma frequency on the current flowing through the junction. They are currently understood as nanoscale dipole states emerging from metastable lattice configurations in amorphous dielectrics forming the tunnel barrier of the Josephson junction. Such dipolar TLSs couple to the electrical field inside the junction which oscillates at the Josephson plasma frequency. I will present our recent experiments in which we use a Josephson junction for manipulating the quantum state of a single TLS. These experiments allow to directly measure the energy relaxation T1 and dephasing T2 times of an individual microscopic dipole-like TLS. Driving Rabi oscillations of the junction tuned close to a resonance with TLS leads to the observation of true 4-level dynamics [1]. The multi-photon spectroscopy allows for direct probing of hybridized states in the combined junction-defect coupled quantum system [2]. Moreover, by tuning the junction plasma frequency back and forth one can create and manipulate entanglement between multiple microscopic TLSs.

 

References:
[1] J. Lisenfeld, C. Müller, J. H. Cole, A. Lukashenko, A. Shnirman, and A.V. Ustinov, Phys. Rev. B 81, 100511 (2010).
[2] P. Bushev, C. Müller, J. Lisenfeld, J. H. Cole, A. Lukashenko, A. Shnirman, and A.V. Ustinov, arXiv:1005.0773.