QUROPE Quantum Information Processing and Communication in Europe

The Karlsruhe groups of A. Ustinov and A. Shnirman (KTA) have demonstrated a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. The method allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. The group has applied this method to perform the first measurement of the temperature dependence of TLS coherence. The energy relaxation time T1 is found to decrease quadratically with temperature for the two TLSs studied in this work, while their dephasing time measured in Ramsey and spin-echo experiments is found to be T1 limited at all temperatures.

Measuring the Temperature Dependence of Individual Two-Level Systems by Direct Coherent Control
J. Lisenfeld, C. Müller, J. H. Cole, P. Bushev, A. Lukashenko, A. Shnirman, and A. V. Ustinov
Phys. Rev. Lett. 105, 230504 (2010)
http://link.aps.org/doi/10.1103/PhysRevLett.105.230504