Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: TR: Quantum Coherence and Quantum Information Systems 2 (jointly with MA and HL)

TT 34.9: Talk

Wednesday, March 16, 2011, 16:30–16:45, HSZ 03

Measuring the temperature dependence of individual two-level systems by direct coherent control — •Jürgen Lisenfeld^1,4, Clemens Müller^2,4, Jared H. Cole^3,4, Pavel Bushev^1,4, Alexandr Lukashenko^1,4, Alexander Shnirman^2,4, and Alexey V. Ustinov^1,4 — ¹Physikalisches Institut, Karlsruhe Institute of Technology, Karlsruhe, Germany — ²Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, Karlsruhe, Germany — ³Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology, Karlsruhe, Germany — ⁴DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, Karlsruhe, Germany

We demonstrate a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. It allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. We apply this method to measure the temperature dependence of TLS coherence for the first time. 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.