# Dresden 2006 – wissenschaftliches Programm

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# TT: Tiefe Temperaturen

## TT 29: Transport: Quantum Coherence and Quantum Information Systems - Part 1

### TT 29.2: Vortrag

### Donnerstag, 30. März 2006, 10:00–10:15, HSZ 304

**Landau-Zener transitions in qubits and qubit-oscillator systems** — •Martijn Wubs^{1}, Keiji Saito^{2}, Sigmund Kohler^{1}, Yosuke Kayanuma^{3}, and Peter Hänggi^{1} — ^{1}Institut für Physik, Universität Augsburg, 86135 Augsburg — ^{2}Department of Physics, Graduate School of Science, University of Tokyo, Bunkyo-Ku, Tokyo 113-0033, Japan — ^{3}Department of Mathematical Science, Graduate School of Engineering, Osaka Prefecture University, Sakai 599-8531, Japan

In recent years, several solid-state systems have been identified as effective two-level systems, flux qubits and phase qubits for example. An advantage of these ‘artificial atoms’ is that they can be driven by gate voltages and external radiation fields. These systems are well suited for manipulation via Landau-Zener transitions. In this talk, we first discuss Landau-Zener transitions in a semiclassical model where both the energy difference and the interaction strength between the levels are controlled by external fields [1]. This model is a combination of the classic Landau-Zener and the Rabi problem. The probability of Landau-Zener transitions now depends sensitively on the amplitude, the frequency and the phase of the interaction. Secondly, motivated by recent advances in circuit QED, we studied Landau-Zener transitions in qubits that are strongly coupled to one or several quantum harmonic oscillators. We present exact calculations of some Landau-Zener transition probabilities also for these more complicated quantum systems. Moreover, we discuss the mapping of the quantum model onto the semiclassical model.

[1] M. Wubs, K. Saito, S. Kohler, Y. Kayanuma, P. Hänggi, New J. Phys. **7**, 218
(2005).