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Landau - Zener interferometry in multilevel systems

Mikhail Kiselev, ICTP Trieste

22.01.2016 at 09:00 

We propose a universal approach to the Landau-Zener (LZ) problem in a multilevel system. The problem is   formulated in terms of generators of SU(N) algebra and maps the Hamiltonian onto the effective anisotropic pseudospin (N-1)/2 model. The vector Bloch equation for the density matrix describing the temporal evolution of  the multilevel crossing problem is derived and solved analytically for two generic cases: i) three-level crossing  problem representing a minimal model for a LZ interferometer and ii) four-level crossing problem corresponding to  a minimal model of coupled interferometers. It is shown that the analytic solution of the Bloch equation is in  excellent quantitative agreement with the numerical solution of the Schroedinger equation for the 3- and 4- level  crossing problems. The solution demonstrates oscillation patterns which radically differ from the standard patterns for the two-level Landau- Zener problem: "beats" when the dwell time in the interferometer is smaller compared to a tunnel time and "steps" in the opposite limit. The possibilities of the experimental realization of LZ  interferometers in the system of coupled quantum dots, Josephson charge qubits and in two-well traps for cold   gases are discussed.

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