We study the novel nonlinear phenomena that emerge in a charge qubit due to the interplay between a strong microwave flux drive and a periodic Josephson potential. We first analyse the system in terms of the linear Landau–Zener–Stückelberg model, and show its inadequacy in a periodic system with several Landau–Zener crossings within a drive period. Experimentally, we probe the quasienergy level...

We report time-resolved measurements of Landau-Zener tunneling of Bose-Einstein condensates in accelerated optical lattices, clearly resolving the steplike time dependence of the band populations. Using different experimental protocols we were able to measure the tunneling probability both in the adiabatic and in the diabatic bases of the system. We also experimentally determine the contributio...

We propose a new type of interferometry, based on geometric phases accumulated by a periodically driven two-level system undergoing multiple Landau-Zener transitions. As a specific example, we study its implementation in a superconducting charge pump. We find that interference patterns appear as a function of the pumping frequency and the phase bias, and clearly manifest themselves in the pumpe...

–We investigate spin-dependent interband tunnelling in a ferromagnetic (Ga,Mn)As/ GaAs Zener diode. The ferromagnetic pn-junction is fabricated with a Mn-doped p-type GaAs layer on top of a nonmagnetic n-type GaAs substrate. When both sides of the junction are heavily doped, a large magnetic-field–dependent tunnelling effect can be seen at low temperatures in the measured current-voltage (I-V )...

–We investigate spin-dependent interband tunnelling in a ferromagnetic (Ga,Mn)As/ GaAs Zener diode. The ferromagnetic pn-junction is fabricated with a Mn-doped p-type GaAs layer on top of a nonmagnetic n-type GaAs substrate. When both sides of the junction are heavily doped, a large magnetic-field–dependent tunnelling effect can be seen at low temperatures in the measured current-voltage (I-V )...

Laser-induced optical breakdown by femtosecond pulses is extraordinarily precise when the energy is near threshold. Despite numerous applications, the basis for this deterministic nature has not been determined. We present experiments that shed light on the basic mechanisms of light-matter interactions in this regime, which we term "optics at critical intensity." We find that the remarkably sha...