Multipassage Landau-Zener tunneling oscillations in the dual dressing of atomic qubits.

The application of nonresonant electromagnetic fields, a technique known as 'dressing', provides critical control over the properties of fundamental quantum systems. We investigate the time evolution of a dressed-atom coherent spin ensemble, effectively representing a qubit, driven by a non-resonant electromagnetic field with two components, one along the quantisation static magnetic field and the other one orthogonal to it. While this second component produces a Larmor precession of the spin, the longitudinal dressing modifies the instantaneous field value, leading to a frequency modulated temporal evolution of the spin. This dual-dressing configuration represents an extension of the Landau-Zener multipassage interferometry in the presence of an additional dressing field controlling the tunneling process by its amplitude and phase. Our measurement of the qubit coherence introduces additional features to the transition probability readout of standard interferometry. The coherence time evolution is characterized by oscillations at several frequencies, each of them produced by a different quantum contribution. Such frequency description introduces a new picture of the qubit multipassage evolution. Our tuning-dressed configuration expands the toolbox for quantum state manipulation and quantum control applications. The experiments are performed in rubidium and caesium atomic magnetometers, confined in a magneto-optical trap and in a vapour cell, respectively. Static fields in the μT range and kHz oscillating fields with large Rabi frequencies are applied. Because the present low-frequency dressing operation does not fall within the standard Floquet engineering paradigm based on the high-frequency expansion, we develop an ad-hoc dressing perturbation treatment. Numerical simulations support the adiabatic and non-adiabatic qubit evolution.