Ultrafast quantum control of atomic excited states via interferometric two-photon Rabi oscillations.

Quantum-state manipulation through coherent interaction with a radiation field is a fundamental process with broad implications in quantum optics and quantum information processing. However, current quantum control methods are limited by their operation at Rabi frequencies below the gigahertz range, which restricts their applicability to systems with long coherence times. To overcome this limitation, alternative approaches utilizing ultrafast driving lasers have garnered great interest. In this work, we demonstrate two-photon Rabi oscillations in the excited states of argon operating at terahertz frequencies driven by ultrafast laser pulses. Leveraging quantum-path interferometry, we are able to measure and manipulate both the amplitudes and phases of the transition dipoles by exploiting the intensity and polarization state of the driving laser. This precise control enables femtosecond population transfer and coherent accumulation of geometric phase. Our findings provide valuable insights into the all-optical manipulation of extreme-ultraviolet radiations and demonstrate the possibility of ultrafast quantum control through interferometric multiphoton transitions. Quantum control with coherent radiation fields typically operate at Rabi frequencies below the GHz, limiting the applicability of this scheme to systems with long coherence times. Via quantum path intereferometry, the authors overcome this limitation and control two-photon Rabi oscillations between excited states driven by femtosecond laser pulses. [ABSTRACT FROM AUTHOR]