Quantum Control by Few-Cycles Pulses: The Two-Level Problem.

Area of Science:

• Quantum dynamics
• Atomic and molecular physics
• Nonlinear optics

Background:

• Population transfer is crucial for quantum control.
• Short electromagnetic pulses (few-cycle) present challenges due to non-adiabatic effects.
• The rotating wave approximation often fails for such short pulses.

Purpose of the Study:

• To achieve ultrahigh-fidelity population transfer in two-state systems using minimal electromagnetic field cycles.
• To develop strategies effective even when the rotating wave approximation breaks down.
• To explore both adiabatic and non-adiabatic approaches for rapid quantum state manipulation.

Main Methods:

• Adiabatic passage based on adiabatic Floquet theory for 2.5 cycles.
• Implementing dynamics along an adiabatic trajectory.
• Deriving non-adiabatic strategies using shaped or chirped pulses.
• Extending the pi-pulse regime to two- or single-cycle pulses.
• Considering the physical constraint of a zero-area total field.

Main Results:

• Ultrahigh-fidelity population transfer achieved with as few as 2.5 cycles.
• Successful implementation of adiabatic passage dynamics.
• Development of novel non-adiabatic strategies for single- and two-cycle pulses.
• Demonstration of quantum control beyond the limits of the rotating wave approximation.

Conclusions:

• Effective population transfer is possible with very short electromagnetic pulses.
• Adiabatic Floquet theory provides a robust framework for few-cycle pulse dynamics.
• Novel pulse shaping and chirping techniques enable rapid quantum state control.