Helium in chirped laser fields as a time-asymmetric atomic switch

Area of Science:

• Atomic Physics
• Quantum Optics
• Laser Spectroscopy

Background:

• Helium atom's ground and doubly excited P-states can be coupled by a weak linearly polarized laser.
• Exceptional points (EPs) in the spectrum of dressed atoms offer unique phenomena.

Purpose of the Study:

• To investigate time-asymmetric state exchange in helium atoms using chirped laser pulses encircling an exceptional point.
• To explore the potential of this phenomenon as a controllable atomic switch.

Main Methods:

• Utilizing chirped laser pulses to interact with the helium atom.
• Tuning laser parameters to encircle exceptional points in the dressed atom spectrum.
• Analyzing the population dynamics of atomic states based on chirp direction and contour choice.

Main Results:

• A time-asymmetric state exchange is observed: negative chirp populates auto-ionization states, while positive chirp leaves the atom in the ground state.
• The phenomenon is highly sensitive to the chosen closed contour around the exceptional point.
• Optimal asymmetric switching occurs for larger contours encircling the EP.

Conclusions:

• A controllable time-asymmetric atomic switch based on laser-induced state exchange is demonstrated.
• The sensitivity to contour choice suggests a tunable mechanism for quantum control.
• This work opens avenues for novel applications in quantum information and control systems.