Bunching-induced optical nonlinearity and instability in cold atoms [Invited]

Area of Science:

• Atomic Physics
• Nonlinear Optics
• Quantum Optics

Background:

• Cold atom ensembles are crucial for quantum technologies.
• Nonlinear optical processes typically require high light intensities.
• Controlling atomic states with light is key for quantum information processing.

Purpose of the Study:

• To report a novel nonlinear optical process in cold atoms at low light levels.
• To characterize the nonlinear optical response and its associated phenomena.
• To explore the potential of this process for atomic state manipulation and diagnostics.

Main Methods:

• Utilizing a cloud of cold atoms interacting with incident optical fields.
• Simultaneously employing polarization, cooling, and spatial organization of atoms.
• Measuring nonlinear optical properties, including effective susceptibility and Bragg scattering.

Main Results:

• Observed an extremely large effective fifth-order nonlinear susceptibility (χ(⁵) = 7.6 × 10⁻¹⁵ (m/V)⁴).
• Demonstrated efficient Bragg scattering via six-wave mixing, slow group velocities (∼ c/10⁵), and enhanced atomic coherence times (> 100 μs).
• Observed an optical instability generating new light beams and controllable transverse optical patterns at low intensities (∼ 1 mW/cm²).

Conclusions:

• The reported nonlinear optical process offers a new pathway for efficient light-matter interactions in cold atoms.
• The sensitivity to atomic temperature presents a novel method for in-situ monitoring of atomic momentum distribution in optical lattices.
• The observed optical instability and pattern formation open avenues for novel light generation and control techniques.