Fundamental quantum limit to the multiphoton absorption rate for monochromatic light

Area of Science:

• Quantum optics
• Atomic and molecular physics
• Laser physics

Background:

• Multiphoton absorption is a fundamental process in quantum optics.
• Understanding the factors influencing absorption rates is crucial for applications in spectroscopy and laser technology.
• Previous research explored quantum states for potential absorption enhancement.

Purpose of the Study:

• To determine the theoretical upper bound of the multiphoton absorption rate.
• To investigate whether quantum states of light can enhance multiphoton absorption beyond classical limits.
• To analyze the role of photon number, momentum, and polarization in multiphoton absorption.

Main Methods:

• Theoretical analysis of the local multiphoton absorption rate.
• Consideration of arbitrary quantum states of monochromatic light.
• Comparison of absorption rates for quantum states versus coherent fields.

Main Results:

• The local multiphoton absorption rate has a theoretical upper bound.
• This upper bound is achievable using coherent fields.
• Quantum states, including those with momentum entanglement, do not surpass the absorption rate of coherent fields.

Conclusions:

• Coherent fields represent the optimal state for maximizing multiphoton absorption.
• Momentum entanglement does not provide a quantum enhancement for multiphoton absorption rates.
• The findings clarify the role of quantum properties in light-matter interactions.