Reversible inter-degree-of-freedom optical-coherence conversion via entropy swapping

Area of Science:

• Quantum optics
• Classical optics
• Information theory

Background:

• Optical fields possess entropy, quantifying fluctuations and coherence.
• Binary optical degrees-of-freedom (DoF), like polarization and spatial points, can each hold one bit of entropy.
• Coherence is a fundamental property of light, crucial for many optical phenomena and technologies.

Purpose of the Study:

• To demonstrate the reversible swapping of entropy between different optical degrees-of-freedom (DoF).
• To convert optical coherence between spatial and polarization states without energy loss.
• To show that maximizing spatial entropy can protect optical fields from phase scrambling.

Main Methods:

• Starting with a spatially coherent, unpolarized field, unitary operators were used to swap entropy.
• The coherence was converted from the spatial DoF to the polarization DoF, creating an incoherent, polarized field.
• The inverse unitary operator was applied to convert coherence back, retrieving the initial state.

Main Results:

• Successful reversible conversion of coherence between spatial and polarization DoFs was achieved.
• The intermediate state, where spatial coherence was converted to polarization, showed immunity to spatial phase scrambling.
• Retrieval of spatial coherence after the second conversion demonstrated the circumvention of phase scrambling effects.

Conclusions:

• Entropy can be reversibly swapped between optical degrees-of-freedom, interconverting coherence.
• This process allows for the manipulation of optical field properties, such as converting spatial coherence to polarization.
• The technique offers a method to protect optical fields from detrimental effects like spatial phase scrambling.