Gaussian versus Non-Gaussian Filtering of Phase-Insensitive Nonclassicality.

Area of Science:

• Quantum optics
• Quantum information theory

Background:

• Measures of quantum properties are crucial for distinguishing quantum and classical systems.
• Phase-space functions, like the Glauber-Sudarshan P function, are vital for characterizing quantum states.
• Quantifying nonclassical effects is essential for developing quantum technologies.

Purpose of the Study:

• To compare two classes of bosonic phase-space functions for their ability to detect nonclassical effects in light.
• To investigate the role of filtering (Gaussian vs. non-Gaussian) on the P function in revealing quantum properties.
• To develop and experimentally demonstrate a method for directly sampling these phase-space functions.

Main Methods:

• Utilized balanced homodyne measurements to directly sample phase-space functions.
• Employed Gaussian filtering to obtain s-parametrized quasiprobabilities.
• Applied non-Gaussian filtering to generate regularized nonclassicality quasiprobabilities.
• Experimentally tested the method on heralded single- and two-photon states.

Main Results:

• Directly sampled s-parametrized quasiprobabilities showed non-negativity below 0.5 detection efficiency.
• Non-Gaussian filtered quasiprobabilities exhibited significant negativities, indicating nonclassical effects.
• The proposed sampling method overcomes previous limitations in handling optical phase data.

Conclusions:

• Non-Gaussian filtered quasiprobabilities are more robust in uncovering nonclassical effects of light at low detection efficiencies.
• The developed direct sampling technique provides a practical approach for characterizing quantum states.
• This research advances the understanding and quantification of quantum resources for quantum technologies.