Quantum optics of lossy asymmetric beam splitters

Area of Science:

• Quantum optics
• Photonics
• Quantum information science

Background:

• Quantum interference is fundamental to quantum computation and information processing.
• Passive optical circuits, like beam splitters, are key components in photonic quantum technologies.
• Losses in optical systems typically degrade quantum effects, posing a challenge for device performance.

Purpose of the Study:

• To theoretically investigate quantum interference of single photons at a lossy asymmetric beam splitter.
• To explore the role of non-unitary scattering matrices and their constraints due to losses.
• To determine if losses can be leveraged to enhance the tunability of quantum interference.

Main Methods:

• Theoretical analysis using the noise operator formalism.
• Investigation of a lossy asymmetric beam splitter as the most general passive 2x2 optical circuit.
• Examination of the constraints imposed by non-unitary scattering matrices in the presence of loss.

Main Results:

• Losses in the beam splitter introduce a non-unitary scattering matrix with specific constraints.
• The presence of loss provides a new degree of freedom for tuning quantum interference.
• Tunability achieved with lossy beam splitters exceeds that of lossless counterparts.

Conclusions:

• Losses in passive optical circuits can be beneficial for controlling quantum interference.
• This work provides theoretical support for experimental demonstrations of programmable quantum interference.
• The findings are relevant for multimodal systems like scattering media and multimode fibers.