Experimental demonstration of free-space two-photon interference.

Area of Science:

• Quantum Physics
• Quantum Information Processing
• Quantum Optics

Background:

• Quantum interference is fundamental to quantum physics and essential for quantum information processing.
• Photon interference via fiber channels is common, but free-space implementation is limited by atmospheric turbulence.

Purpose of the Study:

• To experimentally demonstrate Hong-Ou-Mandel interference using photons transmitted through free-space channels.
• To assess the feasibility of free-space quantum interference for quantum information applications.

Main Methods:

• Utilized two photon sources: spontaneous parametric down-conversion (SPDC) and weak coherent states.
• Experimentally implemented Hong-Ou-Mandel interference for photons transmitted via free-space.
• Measured interference visibility.

Main Results:

• Achieved a visibility of 0.744 ± 0.013 for photons from SPDC, surpassing the classical limit of 0.5.
• Demonstrated that quantum properties of photons are preserved after free-space transmission.
• Confirmed the feasibility of free-space quantum interference.

Conclusions:

• Free-space quantum interference, specifically Hong-Ou-Mandel interference, is achievable despite atmospheric challenges.
• The preservation of quantum properties in free-space transmission opens avenues for quantum networks and processing.
• This work highlights the potential of free-space quantum interference for future quantum technologies.