Coherence properties of spontaneous parametric down-conversion pumped by a multi-mode cw diode laser

Area of Science:

• Quantum Optics
• Laser Physics

Background:

• Spontaneous parametric down-conversion (SPDC) is a key process for generating entangled photon pairs.
• Understanding the coherence properties of these photon pairs is crucial for quantum information applications.
• Multi-mode continuous-wave (cw) diode lasers are practical pump sources, but their coherence characteristics can influence generated photons.

Purpose of the Study:

• To investigate the coherence properties of photon pairs generated by SPDC pumped by a multi-mode cw diode laser.
• To analyze the influence of input photon delays on biphoton interference patterns.
• To explore the potential of these engineered entangled photon sources.

Main Methods:

• Utilizing a Mach-Zehnder interferometer to study photon pair coherence.
• Introducing each photon of the pair into separate input ports of the interferometer.
• Employing a two-photon detector at an output port to measure biphoton coherence.

Main Results:

• Observed periodic recurrence of the biphoton de Broglie wave packet when photons enter simultaneously, mirroring pump laser coherence.
• Demonstrated that biphoton interference with non-zero input delays maintains periodic recurrence.
• Showed that wave packet shapes depend on both input and interferometer delays.

Conclusions:

• The coherence properties of SPDC photons are strongly linked to the pump laser's characteristics.
• Engineered entangled photon sources can be developed using diode laser-pumped SPDC.
• The observed wave packet dynamics offer insights for controlling and utilizing entangled photons in quantum technologies.