The Hong–Ou–Mandel (HOM) effect is a hallmark phenomenon in quantum optics that reveals the quantum interference of indistinguishable photons. It occurs when two identical photons are sent into the two input ports of a beam splitter simultaneously.
What Happens:
- Classically, you’d expect a 50/50 chance that the photons exit separately or together.
- Quantum mechanically, if the photons are truly identical in all respects (wavelength, polarization, timing), they interfere destructively in such a way that both photons always exit together through the same port.
Key Consequence:
- You observe a “dip” in coincidence detection — known as the HOM dip — at the output detectors. This is strong evidence of the bosonic nature of photons and their tendency to “bunch” when indistinguishable.
Significance:
- It proves that photons are indistinguishable quantum particles.
- It plays a foundational role in quantum information processing, such as:
- Quantum teleportation
- Entanglement swapping
- Linear optical quantum computing
The HOM effect elegantly demonstrates how quantum interference defies classical expectations and is vital for building future quantum technologies.