Hong-Ou-Mandel Effect
Two identical photons enter a beamsplitter — they always exit together
Controls
Delay Δt:
0 fs
Distinguishability:
0%
Coherence time τ_c:
100 fs
Auto-Scan Δt
Reset
Coincidence Rate
P_coinc = ½[1 − |g(Δt)|²·(1−d)]
C12
—
HOM
—
At Δt=0:
Perfect dip — coincidences vanish
Dip depth = 1−d (distinguishability d)
Quantum Paths
Four amplitude paths through BS:
• RR: both reflect → |1,1⟩_out
• TT: both transmit → |1,1⟩_out
• RT: one each → |2,0⟩_out
• TR: one each → |0,2⟩_out
RR amplitude = +½
TT amplitude = −½ (reflection phase)
→ Destructive interference!
Both photons exit same port.