The wave of a photon/Other experiments

Hong–Ou–Mandel Interferometer

Hong–Ou–Mandel diagram

The Hong-Ou-Mandel interferometer is a variant of the Mach-Zehnder interferometer in which two simultaneous photons are compared. A 351 nm laser radiates a KDP crystal, which because of SPDC emits now and then two entangled photons of about 702 nm. The KDP is propably a type I, in which both photons have the same polarization and the same phase. Both waves are mixed in a 50% reflecting mirror, filtered by a bandpass interference filter IF and detected with a coincidence of 7.2 ns.

It is supposed that this beam splitter is a glass plate with reflector on one side, causing (only) the reflection from the normal input having a phase shift of π. All other have no phase shift. At the detectors the waves are: I_u = 0.5sin(π+ωt+φ/2) + 0.5sinαsin(ωt-φ/2) and I_l = 0.5sin(ωt+φ/2) + 0.5sinαsin(ωt-φ/2). With an ideal bandwidth filter d = Δω/ω, the probability is calculated:

P_u = 0.5 - 0.5cos(4πΔx/λ) sin(πd(2k+2Δx/λ)) / πd(2k+2Δx/λ) and P_l = 0.5 + 0.5cos(4πΔx/λ) sin(πd(2k+2Δx/λ)) / πd(2k+2Δx/λ)

These formula predicts the result of the measurement if the cosine term is ignored and k = 0. Then the formula will be:

P_u = 0.5 - 0.5sin(πd2Δx/λ) / πd2Δx/λ

P_l = 0.5 + 0.5sin(πd2Δx/λ) / πd2Δx/λ

coincident: P = P_u * P_l

Beam spliter displacement compared to norm

In the experiment ω = 2πc/702nm = 2.7 10¹⁵. The bandwidth filter is 3 10¹³, d = 3 10¹³ / 2.7 10¹⁵ = 0.011. Then FWHM = 113 μm.