Study of Quantum Interference Phenomena in Cold Atoms — from Reduction of the Light Speed to Quantum Entanglement 余怡德 清華大學物理系 陳應誠 廖彥安 林重維 陳韻文 蘇蓉容 邱馨瑩 潘冠錡 陳泳帆 蔡仁祥 楊致芸 劉昱辰 陳德鴻

Measure Light Speed in a Medium Detector Laser t Detector Laser t + td atoms l v  l / td

Chromatic dispersion

The index refraction of fused quartz.

Electromagnetically Induced Transparency (EIT) The Phenomenon of Electromagnetically Induced Transparency (EIT) probe laser coupling laser atoms

Quantum Interference + + + ....... = ....... ....... |3 Coupling |2 ....... = + + + Probe |1 path i path ii path iii ....... ....... Transition amplitudes: Ai Aii Aiii Transition probability of |1  |2 = | Ai + Aii + Aiii + ....... |2 EIT is the destructive interference between Ai , Aii , Aiii , .......  The probe absorption is suppressed.

Experimental Setup |g1 |g2 |e Coupling Laser Probe PD T z y x AOM Quadrupole Magnet T: trapping beam

Experimental Spectrum without the Coupling Laser

Experimental Spectrum in the Presence of the Coupling Laser

Ultrahigh Contrast near the Resonance

Group Velocity Predicted from the Experimental Data 吸收率 色散 折射率

Photon Switching by Quantum Interference Probe |1 |2 |3 |4 Coupling Switching

The Three-Fold Entangled State |1 |2 |3 |4 Coupling Switching Probe 50/50 BS where 1 or 0 in the | s, | p, and | f denotes presence or absence of the switching, probe, and fluorescence photons measured by the detectors. Requirements: OD  10 and   10-3.

Einstein-Podolsky-Rosen (EPR) Paradox QM:

Information Propagation Cannot Exceed c 1 S N Stern-Gerlach at t1 Stern-Gerlach at t2 L 2

Quantum Non-locality Down-conversion by a BBO crystal to generate two entangled photons along the intersecting directions of the cones.

Teleportation public communication EPR Source Bob Alice secure channel

Information Encoding and Decoding   ......... 1 ............... R x Bob Alice EPR1: EPR2: Information: