Quantum Entanglement Kevin Zielnicki Advisor : Paul G. Kwiat Physics - PowerPoint PPT Presentation

Quantum Entanglement Kevin Zielnicki Advisor : Paul G. Kwiat Physics 403 talk : April 17, 2012

This talk has three sections: I'll start with a basic introduction to entanglement  Introduction  How to make entanglement  Quantum information application: teleportation

Entanglement is a feature of compound quantum systems Ψ AB = φ 1 A φ 2 B  States that can be written are separable  States that cannot be written this way are entangled Example: the Bell states & are inseparable No solution! Measurement outcomes are random and correlated

What's so special about entanglement?  Classical things can be random and correlated, too…  … but not entangled! How is this different from an entangled state?  Each marble has a defined color from the beginning (local hidden variable)  The processes are distinguishable in principle  There is no conjugate measurement basis Entangled systems give random and correlated measurement outcomes in every measurement basis!

How do we make these entangled states in practice?  Introduction  How to make entanglement  Quantum information application: teleportation

Spontaneous parametric down-conversion Type I SPDC: • Intense laser pumps nonlinear crystal • Each pump photon has a small amplitude to downconvert o e o Source: David Guzman, Universidad de los Andes

Spontaneous parametric down-conversion  polarization-entanglement H-polarized V-polarized V  ° H HH  VV Crystal #1: Crystal #2 (at 90 ): superposition  polarization entanglement 1     i i V e H  HH e VV [1] Kwiat et al., PRA , 60 , R773 (1999)

Entanglement plays an important role in quantum communication and computation  Introduction  How to make entanglement  Quantum information application: teleportation

Alice and Bob share an entangled state; Alice also has an unknown state Bob Alice Bell-state measurement Classical Communication Unitary Transformation

Summary  Entangled systems cannot be completely described independently  Entanglement is a type of correlation between quantum systems that is stronger than any classical correlation  Entanglement is fairly easy to create in the lab  Entanglement plays a central role in quantum information applications