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

 States that can be written are separable  States that cannot be written this way are entangled

Measurement outcomes are random and correlated

Ψ AB = φ1 A φ2 B

Example: the Bell states & are inseparable No solution!

What's so special about entanglement?

 Classical things can be random and correlated, too…

Entangled systems give random and correlated measurement outcomes in every measurement basis!

 … but not entangled!

 Each marble has a defined color from the beginning

(local hidden variable)

 The processes are distinguishable in principle

 There is no conjugate measurement basis

How is this different from an entangled state?

How do we make these entangled states in practice?

 Introduction  How to make entanglement  Quantum information application: teleportation

Type I SPDC:

• Intense laser pumps nonlinear crystal
• Each pump photon has a small amplitude to downconvert

e

• Source: David Guzman, Universidad de los Andes

Spontaneous parametric down-conversion

H VV



V HH





i

V e H





i

HH e VV





Spontaneous parametric down-conversion  polarization-entanglement

[1] Kwiat et al., PRA, 60, R773 (1999)

Crystal #1: Crystal #2 (at 90 ):

superposition polarization entanglement1

 H-polarized V-polarized

°

Entanglement plays an important role in quantum communication and computation

 Introduction  How to make entanglement  Quantum information application: teleportation

Alice Bob Bell-state measurement Unitary Transformation Classical Communication

Alice and Bob share an entangled state; Alice also has an unknown state

Summary

 Entanglement is a type of correlation between quantum

systems that is stronger than any classical correlation

 Entangled systems cannot be completely described

independently

 Entanglement plays a central role in quantum information

applications

 Entanglement is fairly easy to create in the lab