Quantum Eraser

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A Double-Slit Quantum Eraser Experiment

This web-page was created as an assignment for PHY 566, taught by Prof. Luis Orozco at Stony Brook University in the fall semester of 2002.

The following describes work done by S. P. Walborn, M. O. Terra Cunha, S. Padua, and C. H. Monken at the Universidade Federal de Minas Gerais in Brazil. Their work was published last March in Physical Review A, (65, 033818, 2002). The pdf version of the publication can be found here.

This experiment uses the phenomena of interference, produced by light incident on a double slit, to investigate the quantum mechanical principle of complementarity between the wave and particle characteristics of light. Using a special state of light, Walborn and his coworkers created an interference pattern, made a "which-way" measurement which destroyed the interference, and then erased the "which-way" marker, bringing the interference back. This experiment clearly displays the way in which nature is counterintuitive on the quantum scale and makes it clear that our ways of thinking based on our everyday experiences in the classical world are often completely inadequate to understand the quantum world.

Retrieved by DonEMitchell 07:02, 24 December 2012 (MST) from http://grad.physics.sunysb.edu/~amarch/

Einstein's Spooks and Bell's Theorem

by John G. Cramer
URL: http://www.npl.washington.edu/AV/altvw37.html

The Quantum Eraser

by John G. Cramer
URL: http://www.npl.washington.edu/AV/altvw90.html

A Do-It-Yourself Quantum Eraser

Note that this experiment actually does not require a quantum explanation. Classical electromagnetic theory can explain the result by reminding us that there is a real interaction of the fields with electrons in the polarizing filter . See e.g. the reference below:
Moreover, the 3-polarizers effect can be reproduced with microwaves (i.e. 'light' of long wavelength) using the appropriate experimental set-up. Once more, no quantum explanation is really necessary for this experiment...
The "punchline" is invalid because light of different polarization doesn't interfere even in classical E&M.
F. A. Torres-Ruiz1,2, G. Lima1,2, A. Delgado1,2, S. Pádua3, and C. Saavedra1,2,*
1Center for Optics and Photonics, Universidad de Concepción, Casilla 4016, Concepción, Chile
2Departamento de Fisica, Universidad de Concepción, Casilla 160-C, Concepción, Chile
3Departamento de Física, Universidade Federal de Minas Gerais, Caixa Postal 702, Belo Horizonte, MG 30123-970, Brazil

Received 1 October 2009; published 7 April 2010

We study and experimentally implement a double-slit quantum eraser in the presence of a controlled decoherence mechanism. A two-photon state, produced in a spontaneous parametric down-conversion process, is prepared in a maximally entangled polarization state. A birefringent double slit is illuminated by one of the down-converted photons, and it acts as a single-photon two-qubits controlled-not gate that couples the polarization with the transversal momentum of these photons. The other photon, which acts as a which-path marker, is sent through a Mach-Zehnder-like interferometer. When the interferometer is partially unbalanced, it behaves as a controlled source of decoherence for polarization states of down-converted photons. We show the transition from wavelike to particle-like behavior of the signal photons crossing the double slit as a function of the decoherence parameter, which depends on the length path difference at the interferometer.