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Physical Review A

Comparing quantum and classical correlations in a quantum eraser

A. Gogo, W. D. Snyder, M. Beck

Published May 18, 2005• 38 citations
Publisher

Abstract

We have demonstrated the operation of a quantum eraser based on a polarization interferometer. Which-path information is erased not by modifying the interferometer apparatus, but instead by modifying the information obtained from measurements performed on a second beam, whose polarization is correlated with that of the interferometer beam. We compare the results obtained when the two beams are in an entangled state (quantum correlations) and in a mixed state (classical correlations). We find that classical correlations can mimic most, but not all, of the quantum-mechanical behavior.

DOI
10.1103/physreva.71.052103

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We have demonstrated the operation of a quantum eraser based on a polarization interferometer. Which-path information is erased not by modifying the interferometer apparatus, but instead by modifying the information obtained from measurements performed on a second beam, whose polarization is correlated with that of the interferometer beam. We compare the results obtained when the two beams are in an entangled state (quantum correlations) and in a mixed state (classical correlations). We find that classical correlations can mimic most, but not all, of the quantum-mechanical behavior.
The quantum eraser experiment was revisited, using entangled photons of visible light in a Hong-Ou-Handel type interferometer with a magnitude two orders higher than before in count rates. We introduced which-path information by polarization and subsequently erasied this information by means of polarizers in front of detectors. It was found that the visibility of the interference fringe is revived from 0% to 88% as the polarizers are changed from 0 ∘^{\circ}∘ to 45 ∘^{\circ}∘ .
We have observed an effect known as a quantum eraser, using a setup similar to one previously employed to demonstrate a violation of Bell's inequalities. In this effect, an interfering system is first rendered incoherent by making the alternate Feynman paths which contribute to the overall process distinguishable; with our apparatus this is achieved by placing a half wave plate in one arm of a Hong-Ou-Mandel interferometer so as to rotate the polarization of the light in that arm by 90\ifmmode^\circ\else\textdegree\fi{}. This adds information to the system, in that polarization is a new parameter which serves to label the path of a given photon, even after a recombining beam splitter. The quantum ``eraser'' removes this information from the state vector, after the output port of the interferometer, but in time to cause interference effects to reappear upon coincidence detection. For this purpose, we use two polarizers in front of our detectors. We present experimental results showing how the degree of erasure (which determines the visibility of the interference) depends on the relative orientation of the polarizers, along with theoretical curves. In addition, we show how this procedure may do more than merely erase, in that the act of ``pasting together'' two previously distinguishable paths can introduce a new relative phase between them.
In the conventional interpretation of quantum mechanics the interference of particles in a two-beam interferometer is closely related to the problem of which-way information. One of the mysteries of quantum mechanics relies on the assumption that the wavefunction of each photon propagates simultaneously along both classically allowed paths, and that interference arises as a consequence of the indistinguishability of those paths. Any attempt to obtain which-way information by putting individual labels on the photons in each pathway inevitably destroys interference. However, even in cases in which the photons carry which-way labels, it is possible to erase those labels after the particle has left the interferometer. The erasing process (partly or completely) destroys the which-way information, and thereby restores interference. This phenomenon is known as quantum erasing. Here we present a lecture demonstration experiment of quantum erasing based on a Mach–Zehnder interferometer operated with single photons.
We report a quantum-eraser experiment with frequency-entangled photon pairs generated by nondegenerate parametric down conversion. The relationship between which-path information and two-photon fringe visibility has been investigated by means of photon polarizations in a Hong-Ou-Mandel interferometer. Although photons are not of the same frequency and are not superposed at the beam splitter, the results of the experiment show the revival of the fringe pattern by removing the path information in the interferometer by means of polarizations in front of the detectors.
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.