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Zeitschrift für Naturforschung A

On Some Aspects of an Hg Based EPR Experiment

Thomas Walther, Edward S. Fry

Published Feb 1, 1997• 3 citations
Publisher

Abstract

Abstract An experimental realization of Bohm's spin-1/2 EPR gedanken-experiment is possible using the spin-1/2 nuclei of the isotope 199 Hg. The dissociation of dimers of the 199 Hg 2 isotopomer, using a spectroscopically selective stimulated Raman process, leads to the generation of an entangled state between the two 199 Hg atoms. The measurement of nuclear spin correlations between the two atoms in this entangled state is achieved by detection of the atoms using a spin state selective two photon excitation-ionization scheme. The experiment will not only close the detector efficiency loophole, but in addition will permit enforcement of the locality condition. Effects of imperfect analyzers will also be discussed.

DOI
10.1515/zna-1997-1-208

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arXiv:2507.22166•Jan 1, 2005•6 citations
Abstract An experimental realization of Bohm's spin-1/2 EPR gedanken-experiment is possible using the spin-1/2 nuclei of the isotope 199 Hg. The dissociation of dimers of the 199 Hg 2 isotopomer, using a spectroscopically selective stimulated Raman process, leads to the generation of an entangled state between the two 199 Hg atoms. The measurement of nuclear spin correlations between the two atoms in this entangled state is achieved by detection of the atoms using a spin state selective two photon excitation-ionization scheme. The experiment will not only close the detector efficiency loophole, but in addition will permit enforcement of the locality condition. Effects of imperfect analyzers will also be discussed.
A proposal for an experimental realization of Bohm's spin-1/2 particle version of the Einstein-Podolsky-Rosen experiment is described. Two 199Hg^{199}\mathrm{Hg}199Hg atoms, each with nuclear spin 1/2, are produced in an entangled state with total nuclear spin zero. Such a state is obtained by dissociation of dimers of the 199Hg2^{199}\mathrm{Hg}_{2}199Hg2​ isotopomer using a spectroscopically selective stimulated Raman process. The measurement of nuclear spin correlations between the two atoms in this entangled state is achieved by detection of the atoms using a spin state selective two-photon excitation-ionization scheme. The experiment will not only close the detector efficiency loophole, but in addition will permit enforcement of the locality condition.
All previous experimental tests of Bell inequalities have required additional assumptions. The strong Bell inequalities (i.e. those requiring no additional assumptions) have never been tested. An experiment has been designed that can, for the first time, provide a definitive test of the strong Bell inequalities. Not only will the detector efficiency loophole be closed; but the locality condition will also be rigorously enforced. The experiment involves producing two Hg-199 atoms by a resonant Raman dissociation of a mercury dimer ((199)Hg2) that is in an electronic and nuclear spin singlet state. Bell inequalities can be tested by measuring angular momentum correlations between the spin one-half nuclei of the two Hg-199 atoms. The method used to make these latter measurements will be described.
The status of our experimental realization of Bohm’s spin-1/2 particle version of the Einstein-Podolsky-Rosen gedankenexperiment is discussed. This new experiment provides a definitive test of the, as yet, untested strong Bell inequalities. It closes the two widely recognized loopholes associated with previous experiments, and has the interesting new feature that the entangled state exists for milliseconds rather than nanoseconds. The spin one-half particles are two 199 Hg atoms in an entangled nuclear spin state with total nuclear spin zero. Measurement of the nuclear spin correlation is achieved by detection of each atom using a spin state selective two photon excitation-ionization scheme.
Most experimental tests of Bell inequalities have involved measurements of correlations between two photons. One of the first definitive experiments involved the linear polarization correlation between two photons in an atomic cascade of 200 Hg. That experiment is discussed in depth in this paper. The form of the initial state density matrix was a critical part of that experiment; and the experimental and theoretical determination of the density matrix, including finite solid-angle effects is discussed. However, all Bell inequality experiments to date have two widely recognized loopholes, detector efficiency and locality. This paper concludes with a very brief description of an experiment that will close both of these loopholes. In contrast to existing experiments with photons, this new test involves spin correlations between the nuclei of two 199 Hg atoms; it is an exact experimental realization of Bohm's version of the Einstein-Podolsky-Rosen gedankenexperiment.
We present recent progress in the implementation of experimental realization of a loophole-free test of Bell inequalities for entangled 111Cd atoms. The experimental approach is a modified version of the proposal of FRY and co-workers (Phys. Rev. A 52(6), 1995, p. 4381) for the realization of Bohm’s 1/2-spin particle version of the Einstein–Podolsky–Rosen (E-P-R) experiment and is based on the production of entangled atoms by photodissociation of the 111Cd2 isotopologue in a supersonic expansion beam using the spectroscopically selective stimulated Raman process.
In 1935 Einstein, Podolsky and Rosen used the assumption of local realism to conclude in a Gedankenexperiment with two entangled particles that quantum mechanics is not complete. For this reason EPR motivated an extension of quantum mechanics by so-called local hidden variables. Based on this idea in 1964 Bell constructed a mathematical inequality whereby experimental tests could distinguish between quantum mechanics and local-realistic theories. Many experiments have since been done that are consistent with quantum mechanics, disproving the concept of local realism. But all these tests suffered from loopholes allowing a local-realistic explanation of the experimental observations by exploiting either the low detector efficiency or the fact that the detected particles were not observed space-like separated. In this context, of special interest is entanglement between different quantum objects like atoms and photons, because it allows one to entangle distant atoms by the interference of photons. The resulting space-like separation together with the almost perfect detection efficiency of the atoms allows a first loophole-free test of Bell's inequality. The primary goal of the present thesis is the experimental realization of entanglement between a single localized atom and a single spontaneously emitted photon at a wavelength suitable for the transport over long distances. In the experiment a single optically trapped Rb87 atom is excited to a state which has two selected decay channels. In the following spontaneous decay a photon is emitted coherently with equal probability into both decay channels. This accounts for perfect correlations between the polarization state of the emitted photon and the Zeeman state of the atom after spontaneous decay. Because these decay channels are spectrally and in all other degrees of freedom indistinguishable, the spin state of the atom is entangled with the polarization state of the photon. To verify entanglement, appropriate correlation measurements in complementary bases of the photon polarization and the internal quantum state of the atom are performed. It is shown, that the generated atom-photon state yields an entanglement fidelity of 0.82. The experimental results of this work mark an important step towards the generation of entanglement between space-like separated atoms for a first loophole-free test of Bell's inequality. Furthermore entanglement between a single atom and a single photon is an important tool for new quantum communication and information applications, e.g. the remote state preparation of a single atom over large distances.