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arXiv:quant-ph/0310112 · Journal of Physics G Nuclear and Particle Physics

Testing quantum correlations with nuclear probes

S. Hamieh, H.J. Wörtche, Christian Bäumer, A. M. van den Berg, Dieter Frekers, Muhsin N. Harakeh, J. Heyse, Mátyás Hunyadi, M. A. de Huu, Christopher Polachic, S. Rakers, C. Rangacharyulu

Published Feb 20, 2004• 16 citations
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Abstract

We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In the first approach, we measured spin correlations of singlet-spin ( 1 S 0 ) proton pairs, which were generated in 1 H(d, 2 He) and 12 C(d, 2 He) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the 2 He singlet state and offered a 2π detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for these studies, despite limitations of a small data sample recorded during the feasibility studies.

DOI
10.1088/0954-3899/30/4/007

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We investigated the feasibility of quantum-correlation measurements in nuclear physics experiments. In the first approach, we measured spin correlations of singlet-spin ( 1 S 0 ) proton pairs, which were generated in 1 H(d, 2 He) and 12 C(d, 2 He) nuclear charge-exchange reactions. The experiment was optimized for a clean preparation of the 2 He singlet state and offered a 2π detection geometry for both protons in the exit channel. Our results confirm the effectiveness of the setup for these studies, despite limitations of a small data sample recorded during the feasibility studies.
Nuclear entanglement is a flagship in the interdisciplinary direction of nuclear physics and quantum information science. Spin entanglement, a special kind of nuclear entanglement, is ubiquitous in nuclear structures and dynamics. Based on the idea of quantum state tomography, the problem of experimental determination of spin entanglement of two-nucleon pure states is studied directly within the scope of nuclear physics. It is shown that the amount of spin entanglement can be obtained by measuring three spin polarizations of one nucleon in polarization experiments. The errors from imperfect preparation of nucleon pairs are also analyzed. This work not only complements the existing literature of nuclear entanglement but also provides new opportunities for nuclear physics with polarized particles.
We report the results of the first-time test of the local hidden variable theories (Bell-Clauser-Horne-Shimony-Holt) involving strongly interacting pairs of massive spin 1/21/21/2 hadrons from the decay of short-lived ($\ensuremath{\tau}<{10}^{\ensuremath{-}21}\mathrm{sec}$) 2He^{2}\mathrm{He}2He spin-singlet state, populated in the nuclear reaction $^{2}\mathrm{H}+^{1}\mathrm{H}\ensuremath{\rightarrow}^{2}\mathrm{He}+n$. The novel features of this experiment are (a) the use of an ``event-ready'' detector of nearly 100% efficiency to prepare an unbiased sample and (b) a focal-plane polarimeter of full $2\ensuremath{\pi}\text{ }\text{ }\mathrm{sr}$ acceptance with a random ``post selection'' of the reference axes. The spin-correlation function is deduced to be ${S}_{\mathrm{exp}}(\ensuremath{\pi}/4)=2.83\ifmmode\pm\else\textpm\fi{}{0.24}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}{0.07}_{\mathrm{sys}}$. This result is in agreement with nonlocal quantum mechanical prediction and it violates the Bell-CHSH inequality of $|S|\ensuremath{\le}2$ at a confidence level of 99.3%.
The project concerned the study of quantum correlations (QC) in compound systems, i.e. statistical correlations more general than entanglement which are predicted by quantum mechanics but not described in any classical scenario. I aimed to understand the technical and operational properties of the measures of QC, their interplay with entanglement quantifiers and the experimental accessibility.\nIn the first part of my research path, after having acquired the conceptual and technical rudiments of the project, I provided solutions for some computational issues: I developed analytical and numerical algorithms for calculating bipartite QC in finite dimensional systems. Then, I tackled the problem of the experimental detection of QC. There is no Hermitian operator associated with entanglement measures, nor with QC ones. However, the information encoded in a density matrix is redundant to quantify them, thus the full knowledge of the state is not required to accomplish the task. I reported the first protocol to measure the QC of an unknown state by means of a limited number of measurements, without performing the tomography of the state. My proposal has been implemented experimentally in a NMR (Nuclear Magnetic Resonance) setting.\nIn the final stage of the project, I explored the foundational and operational merits of QC. I showed that the QC shared by two subsystems yield a genuinely quantum kind of uncertainty on single local observables. The result is a promising evidence of the potential exploitability of separable (unentangled) states for quantum metrology in noisy conditions.
We discuss the peculiarities of scattering in a three-proton system induced by the presence of an entangled proton-proton Bell-like state in the initial configuration. We formulate the problem using the standard spin formalism of nuclear physics in order to follow in detail the reaction pathways leading to the teleportation of a quantum-mechanical state within this system. By performing numerical simulations of the system and calculations based on a realistic nucleon-nucleon potential, we evaluate the relevant spin observables and search for a simple, experimentally feasible signal that could provide clear evidence of quantum teleportation. For the case in which proton 2, belonging to the entangled proton pair 23, interacts with hydrogen target 1, thereby triggering the teleportation process, we find clear evidence of teleportation through measurements of the final polarization of proton 3', even for small values of the polarization of target proton 1. The dominant component of this polarization is transferred almost entirely from target proton 1 to proton 3 in the angular region characterized by strong entanglement. For an unpolarized target proton 1, quantum teleportation is no longer possible. The only unambiguous signature of the residual quantum correlations would be provided by measurements of the spin correlations within the strongly entangled final-state proton pair 1'2'. Indirect evidence may also be obtained from measurements of the polarization of proton 2' in the final state, although the corresponding effectis relatively weak.