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Title: Violation of entropic Leggett-Garg inequality in nuclear spins
Authors: Katiyar, Hemant
Shukla, Abhishek
Rao, K. Rama Koteswara
Dept. of Physics
Keywords: Violation of entropic
Leggett-Garg inequality
Nuclear spins
Noninvasive measurements
Issue Date: May-2013
Publisher: American Physical Society
Citation: Physical Review A, 87(5), 052102.
Abstract: We report an experimental study of recently formulated entropic Leggett-Garg inequality (ELGI) by Usha Devi et al. [Phys. Rev. A 87, 052103 (2013)]. This inequality places a bound on the statistical measurement outcomes of dynamical observables describing a macrorealistic system. Such a bound is not necessarily obeyed by quantum systems, and therefore provides an important way to distinguish quantumness from classical behavior. Here we study ELGI using a two-qubit nuclear magnetic resonance system. To perform the noninvasive measurements required for the ELGI study, we prepare the system qubit in a maximally mixed state as well as use the “ideal negative result measurement” procedure with the help of an ancilla qubit. The experimental results show a clear violation of ELGI by over four standard deviations. These results agree with the predictions of quantum theory. The violation of ELGI is attributed to the fact that certain joint probabilities are not legitimate in the quantum scenario, in the sense they do not reproduce all the marginal probabilities. Using a three-qubit system, we also demonstrate that three-time joint probabilities do not reproduce certain two-time marginal probabilities.
ISSN: 1050-2947
Appears in Collections:JOURNAL ARTICLES

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