Quantum Nondemolition Measurement Enables Macroscopic Leggett-Garg Tests

Budroni, C. and Vitagliano, G. and Colangelo, G. and Sewell, R. J. and Gühne, O. and Tóth, Géza (2015) Quantum Nondemolition Measurement Enables Macroscopic Leggett-Garg Tests. PHYSICAL REVIEW LETTERS, 115 (20). ISSN 0031-9007

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Abstract

We show how a test of macroscopic realism based on Leggett-Garg inequalities (LGIs) can be performed in a macroscopic system. Using a continuous-variable approach, we consider quantum non-demolition (QND) measurements applied to atomic ensembles undergoing magnetically-driven coherent oscillation. We identify measurement schemes requiring only Gaussian states as inputs and giving a significant LGI violation with realistic experimental parameters and imperfections. The predicted violation is shown to be due to true quantum effects rather than to a classical invasivity of the measurement. Using QND measurements to tighten the “clumsiness loophole” forces the stubborn macrorealist to re-create quantum back action in his or her account of measurement.

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