Enhanced non-macrorealism: Extreme violations of Leggett-Garg inequalities for a system evolving under superposition of unitaries
Abstract: Quantum theory contravenes classical macrorealism by allowing a system to be in a superposition of two or more physically distinct states, producing physical consequences radically different from that of classical physics. We show that a system, upon subjecting to transform under superposition of unitary operators, exhibits enhanced non-macrorealistic feature - as quantified by violation of the Leggett-Garg inequality (LGI) beyond the temporal Tsirelson bound. Moreover, this superposition of unitaries also provides robustness against decoherence by allowing the system to violate LGI and thereby retain its non-macrorealistic behavior for a strikingly longer duration. Using an NMR register, we experimentally demonstrate the superposition of unitaries with the help of an ancillary qubit and verify these theoretical predictions.
- A. Einstein, B. Podolsky, and N. Rosen, Can quantum-mechanical description of physical reality be considered complete?, Phys. Rev. 47, 777 (1935).
- J. S. Bell, On the einstein podolsky rosen paradox, Physics Physique Fizika 1, 195 (1964).
- R. P. Feynman and F. L. Vernon Jr, The theory of a general quantum system interacting with a linear dissipative system, Annals of physics 281, 547 (2000).
- A. Aspect, J. Dalibard, and G. Roger, Experimental test of bell’s inequalities using time-varying analyzers, Phys. Rev. Lett. 49, 1804 (1982).
- K. Hornberger, Introduction to decoherence theory, in Entanglement and Decoherence: Foundations and Modern Trends (Springer, 2009) pp. 221–276.
- A. J. Leggett and A. Garg, Quantum mechanics versus macroscopic realism: Is the flux there when nobody looks?, Phys. Rev. Lett. 54, 857 (1985).
- A. J. Leggett, Realism and the physical world, Reports on Progress in Physics 71, 022001 (2008).
- A. J. Leggett, Realism and the physical world, in Quantum Theory: A Two-Time Success Story, edited by D. C. Struppa and J. M. Tollaksen (Springer Milan, Milano, 2014) pp. 9–20.
- V. Athalye, S. S. Roy, and T. S. Mahesh, Investigation of the leggett-garg inequality for precessing nuclear spins, Phys. Rev. Lett. 107, 130402 (2011).
- T. Fritz, Quantum correlations in the temporal clauser–horne–shimony–holt (chsh) scenario, New Journal of Physics 12, 083055 (2010).
- C. Budroni and C. Emary, Temporal quantum correlations and leggett-garg inequalities in multilevel systems, Phys. Rev. Lett. 113, 050401 (2014).
- H. S. Karthik, H. Akshata Shenoy, and A. R. U. Devi, Leggett-garg inequalities and temporal correlations for a qubit under pt-symmetric dynamics, Phys. Rev. A 103, 032420 (2021).
- J. Cavanagh, Protein NMR spectroscopy: principles and practice (Academic press, 1996).
- M. H. Levitt, Spin dynamics: basics of nuclear magnetic resonance (John Wiley & Sons, 2008).
- D. G. Cory, A. F. Fahmy, and T. F. Havel, Ensemble quantum computing by nmr spectroscopy, Proceedings of the National Academy of Sciences 94, 1634 (1997).
- N. A. Gershenfeld and I. L. Chuang, Bulk spin-resonance quantum computation, science 275, 350 (1997).
- D. G. Cory, M. D. Price, and T. F. Havel, Nuclear magnetic resonance spectroscopy: An experimentally accessible paradigm for quantum computing, Physica D: Nonlinear Phenomena 120, 82 (1998).
- J. D. Roberts, The bloch equations. how to have fun calculating what happens in nmr experiments with a personal computer, Concepts in Magnetic Resonance 3, 27 (1991).
- D. A. Lidar, Lecture notes on the theory of open quantum systems, arXiv preprint arXiv:1902.00967 10.48550/arXiv.1902.00967 (2019).
- H.-P. Breuer and F. Petruccione, The theory of open quantum systems (Oxford University Press, USA, 2002).
Paper Prompts
Sign up for free to create and run prompts on this paper.