Article
Optics
Hiroo Azuma, William J. Munro, Kae Nemoto
Summary: We investigate the Leggett-Garg inequalities (LGIs) in a boson system by deforming the Pegg-Barnett phase operators. The quantum Fourier transform is used for the required measurements. The explicit forms of the LGIs are derived using the coherent state |alpha) as the initial state, and the violation of LGIs is explored with varying time difference between observations of the phase operators. The nonclassicality of the system remains in the large amplitude limit without dissipation, but diminishes rapidly with dissipation.
Article
Physics, Particles & Fields
Xing-Zhi Wang, Bo-Qiang Ma
Summary: This study presents a Leggett-Garg-type inequality compatible with neutrino oscillation frameworks, and applies it to test coherence in different experiments. The results show clear violations of the inequality in the Daya Bay and MINOS data, while KamLAND data also exhibit some violations.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Optics
H. S. Karthik, H. Akshata Shenoy, A. R. Usha Devi
Summary: The Leggett-Garg inequality explores the macrorealistic limit in the quantum domain, and it has been shown that in N>2 quantum systems, the three-term inequality can be violated beyond the TTB 3/2 through suitable measurement schemes and state-update rules.
Article
Physics, Multidisciplinary
Asmita Kumarr, A. K. Pan
Summary: This paper studies two formulations of LGIs in the three-time LG scenario and analyzes the quantum violation under non-unitary quantum channels. The study finds that the quantum violations of LGIs can be obtained at lower values of the unsharpness parameter when the measurements are unsharp in non-unitary dynamics. Additionally, the paper discusses the relationship between the violation of Luders bound of LGIs and the violation of various no-signaling in time conditions.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2022)
Article
Optics
C. Mawby, J. J. Halliwell
Summary: Macrorealism is a worldview that asserts certain quantities have definite values at all times, which can be experimentally falsified through the Leggett-Garg inequalities. In this study, we tested this worldview for systems described by a continuous variable x, specifically for measurements of a dichotomic variable Q = sign(x) in a quantum harmonic oscillator with Gaussian initial states. Our analysis revealed significant violations of the two-time Leggett-Garg inequalities, as well as violations at three and four times. We also explored the physical implications of these violations by analyzing quantum-mechanical currents, Bohm trajectories, and the Wigner function.
Article
Optics
Giuseppe Vitagliano, Costantino Budroni
Summary: Leggett and Garg formulated macrorealist models to test macroscopic quantum coherence effects, but these tests are subject to loopholes. This review discusses recent progress in characterizing macrorealist and quantum temporal correlations, closing the loopholes associated with Leggett-Garg tests, and introduces definitions of nonclassical temporal correlations and their applications in sequential quantum information processing.
Article
Optics
Francesco Giacosa, Giuseppe Pagliara
Summary: The Leggett-Garg inequalities are applied to classical and quantum unstable systems. For classical systems, where the assumptions of macroscopic realism and noninvasive measurements hold, K-3 equals 1; for quantum systems, K-3 equals 1 only for purely exponential decays, while deviations from the exponential decay law predicted by quantum mechanics lead to values of K-3 not equal to 1.
Article
Optics
Massimo Blasone, Fabrizio Illuminati, Luciano Petruzziello, Luca Smaldone
Summary: In this paper, we investigate the Leggett-Garg inequalities for neutrino oscillations in the quantum field theoretical setting. We derive an exact flavor-mass uncertainty relation and prove that this uncertainty product provides an upper bound to the violation of the inequalities. Furthermore, we show that, on average, the inequalities are violated more frequently and more strongly in quantum field theory than in quantum mechanics.
Article
Physics, Multidisciplinary
Javid Naikoo, Swati Kumari, Subhashish Banerjee, A. K. Pan
Summary: The study reveals an enhancement of quantum coherence in a qubit under a parity-time (PT) symmetric Hamiltonian, especially around exceptional points (EPs) where the Leggett-Garg inequality tests show maximal violation.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2021)
Article
Optics
Wenlei Zhang, Ravi K. Saripalli, Jacob M. Leamer, Ryan T. Glasser, Denys I. Bondar
Summary: In contrast to Bell's inequalities which test spatial correlations, the Leggett-Garg inequalities measure temporal correlations within a single system. We experimentally demonstrated the violation of the Leggett-Garg inequality in a classical optical system using only the polarization degree of freedom of a laser beam, showing maximal violations.
Article
Optics
C. Mawby, J. J. Halliwell
Summary: The Leggett-Garg inequalities were applied to test the macroscopic quantum coherence in various types of macroscopic oscillators. The research results showed that there exist parameter spaces in which the inequalities can be violated or satisfied in the one-dimensional quantum harmonic oscillator and other bound systems. Even with experimental imprecision, the violations still persist. However, the violations diminish in higher-energy eigenstates, indicating classicalization. The Morse potential was also analyzed with similar conclusions.
Article
Optics
Shayan Majidy, Jonathan J. Halliwell, Raymond Laflamme
Summary: This paper examines violations of macroscopic realism (MR) in a wider range of data sets and conditions. By exploring different data sets and LGIs, it is found that standard LGIs cannot completely detect violations of MR. The study also discusses possible experimental implementations in various scenarios in a spin-1 system.
Article
Optics
Anders J. E. Bjerrum, Jonatan B. Brask, Jonas S. Neergaard-Nielsen, Ulrik L. Andersen
Summary: In this paper, an all-optical setup is analyzed, which achieves Bell-inequality violation over long distances by using probabilistic entanglement swapping. The setup consists of two-mode squeezers, displacements, beamsplitters, and on-off detectors. The arrangement of events to close both the detection and locality loopholes is described. A scenario with dichotomic inputs and outputs is analyzed, and the robustness of Bell inequality violation is checked for up to six parties, considering phase, amplitude, dark count noise, and loss.
Article
Optics
Tianxiang Zhan, Chunwang Wu, Manchao Zhang, Qingqing Qin, Xueying Yang, Han Hu, Wenbo Su, Jie Zhang, Ting Chen, Yi Xie, Wei Wu, Pingxing Chen
Summary: The Leggett-Garg inequality (LGI) is a method to detect the existence of macroscopic superposition state, where classical systems adhere to LGI while quantum systems may violate it. This study experimentally tests LGI in a three-level trapped-ion system using Luders and von Neumann state update rules. The results show a significant violation of the Luders bound, with K3 = 1.739 +/- 0.014 under the von Neumann state update rule, surpassing the standard deviation by 17 times and being the most significant violation under the specific model. The experimental method employed here can also be applied in other multilevel experiments in trapped-ion systems.
Article
Optics
Anant V. Varma, Jacob E. Muldoon, Sourav Paul, Yogesh N. Joglekar, Sourin Das
Summary: We study the violation of the Leggett-Garg inequality in a two-level system undergoing coherent dynamics described by a non-Hermitian Hamiltonian. By using postselection, we reproduce the violation of the inequality and connect it to the nonuniform speed of evolution on the Bloch sphere. Furthermore, we consider the effects of competing Lindblad dissipators on the postselected non-Hermitian dynamics and discuss the possibility of observing the violation in current experimental setups.
Article
Physics, Multidisciplinary
Keito Hibino, Kazuya Fujiwara, Jun-Yi Wu, Masataka Iinuma, Holger F. Hofmann
EUROPEAN PHYSICAL JOURNAL PLUS
(2018)
Article
Physics, Multidisciplinary
Holger F. Hofmann
FOUNDATIONS OF PHYSICS
(2020)
Article
Physics, Multidisciplinary
Holger F. F. Hofmann, Tomonori Matsushita, Shunichi Kuroki, Masataka Iinuma
Summary: Contrary to common assumption, experimental evidence shows that small polarization rotations applied in the slits of a double-slit experiment physically delocalize individual particles, indicating that their path can be observed.
QUANTUM STUDIES-MATHEMATICS AND FOUNDATIONS
(2023)
Article
Optics
Baihong Li, Holger F. Hofmann
Summary: Broadband energy-time entanglement enhances two-photon absorption rate by precise resonance and short coincidence time. Broadband TPA is not sensitive to intermediate level spectrum, making it optimal for entirely virtual intermediate transitions. By introducing phase dispersion matching intermediate resonances, TPA can be enhanced.
Article
Optics
Ming Ji, Holger F. Hofmann
Summary: This paper investigates the differences between the relations of measurement outcomes represented by nonorthogonal quantum states and the relations suggested by a joint assignment of measurement outcomes that do not depend on the actual measurement context. It demonstrates that the Hilbert space formalism modifies the relation between the measurement outcomes and requires the violation of noncontextual consistency as a consequence of the Hilbert space inner products that describe the contextual relation between the outcomes of different measurements.
Article
Physics, Multidisciplinary
Jonte R. Hance, Ming Ji, Holger F. Hofmann
Summary: By analyzing the quantum Cheshire cat using contextuality theory, we found that the coherence between different states plays a crucial role in its behavior.
NEW JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
Hartmut Lemmel, Niels Geerits, Armin Danner, Holger F. Hofmann, Stephan Sponar
Summary: Recent experimental studies have shown that it is possible to obtain accurate information about the path taken by a particle in a quantum interference scenario by using specific experimental methods, thus overcoming the limitations imposed by conventional uncertainties.
PHYSICAL REVIEW RESEARCH
(2022)
Article
Optics
Baihong Li, Holger F. Hofmann
Summary: This study explores the impact of energy-time entanglement on two-photon absorption (TPA) processes, demonstrating that separating two-photon resonance from the temporal dynamics of intermediate levels simplifies the theory. The introduction of a one-dimensional coherence in the Hilbert space provides a description of the role of entanglement in the TPA process. Additionally, transformation into the frequency-difference basis leads to Kramers-Kronig relations for the TPA process, separating off-resonant contributions from resonant contributions.
Article
Optics
Tomonori Matsushita, Holger F. Hofmann
Summary: Obtaining information about observable properties of a quantum system requires physical interaction with an external meter, which depends on the initial quantum coherence of the meter. The sensitivity of the meter is defined by the distinguishability of meter states for different observable values, and it requires quantum coherences. The tradeoff between measurement resolution and backaction is determined by the relation between sensitivity and quantum coherent uncertainty in the external meter.
Article
Physics, Multidisciplinary
Holger F. Hofmann
Summary: The study demonstrates that measurement uncertainties can be observed directly by evaluating the feedback compensation of decoherence induced by the measured system on a probe qubit. The empirical validity of measurement theories that combine initial information of the input state with additional information provided by each measurement outcome is confirmed by introducing measurement uncertainties described by Ozawa in Phys. Rev. A 67, 042105 (2003).
PHYSICAL REVIEW RESEARCH
(2021)
Article
Optics
Holger F. Hofmann
Article
Optics
Holger F. Hofmann
Article
Physics, Multidisciplinary
Taiki Nii, Masataka Iinuma, Holger F. Hofmann
QUANTUM STUDIES-MATHEMATICS AND FOUNDATIONS
(2018)
Article
Optics
Masataka Iinuma, Masayuki Nakano, Holger F. Hofmann, Yutaro Suzuki
