Article
Quantum Science & Technology
Yuxia Zhang, Xiangguan Tan
Summary: In this paper, the authors investigate the effects of projective and coarsening measurements on the Leggett-Garg inequality (LGI), the Wigner form of Leggett-Garg inequality (WLGI), and the no-signaling-in-time (NSIT) condition. It is found that the NSIT condition can be violated over a wider parameter range compared to the WLGI, and the WLGI can be violated over a wider parameter range than the LGI under projective measurement. Furthermore, the study shows that the robustness of the LGI and the WLGI are equally vulnerable under coarsening measurements, while the NSIT condition is the most robust. Additionally, the robustness of the coarsening measurement in temporal reference is found to be the most robust, while that of the coarsening in final measurement resolution is the most vulnerable.
QUANTUM INFORMATION PROCESSING
(2022)
Article
Physics, Multidisciplinary
A. K. Pan
Summary: Macrorealism is a fundamental belief in perceiving reality in our everyday world. The Leggett-Garg (LG) test is a conceptually elegant method to investigate the compatibility between macrorealism and quantum theory. However, the lack of consensus on fixing the operational invasiveness loophole, specifically the statistical form of non-invasive measurability assumption, hinders achieving conclusive LG tests. This study proposes a simple and elegant scheme based on indefinite causal order in a quantum switch experiment to close this loophole and ultimately enable a conclusive test of macrorealism in the LG test.
Article
Physics, Multidisciplinary
Swati Kumari, A. K. Pan
Summary: The article discusses the Bell's inequality in a two-party, two-input, and two-output measurement scenario, as well as the discussion on the incompatibility between macrorealism and quantum theory.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2021)
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
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
Joanna K. Kalaga, Anna Kowalewska-Kudlaszyk, Mateusz Nowotarski, Wieslaw Leonski
Summary: We investigated the time correlations of a quantum nonlinear Kerr-like oscillator pumped by ultrashort coherent pulses, analyzing the violation of the Leggett-Garg inequality. We observed how these correlations change as the system's dynamics transition between regular and chaotic regions in its classical counterpart.
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
Physics, Multidisciplinary
Sayan Ghosh, Anant V. Varma, Sourin Das
Summary: We study Leggett-Garg inequalities (LGIs) for a two level system (TLS) undergoing Markovian dynamics described by unital maps. We find the analytic expression of LG parameter K-3 (simplest variant of LGIs) in terms of the parameters of two distinct unital maps representing time evolution for intervals: t(1) to t(2) and t(2) to t(3). We show that the maximum violation of LGI for all possible unital maps can never exceed Luders bound of K-3(Luders ) = 3/2. Our findings establish a threshold for decoherence which will allow for K-3 = K-3(Luders ) and demonstrate the importance of temporal sequencing of the exposure of a TLS to Markovian baths in obtaining Luders bound.
JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL
(2023)
Article
Optics
Manushan Thenabadu, M. D. Reid
Summary: This study proposes delayed-choice experiments with macroscopic qubits and investigates the implications of macroscopic retrocausality. The results demonstrate that the retrocausal behavior can be explained and avoided through extra dimensions and additional unitary dynamics. However, Einstein-Podolsky-Rosen type paradoxes pointing to the incompleteness of quantum mechanics still exist at the microscopic level.
Article
Physics, Nuclear
Sheeba Shafaq, Poonam Mehta
Summary: In this study, the quantum nature of three-flavor neutrino oscillations was explored by investigating the violation of Leggett-Garg inequalities when non-standard interactions were taken into consideration. The results showed an enhancement in the violation of LGI compared to the standard scenario, with appropriate choice of NSI parameters.
JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Junghee Ryu, Daemin Lee, Jinhyoung Lee, Pawel Kurzynski, Dagomir Kaszlikowski
Summary: In this study, genuine monogamy relations for a class of Bell type inequalities are proposed using simple geometric properties of probabilistic spaces and the no-signaling principle, extending the method to qubits and d-dimensional tripartite systems and demonstrating their monogamous nature.
NEW JOURNAL OF PHYSICS
(2021)
Article
Optics
Su Hyun Kim, Han Seb Moon
Summary: The experiment simulated the violation of the Leggett-Garg inequality using a heralded single-photon source generated by SPDC in a PPKTP crystal. The polarization fringe of the photons was measured and analyzed according to n measurements, with simulation results based on the polarization of the heralded single photon in good agreement with theoretical calculations.
KOREAN JOURNAL OF OPTICS AND PHOTONICS
(2021)
Article
Physics, Particles & Fields
Massimo Blasone, Fabrizio Illuminati, Luciano Petruzziello, Kyrylo Simonov, Luca Smaldone
Summary: We investigate two necessary and sufficient conditions for macrorealism, namely no-signaling-in-time and arrow-of-time conditions, in the context of neutrino flavor transitions using both the plane wave description and the wave packet approach. We then compare our findings with the implications of various formulations of Leggett-Garg inequalities. Our results show that the fulfillment of the addressed conditions for macrorealism in neutrino oscillations implies the fulfillment of the Leggett-Garg inequalities, but not vice versa. Additionally, within the framework of the wave packet approach, we demonstrate that the no-signaling-in-time condition is always violated for distances longer than the coherence length, while the Leggett-Garg inequalities are not.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Engineering, Multidisciplinary
Gauresh Raj Jassal, Bryan E. Schmidt
Summary: High fidelity near-wall velocity measurements in wall bounded fluid flows pose a challenge. This study successfully improves the accuracy of measurements by implementing a no-slip boundary condition in a wavelet-based optical flow velocimetry method, contributing to our understanding of near-wall velocity behavior in turbulent boundary layers.
MEASUREMENT SCIENCE AND TECHNOLOGY
(2023)
Article
Quantum Science & Technology
Debashis Saha, Rafael Santos, Remigiusz Augusiak
Article
Quantum Science & Technology
Anubhav Chaturvedi, Debashis Saha
Article
Physics, Multidisciplinary
Chandan Datta, Tanmoy Biswas, Debashis Saha, Remigiusz Augusiak
Summary: This research investigates the distinguishability of quantum measurements using two strategies, finding that quantum entanglement can provide an advantage in measurement discrimination. It is shown that any advantage in measurement discrimination tasks over single systems is a demonstration of Einstein-Podolsky-Rosen 'quantum steering'. Additionally, it is proven that all pure two-qubit entangled states provide an advantage in a measurement discrimination task over one-qubit systems.
NEW JOURNAL OF PHYSICS
(2021)
Article
Quantum Science & Technology
Shubhayan Sarkar, Debashis Saha, Jedrzej Kaniewski, Remigiusz Augusiak
Summary: Bell nonlocality as a resource for device-independent certification schemes has been extensively studied, and a self-testing protocol for the maximally entangled state of any local dimension using the minimum number of measurements possible has been proposed, which can achieve unbounded randomness expansion and log 2d perfect random bits with only one random bit required for encoding measurement choice.
NPJ QUANTUM INFORMATION
(2021)
Article
Physics, Multidisciplinary
Rafael Santos, Debashis Saha, Flavio Baccari, Remigiusz Augusiak
Summary: Bell nonlocality, a remarkable feature of quantum mechanics, is increasingly applied in device-independent protocols. Violations of Bell inequalities can reveal various quantum properties, including entanglement detection and quantification. However, characterizing nonlocal correlations for many-body systems is computationally challenging, and there is no known general method to tailor Bell inequalities for a given state. In this work, we present a general construction of Bell expressions specifically designed for graph states of any prime local dimension, which have broad applications in quantum information.
NEW JOURNAL OF PHYSICS
(2023)
Article
Physics, Multidisciplinary
Shashank Gupta, Debashis Saha, Zhen-Peng Xu, Adan Cabello, A. S. Majumdar
Summary: Despite the importance of contextuality in quantum mechanics, applications requiring contextuality but not entanglement are limited. We demonstrate that any quantum state and observables producing contextuality of sufficiently small dimensions can be used for a communication task with quantum advantage. Conversely, any quantum advantage in this task can prove contextuality under an additional condition. We further show that a set of observables allowing for quantum state-independent contextuality can be used in communication tasks where the difference between classical and quantum communication complexities increases with the number of inputs. Finally, we explain how these communication tasks can be converted into semi-device-independent protocols for quantum key distribution.
PHYSICAL REVIEW LETTERS
(2023)
Article
Physics, Applied
Shubhayan Sarkar, Jakub J. Borkala, Chellasamy Jebarathinam, Owidiusz Makuta, Debashis Saha, Remigiusz Augusiak
Summary: Certification of quantum systems and their properties has become a field of intensive study. In this research, a self-testing scheme is proposed for certifying all bipartite entangled states using minimal measurements. The scheme also allows for certification of rank-one extremal measurements, including nonprojective outcomes, which can be used for certifying the maximum amount of randomness. Furthermore, an extended Bell scenario is proposed for transforming the self-testing scheme to an almost device independent one, specifically in the case of d = 3.
PHYSICAL REVIEW APPLIED
(2023)
Article
Optics
Debashis Saha, Debarshi Das, Arun Kumar Das, Bihalan Bhattacharya, A. S. Majumdar
Summary: This article investigates the phenomenon of measurement incompatibility in quantum communication, demonstrating that the input-output probabilities for classical systems with shared randomness are equivalent to those for d-dimensional quantum strategies with shared randomness and compatible measurements in any communication scenario. Therefore, measurement incompatibility is necessary for quantum advantage in communication, and any quantum advantage serves as evidence of measurement incompatibility at the receiver's end in a semi-device-independent manner. The article introduces a class of communication tasks, a general version of random access codes, to witness the incompatibility of arbitrary numbers of quantum measurements with arbitrary outcomes on d-dimensional systems, providing generic upper bounds on the success metric for compatible measurements. The sets of three incompatible rank-one projective qubit measurements that can be witnessed by random access codes are identified. Finally, the article presents the generic relationship between different sets of probability distributions-classical, quantum with or without shared randomness, and quantum restricted to compatible measurements with or without shared randomness-produced in communication scenarios.
Article
Optics
Shubhayan Sarkar, Debashis Saha
Summary: By exploiting the tension between the two dynamics of quantum theory in the Wigner's Friend thought experiment, this study highlights the inconsistency in observed probabilities of measurement outcomes between two superobservers. To address this issue, two distinct perspectives are hypothesized: absoluteness of measurement (AoM) and nonabsoluteness of measurement (NoM). An operational approach is introduced to test the validity of these two perceptions in quantum theory without assuming experimental details. The findings reveal that the set of probabilities obtainable for NoM is strictly larger than that obtainable for AoM, and a strict hierarchy among the sets of probabilities observed in classical/local realist theory, quantum theory with AoM, and quantum theory with NoM is presented in scenarios with spatially separated observers.
Article
Optics
Sumit Nandi, Debashis Saha, Dipankar Home, A. S. Majumdar
Summary: In this paper, a further generalization of Wigner's approach is presented by deriving a set of LR inequalities for all different bipartitions of a multipartite system. The violations of these inequalities rigorously certify the multipartite nonlocality and identify the corresponding bipartitions exhibiting nonlocality.
Article
Optics
Shubhayan Sarkar, Debashis Saha, Remigiusz Augusiak
Summary: In this letter, we discuss the certification problem of quantum measurements and propose a simple scheme for certifying incompatible projective measurements and the maximally entangled state. We also study the robustness of self-testing results for genuinely incompatible measurements.
Article
Quantum Science & Technology
Debarshi Das, Ananda G. Maity, Debashis Saha, A. S. Majumdar
Summary: Certification of quantum devices is crucial before utilizing them for information processing tasks. This paper presents a certification protocol for a particular set of d-outcome quantum measurements, using a setup comprising of preparation and two sequential measurements. The protocol involves a set of temporal inequalities involving correlation functions and quantum violations of these inequalities are used to certify specific d-outcome measurements efficiently in an experiment. The protocol is robust against practical non-ideal realizations and does not require prior knowledge about the system dimension. Additionally, a scheme for secure certification of quantum randomness is presented as an offshoot of the protocol.
Article
Quantum Science & Technology
Kaushik Joarder, Debashis Saha, Dipankar Home, Urbasi Sinha
Summary: In this experiment, conducted using a sophisticated single-photon experimental setup, we comprehensively addressed the crucial loopholes in macrorealism experiments and successfully demonstrated clear violations of the Leggett-Garg inequality (LGI) and Wigner's form of the Leggett-Garg inequality (WLGI). The experimental results are consistent with quantum mechanical predictions and confirm the noninvasiveness of our implemented negative result measurement.
Article
Physics, Multidisciplinary
R. Salazar, M. Kamon, K. Horodecki, D. Goyeneche, D. Saha, R. Ramanathan, P. Horodecki
Summary: A fundamental question in device-independent quantum cryptography is the determination of the minimal physical principle for the security of cryptographic protocols. The principle of relativistic causality has been considered a candidate for certification of device-independent security, but recent studies show that it is not sufficient. While the no-signaling constraints are necessary but not sufficient for relativistic causality, a refined set of constraints has been proposed to capture the notion more precisely.
PHYSICAL REVIEW RESEARCH
(2021)
Article
Optics
Alley Hameedi, Breno Marques, Piotr Mironowicz, Debashis Saha, Marcin Pawlowski, Mohamed Bourennane
