Quantum correlation via quantum coherence

Quantum correlation includes quantum entanglement and quantum discord. Both entanglement and discord have a common necessary condition--------quantum coherence or quantum superposition. In this paper, we attempt to give an alternative understanding of how quantum correlation is related to quantum coherence. We divide the coherence of a quantum state into several classes and find the complete coincidence between geometric (symmetric and asymmetric) quantum discords and some particular classes of quantum coherence. We propose a revised measure for total coherence and find that this measure can lead to a symmetric version of geometric quantum correlation which is analytic for two qubits. In particular, this measure can also arrive at a monogamy equality on the distribution of quantum coherence. Finally, we also quantify a remaining type of quantum coherence and find that for two qubits it is directly connected with quantum nonlocality.Comment: 20 pages, 1 figure. To appear Quant. Inf. Pro

Entropic characterization of coherence in quantum evolutions

By using relative entropy of coherence, we characterize the coherence gain induced by some quantum evolutions, including the cohering power of unitary operations and the decohering power of quantum operations. We find that the cohering power of the controlled unitary operation can be reduced to the cohering power of the corresponding unitary operation. We observe that the global coherence generated via incoherent operation applied to the system and an incoherent ancilla do not exceed the amount of coherence contained in the initial system. Our result provides a much tighter lower bound of coherence for the initial quantum state, and give an interesting chain of inequalities for coherence, quantum correlation and entanglement. We also strengthen the relations between quantum correlations and coherence.Comment: 6 pages, new title, new section and references added, updated version minor typos corrected. Comments are welcome

Experimental demonstrations for randomness-based macroscopic Franson-type nonlocal correlation using coherently coupled photons

Franson-type nonlocal quantum correlation based on the particle nature of quantum mechanics has been intensively studied for both fundamental physics and potential applications of quantum key distribution between remotely separated parties over the last several decades. Recently, a coherence theory of deterministic quantum features has been applied for Franson-type nonlocal correlation [arXiv:2102.06463] to understand its quantumness in a purely classical manner, where the resulting features are deterministic and macroscopic. Here, nearly sub-Poisson distributed coherent photon pairs obtained from an attenuated laser are used for the experimental demonstrations of the coherence Franson-type nonlocal correlation. As an essential requirement of quantum mechanics, quantum superposition is macroscopically provided using polarization basis-randomness via a half-wave plate, satisfying fairness compared with the original scheme based on phase bases. The observed coherence quantum feature of the modified Franson correlation successfully demonstrates the proposed wave nature of quantum mechanics, where the unveiled nonlocal correlation is relied on a definite phase relation between the paired coherent photons.Comment: 9 pages, 3 figures, 1 tabl

Coherence and Fluctuations in the Interaction between Moving Atoms and a Quantum Field

Mesoscopic physics deals with three fundamental issues: quantum coherence, fluctuations and correlations. Here we analyze these issues for atom optics, using a simplified model of an assembly of atoms (or detectors, which are particles with some internal degree of freedom) moving in arbitrary trajectories in a quantum field. Employing the influence functional formalism, we study the self-consistent effect of the field on the atoms, and their mutual interactions via coupling to the field. We derive the coupled Langevin equations for the atom assemblage and analyze the relation of dissipative dynamics of the atoms with the correlation and fluctuations of the quantum field. This provides a useful theoretical framework for analysing the coherent properties of atom-field systems.Comment: 12 pages, Late

Indistinguishable photons from independent semiconductor single-photon devices

We demonstrate quantum interference between photons generated by the radiative decay processes of excitons that are bound to isolated fluorine donor impurities in ZnSe/ZnMgSe quantum-well nanostructures. The ability to generate single photons from these devices is confirmed by auto-correlation experiments, and indistinguishability of single photons from two independent devices is confirmed via a Hong-Ou-Mandel dip. These results indicate that donor impurities in appropriately engineered semiconductor structures can portray atom-like homogeneity and coherence properties, potentially enabling scalable technologies for future large-scale optical quantum computers and quantum communication networks

Two-Photon Correlations in pppp Collisions

It is well understood that the studies of correlations between produced particles, the effects of coherence and chaoticity, an estimation of particle emitting source size play an important role in high energy physics [1]. First of all, we mean the investigation of the space-time extension or even squeezing of particle sources via the multiparticle quantum-statistics correlation. We consider the two-photon correlation function that can provide the space-time information about the Higgs-boson source in thermal environment and estimate the Higgs-boson mass for the first time.Comment: 12 page

Deterministic quantum correlation in an interferometric scheme

Over the last several decades, entangled photon pairs generated from \c{hi}^((2)) nonlinear optical materials via spontaneous parametric down conversion processes have been intensively studied for various quantum correlations such as Bell inequality violation and anticorrelation. In a Mach-Zehnder interferometer, the photonic de Broglie wavelength has also been studied for quantum sensing with an enhanced phase resolution overcoming the standard quantum limit. Here, the fundamental principles of quantumness are investigated in an interferometric scheme for controllable quantum correlation not only for bipartite entangled photon pairs in a microscopic regime, but also for macroscopic coherence entanglement generation.Comment: 7 pages, 4 figure

BEC of Two Photons and Higgs Physics

It is well understood that the studies of correlations between produced particles, the effects of coherence and chaoticity, an estimation of particle emitting source size play an important role in high energy physics [1]. We mean the investigation of the space-time extension or even squeezing of particle sources via the multiparticle quantum-statistics correlation. We obtain the two-photon correlation function that can provide the space-time information about the Higgs-boson source in thermal environment and we argue that such an investigation could probe the Higgs-boson mass.Comment: 13 pages, (version 2, slight revisions and clarifications

Lattice correlation of Hubbard excitons in a Mott insulator Sr2IrO4 and reconstruction of their hopping dynamics via time-dependent coherence analysis of the Bragg diffraction

In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon induced Hubbard excitonic quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4. Combining time-resolved optical spectroscopy techniques, we further reconstructed spatiotemporal map of the diffusion of quasiparticles via time-dependent coherence analysis of the x-ray Bragg diffraction peak. Due to the unique electronic configuration of the exciton, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates under highly non-equilibrium conditions. The coherence analysis method we developed may have important implications for characterizing the structure and carrier dynamics in a wider group of oxide heterostructures.Comment: Main text has 17 pages, 4 figures; supplemental information has 5 pages, 3 figures, and 1 tabl

Interrelation between Partial Coherence and Quantum Correlations

Both coherence and entanglement stem from the superposition principle, capture quantumness of a physical system, and play a central role in quantum physics. In a multipartite quantum system, coherence and quantum correlations are closely connected. In particular, it has been established that quantum coherence of a bipartite state is an important resource for its conversion to entanglement [A. Streltsov {\it et al.}, Phys. Rev. Lett. {\bf 115}, 020403 (2015)] and to quantum discord [J. Ma {\it et al}., Phys. Rev. Lett. {\bf 116}, 160407 (2016)]. We show here that there is a very close association between partial coherence introduced by Luo and Sun [S. Luo and Y. Sun, Phys. Rev. A {\bf 96}, 022136 (2017)] and quantum correlations (quantified by quantum discord) in both directions. Furthermore, we propose families of coherence measures in terms of quantum correlations and quantum Fisher information.Comment: 6 pages, 2 figures, close to published versio