Halide double perovskites have recently received considerable attention owing to their promising properties for a range of technological demands. Compounds Cs2MZ6 (M = Ti, Zr, Hf; Z = Cl, I) have been studied individually through experimental synthesis and computational modeling. Nevertheless, comprehensive comparative analyses of their optical characteristics, quantum efficiency, and photocatalytic potential for water splitting remain limited. In this study, the structural, electronic, optical, quantum efficiency, and photocatalytic properties for water splitting of Cs2MZ6 (M = Ti, Zr, Hf; Z = Cl, I) phases are systematically investigated via the full-potential linearized augmented plane wave plus local orbitals technique. The calculated band structures indicate a gradual decrease in the bandgap from Cl to I substitution, with most variants exhibiting indirect and relatively wide gaps. “The frequency-dependent optical properties, including the real and imaginary parts of the dielectric function, absorption coefficient, and optical conductivity, are systematically calculated up to 12 eV. The results reveal pronounced absorption peaks in the ultraviolet region, highlighting the potential of these compounds for high-frequency optoelectronic applications.” Thermodynamic stability was assessed via calculations of Gibbs free energy (kJ/mol) and entropy (S, J mol−1 K−1) as functions of temperature and pressure. The results consistently exhibit negative Gibbs free energies and rising entropy, indicating robust thermal stability. Furthermore, the computed band edge positions indicate potential for photocatalytic water splitting, with Cs2ZrI6 and Cs2HfI6 showing particularly favorable alignment for both hydrogen and oxygen evolution reactions under solar irradiation.

The entropic uncertainty relation imposes a limit on the accuracy of measurement outcomes of two conjugate observables, which can be reduced in the presence of quantum memory. We theoretically study the dynamical behaviors of the quantum-memory-assisted entropic uncertainty relation for a bipartite system under local nonequilibrium dephasing environments and a common nonequilibrium dephasing environment. Particularly, we study the influence of the competition between nonequilibrium and non-Markovianity in controlling the entropic uncertainty bound (EUB) in weak- and strong-coupling regimes. We find that the nonequilibrium nature renders a promising protocol to efficiently harness the EUB in both regimes without requiring any operations on the main system. Further, we reveal that the EUB can be significantly reduced in a common bath case compared to the case of local baths. Moreover, we elucidate the primary factor responsible for governing the dynamical behaviors of EUB by examining the interplay between quantum discord and the minimal missing information about the particle to be measured. In addition, we investigate the state preparation and measurement choice (SPMC) condition in both environmental setups with weak- and strong-coupling regimes. Remarkably, we show that the SPMC condition does not hold in the common environment scenario.

We theoretically investigate an efficient scheme for quantum state transfer (QST) between two nitrogen-vacancy (N-V) centers coupled to the whispering gallery modes (WGM) of a micro-resonator. We analyze the impact of mode coupling and the distance between two N-V centers on the dynamics of state transfer. Specifically, we explore QST under three coupling regimes:comparable coupling (J ≃ g), strong mode coupling J ≫ g, and weak mode coupling J ≪ g, also incorporating system decay factors (WGM decay Γ and N-V dephasing γ) at different interparticle distances. Our study shows that by adjusting the system control parameters, quantum information can be transferred between N-V centers with high efficiency. Additionally, the fidelity of QST reaches approximately 99% in all cases, with an oscillatory pattern, reflecting the intricate interplay between NV-resonator and mode coupling strengths. These findings underscore the importance of interparticle distance and mode coupling in the realization of solid-state qubit-based quantum information processing devices.

Spin-mechanical hybrid systems have been widely used in quantum information processing. However, the spin-mechanical interaction is generally weak, making it a critical challenge to enhance the spin-mechanical interaction into the strong coupling or even ultra-strong coupling regime. Here, we propose a protocol that can significantly enhance the spin-mechanical coupling strength with a diamond spin vacancy and a levitated micromagnet. A driving electrical current is used to modulate the mechanical motion of the levitated micromagnet, which induces a two-phonon drive and can exponentially enhance the spin-phonon and phonon-medicated spin-spin coupling strengths. Furthermore, a high fidelity Schrodinger cat state and an unconventional 2-qubit geometric phase gate with high fidelity and faster gate speed can be achieved using this hybrid system. This protocol provides a promising platform for quantum information processing with NV spins coupled to levitated micromagnets.

The uncertainty principle sets a fundamental bound on the precision of measurement outcomes of two incompatible observables, which can be reduced in the presence of quantum memory. In this work, we investigate the dynamics of entropic uncertainty bound (EUB) for a bipartite system, where only the quantum memory is exposed to a nonequilibrium dephasing environment with an Ohmic-class spectrum, which is compared with the thermal equilibrium case. The nonequilibrium feature is defined by a nonstationary random function which can be controlled by engineering the relative initial phases of the bath modes. We show that this model renders a promising avenue for significantly suppressing the maximum steady-state value of the EUB for all the Ohmic spectral densities. Furthermore, we unveil the role of the reservoir’s Ohmic spectrum and the interplay between quantum discord and minimal conditional entropy of the measured particle in reducing the EUB. Additionally, we examine the state preparation and measurement choice condition in the engineered nonequilibrium environment case. The condition persists, and the nonequilibrium feature serves as a promising tool to impose a stronger limit on entropic uncertainty, enabling more accurate measurement outcomes under decoherence.