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It is well known that environmental decoherence is a crucial barrier in realizing various quantum information processing tasks; on the other hand, it plays a pivotal role in explaining how a quantum system's fragile state leads to a robust classical state. Zurek (Nat Phys 5(3):181–188, 2009) was the first to develop the theory which successfully describes the emergence of classical objectivity of quantum systems using decoherence, introduced by the environment. Here, we consider an n-qubit generalized quantum circuit for the quantum system–environment interaction model, where the first qubit represents the quantum system, and the rest are for the environmental fragments. This quantum circuit is implemented on ibmq_athens and ibmq_16_melbourne for n = 2 , 3 , 4 , 5 , 6 . Its accuracy is checked using quantum state tomography and enhanced using the quantum error mitigation procedure. The reconstructed density matrices are used to investigate quantum-classical correlation and the mutual information between the quantum system and the environment. The investigation proves the quantum Darwinism principle when the quantum circuits are executed on the noise-less simulator; however, it shows the unaccountable behavior when implemented on the real quantum devices. The results via the noise-less simulator successfully prove that the environmental fragment size and the interaction strength play a crucial role in the emergence of classicality. [ABSTRACT FROM AUTHOR]

Quantum secret sharing is a way to share secret messages among the clients in a group with complete security. For the first time, Hillery et al. (Phys Rev A 59:1829, 1999) proposed the quantum version of classical secret sharing protocol using GHZ states. Here, we implement the above quantum secret sharing protocol in 'IBM Q 5 Tenerife' quantum processor and compare the experimentally obtained results with the theoretically predicted ones. Further, a new quantum binary voting protocol is proposed and implemented in the 14-qubit 'IBM Q 14 Melbourne' quantum processor. The results are analyzed through the technique of quantum state tomography, and the fidelity of states is calculated for different number of executions made in the device. [ABSTRACT FROM AUTHOR]