Nonclassical Effects and Dynamics of Quantum Observables

Alfredo Luis, Laura Ares

According to Born's rule quantum probabilities are given by the overlap between the system state and measurement states in a quite symmetrical way. This means that both contribute to any observed nonclassical effect that is usually attributed just to the observed light state. This is relevant since typical measurement are highly nonclassical by themselves, such as number states and quadrature eigenstates. We show that nonclassical effects only arise provided that the measurement is itself nonclassical. Otherwise there is a classical-like model accounting for the observed statistics.

Kevin Costello, Owen Gwilliam

E. Rafiepoor, M. R. Bazrafkan, Saeed Batebi

Liang-Hui Du, Xiang-Fa Zhou, Zheng-Wei Zhou +2 more

We consider the effect of the quadratic term ${\stackrel{P\vec}{A}}^{2}$ on quantum state transfer, nonclassical state preparation, and collapse-revival dynamics in the strong and ultrastrong coupling regime. Using the Bogoliubov transformation, we define a field mode which allows us to reduce the Hamiltonian to the original Rabi form without the ${\stackrel{P\vec}{A}}^{2}$ term. We calculate the error introduced by the ${\stackrel{P\vec}{A}}^{2}$ term in quantum state transfer and find it cannot be neglected in the strong coupling regime. We also study how it impacts the characteristics of the prepared nonclassical states and collapse-revival dynamics. The double-peak characteristic of the revival dynamics can be experimentally observed as manifestation of the effect of the ${\stackrel{P\vec}{A}}^{2}$ term.

Subhashish Banerjee

Kishore Thapliyal

Nonclassical states, having no classical analogue, promise advantage in the performance in several fields of technology, such as computation, communication, sensing. This led to an escalated interest in the recent years for the generation and characterization of nonclassical states in various physical systems of interest. Keeping this in mind, we examined generation of various lower- and higher-order nonclassical states in both codirectional and contradirectional asymmetric nonlinear optical couplers operating under second harmonic generation with the help of moments-based criteria. Using another such system (a symmetric nonlinear optical coupler), we have also established the possibility of observing quantum Zeno and anti-Zeno effects and further reduced the obtained results to yield the corresponding expressions for the asymmetric coupler. These studies have been accomplished using a complete quantum description of the system considering all the field modes as weak. Further, characterization of nonclassicality in spin systems using quasiprobability distributions has been performed, which has also provided us the dynamics of the amount of nonclassicality (using nonclassical volume). As the reconstruction of quasiprobability distributions is possible with the help of tomograms accessible in the experiments, tomograms are computed here for both finite and infinite dimensional systems. Finally, a set of controlled quantum communication (both insecure and secure) schemes with minimum number of entangled qubits has been proposed, which is also analyzed over Markovian channels. The optimized controlled secure quantum communication scheme is observed to be reducible to several cryptographic tasks. Using this interesting observation, we obtained the performance of a set of cryptographic schemes over non-Markovian channels, too.