The origin of squeezing in a superposition of coherent states

Hari Prakash, Pankaj Kumar

Ho Sy Chuong, Truong Minh Duc

Abstract In this paper, we study some non-classical properties of the superposition of photon-added pair coherent state (SPAPCS) such as two-mode sum squeezing and entanglement. The obtained results show that this state has two-mode sum squeezing behavior but the pair coherent state does not. The degree of squeezing of the SPAPCS is enhanced as more and more photons are added to the two modes of the original pair coherent state. Besides, this state is an entangled state and the entanglement degree can be enhanced by adding photons to both modes of the state. When using the SPAPCS as an entangled resource for a coherent state quantum teleportation, it is shown that the quantum teleportation process is successful and the average fidelity of the process can be higher than that of the case where the original pair coherent state is used if the parameters are selected appropriately.

Vladimír Bužek, P. L. Knight, A. Vidiella-Barranco

We investigate the nature of the quantum fluctuations in a light field created by the superposition of coherent fields. We give a physical explanation (in terms of Wigner functions and phase-space interference) why the 1-D superposition of coherent states in the direction of the x-quadrature leads to the squeezing of fluctuations in the y-direction, and show that such a superposition can generate the squeezed vacuum and squeezed coherent states.

Hari Prakash, Pankaj Kumar

Hari Prakash, Pankaj Kumar

Samuel L. Braunstein

We study the first-order perturbation contribution of a generic Markovian master equation on a general superposed quantum state. From this we obtain a universal formula describing the decay of quantum superpositions for arbitrary quantum superpositions. For single-photon damping, superposed coherent states appear, naively, to give the smallest damping rate. However, a comparison of damping rates, based on the observability of superposition fringes, shows that superposed squeezed states can do significantly better than their coherent state rivals. The optimum squeezed superposition is shown to have a damping rate (for the zero-temperature Markovian master equation) linear in the phase-space distance between the pieces of the original unsqueezed superposition, as compared with the quadratic dependence for superpositions of coherent states. Finally, we show that superpositions of squeezed states can be generated directly from squeezed states without having to squeeze a superposition.