Quantum information with squeezed coherent states of the light

Author(s)

Douglas Delgado de Souza

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin
• Defense date: 2015-07-14

Examining board members

Antonio Vidiella Barranco; Celso Jorge Villas Boas; Reginaldo de Jesus Napolitano; José Antonio Roversi; Marcos César de Oliveira

• Advisor: Antonio Vidiella Barranco

Abstract

In the first part of this work we follow the studies of Hirota and collaborators and we define four quasi-Bell states based on squeezed coherent states of light. Two of these states are maximally entangled, while the entanglement of the other two depends only on the overlap between the squeezed coherent states that were combined. From these quasi-Bell states we define new interpolated states for which the entanglement is also governed by an additional interpolation parameter, and we study some of the properties of these states (entanglement and energy efficiency). Finally, we use these states to define some Werner states, which we use to study in a simple way the possible influence of some dissipative environment parameterized by the probability that the Werner state is entangled or mixed. For this analysis we use the concepts of separability and entanglement. In the second part, we study the quantum phase estimation using pure Gaussian states (squeezed coherent states). We begin with the estimation of the phase introduced by a unitary operator whose Hamiltonian also contains a disturbance that is linear in the creation and annihilation operators in addition to the photon number operator responsible for the phase evolution (unitary linear disturbance). We find what are the optimal Gaussian states for this phase estimation and we also analyze the optimality of the homodyne detection. Next, we consider the disturbance parameter to be a random variable submitted to a Gaussian distribution (random linear disturbance) and again we find what are the optimal probe states and analyze the optimality of the homodyne detection. Finally we study the phase estimation with unitary linear disturbance using the interpolated quasi-Bell states defined in the first part of this work and we verify that the use of entanglement leads to a better phase estimation for the same amount of available energy (AU)

• FAPESP's process: 11/00220-5 - Quantum information based on squeezed coherent states
• Grantee: Douglas Delgado de Souza
• Support Opportunities: Scholarships in Brazil - Doctorate