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Entanglement robostness in continous variable systems and fotodetection of intense light beams in spectral domain

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Author(s):
Felippe Alexandre Silva Barbosa
Total Authors: 1
Document type: Doctoral Thesis
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Instituto de Física
Defense date:
Examining board members:
Marcelo Martinelli; Amir Ordacgi Caldeira; Carlos Henrique Monken; Antonio Fernando Ribeiro de Toledo Piza; Paulo Teotonio Sobrinho
Advisor: Marcelo Martinelli
Abstract

We investigate the entanglement generated by an optical parametric oscillator (OPO) operating above threshold. We showed that the tripartite system, prepared directly from the OPO and composed by the twin beams and the reflected pump field, is completely inseparable. This was the first observation of entanglement between three di_erent frequencies of light. We also investigated the dynamics of entanglement under transmission losses. Depending on the injected pump power, we were able to prepare states with tripartite entanglement between the initial pump and twin beams that was maintained or lost after transmission losses. We extended the study to the bipartite system formed by the twin beams. In this simpler system, we investigated in more detail the robustness of entanglement and the conditions under which the entanglement becomes fragile. We also conducted a heoretical study and derived a suficient condition for the entangled state formed by two modes to be robust against losses. This condition also become necessary for Gaussian states. We also studied the measurement process of intensity fluctuations in the frequency domain. The fluctuations are converted to the radiofrequency range, with bandwidth limited by the detector. This is also reflected in the fact that each frequency component, , of the photocurrent contains the information relative to the two modes of the electromagnetic field equally spaced from its center frequency, the sidebands. Therefore each light beam we describe is actually composed by two modes, making our system more rich. We were able to demonstrate that this hexapartite system generated by our OPO, and composed by the two sidebands of each field, is completely inseparable. We also described under which conditions the approximation of one mode per field, used in our prior work and for almost the entire community, is valid. We also showed that resonator detection is able to completely characterize the system composed by the two sidebands of each field if the state is Gaussian and that homodyne detection, the method used to characterize the quantum state for continuous variables, fails to measure all correlations present in this bimodal system. (AU)

FAPESP's process: 08/58431-9 - Interfacing quantum information between atoms and light
Grantee:Felippe Alexandre Silva Barbosa
Support type: Scholarships in Brazil - Doctorate