טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentEli Meirom
SubjectEntanglement in Radiative Cascades
DepartmentDepartment of Physics
Supervisors Professor Emeritus Avron Joseph
Full Professor Gershoni David
Full Thesis textFull thesis text - English Version


Abstract

Two photon radiative cascades with multiple decay paths are candidate sources of entangled pairs of photons. Practical implementations of quantum information theory prefer to deal with flying qubits that are based on the photons' states of polarization. Unfortunately, unless the radiative cascade obeys restrictive symmetry conditions, the 2-qubit state associated with the polarization of the photon pair is mixed and has only negligible entanglement. As these symmetry conditions are very hard to achieve, a distillation procedure is needed in order to obtain polarization entangled qubits.

In this thesis we discuss a novel distillation method which proceeds by spectrally filtering the photons. The method was successfully implemented and polarization entangled qubits from the sequential decay cascade of two electron-hole pairs (biexciton) confined in semiconductor quantum dots were obtained.

In our work we describe a theory that allows one to compute the two qubits polarization density matrix for a general decay cascade, with and without distillation . We describe an appropriate entanglement distillation scheme which works also for certain random cascades. The qualitative features of the distilled entanglement are presented in a two dimensional ``phase diagram''. The theory is applied to the quantum tomography of the decay cascade of a biexciton in a semiconductor quantum dot .