Browsing by Subject "Information theory."

Now showing 1 - 3 of 3

Open Access
Entanglement : quantification via uncertainties and search among ultracold bosons in optical lattices
(2009) Öztop, Barış
In the first part of the Thesis, the known measures of entanglement for finite dimensional systems are reviewed. Both the simplest case of pure states that belong to bipartite systems and more general case of mixed states are discussed. The multipartite extensions are also mentioned. In addition to the already existing ones, we propose a new measure of entanglement for pure states of bipartite systems. It is based on the dynamical symmetry group approach to quantum systems. The new measure is given in terms of the total uncertainty of basic observables for the corresponding state. Unlike conventional measures concurrence and 3-tangle, which measure the amount of entanglement of different groups of correlated parties, our measure gives the total amount of multipartite entanglement in a specific state. In the second part of the Thesis, the trapping of bosonic atoms in optical lattices is reviewed. The band structure together with Bloch functions and Wannier basis are discussed for this system. In relation with that, the corresponding Bose-Hubbard model and by the use of this model, the resulting superfluid to Mott-insulator quantum phase transition is summarized. In this regard, the Bose-Hubbard Hamiltonian of a specific system, namely ultracold spin-1 atoms with coupled ground states in an optical lattice is considered. For this system we examine particle entanglement, that is characterized by pseudo-spin squeezing both for the superfluid and Mott-insulator phases in the case of ferromagnetic and antiferromagnetic interactions. The role of a small but nonzero angle between the polarization vectors of counterpropagating lasers forming the optical lattice on quantum correlations is investigated as well.
Open Access
Entanglement in local systems
(2008) Binicioğlu Çetiner, Sinem
In this study, we first discuss entanglement measures and we introduce a way to construct generic entangled states of an n-level quantum system. Then we discuss entanglement as a local object. Particularly we use a spin qutrit, and investigate whether an entangled spin qutrit obeys entanglement criteria or not. While doing this, we also discuss, which criteria of entanglement are essential and which of them are not. We show the relation between quantum fluctuations and entanglement. Lastly, we discuss Bell type inequalities and we show violation of a Bell type condition by a single particle entangled state.
Open Access
Joint source channel coding using sequential decoding
(1997) Doğrusöz, Bekir Ahmet
In systems using conventional source encoding, source sequence is changed into a series of approximately independent equally likely binary digits. Performance of a code is bounded with the rate distortion function and improves as the redundancy of the encoder output is decreased. However decreasing the redundancy implies increasing the block length and hence the complexity. For the systems requiring low complexity at transmitter, joint source channel (JSC) coding can be successfully used for direct encoding of source into the channel for lossless recovery. In such a system, without any distortion, compression depends on the redundancy of the source, and is bounded by the Renyi entropy of the source. In this thesis we analyze transmission of English text with a JSC coding system. Written English is a good example for sources with natural redundancy. Since we are unable to calculate the Renyi entropy of written English, we obtain estimates and compare with the experimental results. We also work on an alternative source encoding method for accuracycompression trade-off in joint source channel coding systems. The proposed stochastic distortion encoder (SDE) is capable of achieving accuracycompression trade-off at any average distortion constraint with very low block lengths, and hence performs better than or as good as an equivalent rate distortion encoder. As block length approaches infinity the performance of stochastic distortion encoder approaches rate distortion function. Formulations for optimal SDE design and results for block lengths 1,2 and 3 are also given.