Quantum polarization is an important property that has been extensively used for quantum communication purposes. In this work, the mixture of an unpolarized two-mode state and a two-mode pure state is analysed. This mixture is controlled by a single parameter, namely the degree of purity. The quantum polarization of the two-mode mixed state is discussed using the quantum Stokes parameters and the quantum degree of polarization. A relation between the degree of purity and the quantum degree of polarization is established. The mixture is used to model coherent light amplified by an erbium-doped fibre amplifier, which focuses the loss of polarization due to the unpolarized light resulting from spontaneous emission. Finally, the use of such a mixed state in the quantum key distribution using multiphoton pulses is analysed.
Quantum polarization is an important property that has been extensively used for quantum communication purposes. In this work, the mixture of an unpolarized two-mode state and a two-mode pure state is analysed. This mixture is controlled by a single parameter, namely the degree of purity. The quantum polarization of the two-mode mixed state is discussed using the quantum Stokes parameters and the quantum degree of polarization. A relation between the degree of purity and the quantum degree of polarization is established. The mixture is used to model coherent light amplified by an erbium-doped fibre amplifier, which focuses the loss of polarization due to the unpolarized light resulting from spontaneous emission. Finally, the use of such a mixed state in the quantum key distribution using multiphoton pulses is analysed.
Quantum polarisation is an important property that has extensively being used for quantum communication purposes.In this work, initially, the mixture of an unpolarised two-mode state and a two-mode pure state is analysed.Such mixture is controlled by a single parameter, the degree of purity.The quantum polarisation of the twomode mixed state is discussed using quantum Stokes parameters.After, a quantum key distribution set-up using geometric rotating of the quantum polarisation of coherent light pulses is proposed and analysed using both pure and mixed states.
In this dissertation, it is realized a study of light polarization and its applications in quantum communications. Initially, the mathematical tools needed for single-photon and coherent states polarization analyses are presented: coherence matrix, Stokes parameters and polarization degree. Following, using numerical simulations, it is presented the variation of the degree of polarization of a single-photon pulse during depolarizing channel propagation. At last, the result of an experiment using coherent states, aiming to measure the degree of polarization after propagation in 200 m optical fiber is presented. The experiment is useful for determination of the parameter of the qubit depolarizing channel model. Since light polarization is easily changed when environment fluctuations are present during fiber propagation, optical schemes able to correct unpredictable polarization changes are studied. Such schemes are employed for error correction in quantum communication systems. Based on already proposed error correction schemes, two new schemes are proposed, one for systems that employs polarization of singlephoton light, and other for systems that employs polarization of two-mode coherent states, being the first active, that is, requiring a control and synchronism protocol, while the second is passive. At last, it is realized a security analysis of a quantum key distribution system, employing the proposed error correction scheme, when the same is under Fuch-Peres-Brandt attack. It is shown that using the proposed error correction scheme the presence of an eavesdropper monitoring the quantum channel is more visible.
We present a quantum analysis of two-mode single-photon states based on the probability distributions of the optical field strength (or position quadrature) in order to describe their quantum polarization characteristics, where polarization is understood as a significative confinement of the optical field-strength values on determined regions of the two-mode optical field-strength plane. We will show that the mentioned probability distributions along with the values of quantum Stokes parameters allow us to characterize the polarization of a two-mode single-photon state, in an analogous way to the classical case, and to distinguish conceptually between mixture and partially polarized quantum states; in this way, we propose a simple definition of the quantum polarization degree based on the recent concept of distance measure to an unpolarized distribution, which gives rise to a depolarization degree equivalent to an overlapping between the probability distribution of the quantum state and a non-polarized two-mode Gaussian distribution. The work is particularly intended to university physics teachers and graduate students as well as to physicists and specialists concerned with the issue of optical polarization.
This study investigates quantum polarization in a two-mode generalized binomial state (TMGBS), a non-classical property of light, using quantum Stokes parameters and crucial in terms of its relationship to the purity and coherence of quantum states. Here we explore the criterion of quantum polarization in a generalized binomial state of light, which features a binomial photon number distribution in light pulses. Previous work by our group has examined other higher-order nonclassicality in single-and two-mode systems of GBS. Here we focus on the degree of polarization, an essential factor for observing entanglement in two-mode quantum states. Our findings emphasize the role of quantum polarization in detecting entanglement between optical modes, a fundamental resource for quantum communication protocols, including quantum teleportation and cryptography. The study demonstrates that TMGBS is an optimal candidate for achieving high degrees of quantum polarization under varied parameters, providing insights that could advance quantum technologies like quantum communication and metrology, where entanglement is pivotal.
The classical analogues of quantum correlations have been the subject of considerable interest in the past few years; however, all of these investigations consider the classical analogue of only pure quantum mechanical states. In this work, we study mixed classical light states and derive relations between the polarization coherence of the field and the (classical) entanglement between its degrees of freedom. We show, for a specific model of mixed states, where the purity is determined by a single parameter, how the coherence shared between polarization and entanglement shrinks as the level of purity decreases. The sum of the square of polarization and entanglement remains constant, a behavior consistent with previous results [Phys. Rev. Lett.117, 153901 (2016)PRLTAO0031-900710.1103/PhysRevLett.117.153901] of pure states, even though the constant for the mixed-state case is now smaller in value.
A brief review of theoretical studies of the quantum state of polarization of light exhibiting the level of fluctuations in at least one of the Stokes parameters which is below the quantum noise limit is presented. Two approaches to generation of polarization-squeezed state of light are analyzed in detail: by propagating coherent radiation in a cubic nonlinear medium and by mixing radiation of two orthogonally polarized quadrature-squeezed modes. The degree of polarization of light is discussed. Other areas of quantum polarization optics, in particular, entanglement of quantum Stokes parameters and quantum polarization tomography, are also discussed.