The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
I Brizita Djordjevic - One of the best experts on this subject based on the ideXlab platform.
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Spatial modes-based physical-layer security
2016 18th International Conference on Transparent Optical Networks (ICTON), 2016Co-Authors: I Brizita Djordjevic, Xiaole SunAbstract:The growth of the Internet traffic does not appear to be levelling off any time soon and it is projected to continue to grow exponentially in the years to come. Although there are many proposals on how to deal with the incoming bandwidth capacity crunch, the security of optical networks seems to be almost completely neglected. By taping out the portion of DWDM signal, the huge amount of data can be compromised. Therefore, the security of future optical networks is becoming one of the major issues to be addressed sooner rather than later. To address the security issues of future optical networks the quantum key distribution (QKD) and chaotic cryptography have been proposed. To avoid the high cost of QKD, the properly designed fiber Bragg gratings (FBGs) as optical encryption devices have been advocated recently. In this invited paper, we follow a different strategy. It is well known that we can associate with a photon both spin angular momentum (SAM), related to polarization; and orbital angular momentum (OAM), related to azimuthal dependence of the complex electric field. Because the OAM eigenstates are orthogonal, this additional degree of freedom can be utilized for the physical-layer security in optical networks. Given that the spatial modes in spatial domain multiplexing (SDM) fibers such as few-mode fibers (FMFs), few-core fibers (FCFs), and few-mode-few-core fibers (FMFCFs) can be decomposed in terms of OAM Eigenkets, the OAM can be used to enable the physical-layer security in both fiber-optics- and free-space optics-based optical networks.
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Quantum few-mode fiber communications based on the orbital angular momentum
IEEE Photonics Technology Letters, 2013Co-Authors: Changyu Lin, I Brizita Djordjevic, Milorad CvijeticAbstract:We study a quantum few-mode fiber (FMF) communication scheme based\non orbital angular momentum (OAM) modes and applied quantum information\ntheory to develop the quantum FMF channel model and to calculate\nthe quantum channel capacity. We assume a strong mode-coupling regime\nin FMF and an imperfect generation of OAM modes. The quantum FMF\nchannel is modeled as a concatenation of many fiber sections describing\nthe OAM Eigenkets transitions as a Markov chain. The proposed model\nis suitable for the study of the multidimensional quantum key distribution\nand teleportation over FMFs. Numerical simulations are performed\nto demonstrate the ability of the model to determine the FMF output\ndensity state for a given input density state. It is shown that FMF\nquantum channel capacity decreases with distance in a strong coupling\nregime if OAM basekets are imperfectly generated.
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Quantum channel capacity for OAM based free-space optical communications
Proceedings of SPIE, 2012Co-Authors: I Brizita Djordjevic, Yequn ZhangAbstract:We study the channel capacity for orbital angular momentum (OAM) based quantum free-space optical communications. Inspired by recent demonstrations for OAM-based single-photon communication, we construct the quantum density operator in matrix form, based on OAM Eigenkets, and determine the quantum channel model suitable for study of the quantum communication over atmospheric turbulence channels. The quantum channel model is derived from OAM Eigenkets transition probabilities. By using this model we determine the OAM quantum channel capacity in the presence of atmospheric turbulence. The proposed quantum channel model is of high importance for future study of quantum error correction coding to extend the transmission distance and data rate of free-space quantum communications.
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On the quantum-channel capacity for orbital angular momentum-based free-space optical communications
Optics Letters, 2012Co-Authors: Yequn Zhang, I Brizita Djordjevic, Xin GaoAbstract:Inspired by recent demonstrations of orbital angular momentum-(OAM)-based single-photon communications, we propose two quantum-channel models: (i) the multidimensional quantum-key distribution model and (ii) the quantum teleportation model. Both models employ operator-sum representation for Kraus operators derived from OAM Eigenkets transition probabilities. These models are highly important for future development of quantum-error correction schemes to extend the transmission distance and improve date rates of OAM quantum communications. By using these models, we calculate corresponding quantum-channel capacities in the presence of atmospheric turbulence.
Xin Gao - One of the best experts on this subject based on the ideXlab platform.
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On the quantum-channel capacity for orbital angular momentum-based free-space optical communications
Optics Letters, 2012Co-Authors: Yequn Zhang, I Brizita Djordjevic, Xin GaoAbstract:Inspired by recent demonstrations of orbital angular momentum-(OAM)-based single-photon communications, we propose two quantum-channel models: (i) the multidimensional quantum-key distribution model and (ii) the quantum teleportation model. Both models employ operator-sum representation for Kraus operators derived from OAM Eigenkets transition probabilities. These models are highly important for future development of quantum-error correction schemes to extend the transmission distance and improve date rates of OAM quantum communications. By using these models, we calculate corresponding quantum-channel capacities in the presence of atmospheric turbulence.
Yequn Zhang - One of the best experts on this subject based on the ideXlab platform.
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Quantum channel capacity for OAM based free-space optical communications
Proceedings of SPIE, 2012Co-Authors: I Brizita Djordjevic, Yequn ZhangAbstract:We study the channel capacity for orbital angular momentum (OAM) based quantum free-space optical communications. Inspired by recent demonstrations for OAM-based single-photon communication, we construct the quantum density operator in matrix form, based on OAM Eigenkets, and determine the quantum channel model suitable for study of the quantum communication over atmospheric turbulence channels. The quantum channel model is derived from OAM Eigenkets transition probabilities. By using this model we determine the OAM quantum channel capacity in the presence of atmospheric turbulence. The proposed quantum channel model is of high importance for future study of quantum error correction coding to extend the transmission distance and data rate of free-space quantum communications.
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On the quantum-channel capacity for orbital angular momentum-based free-space optical communications
Optics Letters, 2012Co-Authors: Yequn Zhang, I Brizita Djordjevic, Xin GaoAbstract:Inspired by recent demonstrations of orbital angular momentum-(OAM)-based single-photon communications, we propose two quantum-channel models: (i) the multidimensional quantum-key distribution model and (ii) the quantum teleportation model. Both models employ operator-sum representation for Kraus operators derived from OAM Eigenkets transition probabilities. These models are highly important for future development of quantum-error correction schemes to extend the transmission distance and improve date rates of OAM quantum communications. By using these models, we calculate corresponding quantum-channel capacities in the presence of atmospheric turbulence.
S. Wickramasekara - One of the best experts on this subject based on the ideXlab platform.
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On the Representation of Intermediate States in the Velocity Basis
arXiv: High Energy Physics - Theory, 2002Co-Authors: S. WickramasekaraAbstract:Unstable state furnishes a semigroup irreducible representation of the Poincar\'e group. The state vector is represented by a superposition of energy Eigenkets. As a consequence of this superposition, the state vector can be transformed into the rest frame through {\it a} Lorentz transformation only when the Eigenkets are labeled by velocity variable, but not momentum variable. We also clarify the meaning of the velocity variable in the state vector with respect to the velocity derived from kinematical consideration of the scattering process.
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Resonance states from poles of the relativistic S-matrix
International Journal of Modern Physics A, 2002Co-Authors: H. Kaldass, Arno Bohm, S. WickramasekaraAbstract:A state vector description for relativistic resonances is derived from the first order pole of the jth partial S-matrix at the invariant square mass value in the second sheet of the Riemann energy surface. To associate a ket, called Gamow vector, to the pole, we use the generalized eigenvectors of the four-velocity operators in place of the customary momentum Eigenkets of Wigner, and we replace the conventional Hilbert space assumptions for the in- and out-scattering states with the new hypothesis that in- and out-states are described by two different Hardy spaces with complementary analyticity properties. The Gamow vectors have the following properties: (i) They are simultaneous generalized eigenvectors of the four velocity operators with real eigenvalues and of the self-adjoint invariant mass operator M =(Pμ Pμ)1/2 with complex eigenvalue . (ii) They have a Breit–Wigner distribution in the invariant square mass variable and lead to an exactly exponential law for the decay rates and probabilities.
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Relativistic Gamow Vectors I Derivation from Poles of the S-Matrix
arXiv: High Energy Physics - Theory, 2001Co-Authors: Arno Bohm, H. Kaldass, S. WickramasekaraAbstract:A state vector description for relativistic resonances is derived from the first order pole of the $j$-th partial $S$-matrix at the invariant square mass value $\sm_R=(m-i\Gamma/2)^2$ in the second sheet of the Riemann energy surface. To associate a ket, called Gamow vector, to the pole, we use the generalized eigenvectors of the four-velocity operators in place of the customary momentum Eigenkets of Wigner, and we replace the conventional Hilbert space assumptions for the in- and out-scattering states with the new hypothesis that in- and out-states are described by two different Hardy spaces with complementary analyticity properties. The Gamow vectors have the following properties: - They are simultaneous generalized eigenvectors of the four velocity operators with real eigenvalues and of the self-adjoint invariant mass operator $M=(P_\mu P^\mu)^{1/2}$ with complex eigenvalue $\sqrt{\sm_R}$. - They have a Breit-Wigner distribution in the invariant square mass variable $\sm$ and lead to an exactly exponential law for the decay rates and probabilities.
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Time asymmetric quantum theory and the ambiguity of the Z-boson mass and width
The European Physical Journal C - Particles and Fields, 2000Co-Authors: A. Bohm, H. Kaldass, N.l. Harshman, S. WickramasekaraAbstract:Relativistic Gamow vectors emerge naturally in a time asymmetric quantum theory as the covariant kets associated to the resonance pole $s=s_R$ in the second sheet of the analytically continued S -matrix. They are Eigenkets of the self-adjoint mass operator with complex eigenvalue $\sqrt{s_R}$ and have exponential time evolution with lifetime $\tau = - \hbar/2\mathrm{Im}\sqrt{s_R}$ . If one requires that the resonance width $\Gamma$ (defined by the Breit-Wigner lineshape) and the resonance lifetime $\tau$ always and exactly fulfill the relation $\Gamma=\hbar/\tau$ , then one is lead to the following parameterization of $s_R$ in terms of resonance mass $M_R$ and width $\Gamma_R$ : $s_R = (M_R - i\Gamma/2)^2$ . Applying this result to the $Z$ -boson implies that $M_R \approx M_Z - 26\mbox{MeV}$ and $\Gamma_R \approx \Gamma_Z-1.2\mbox{MeV}$ are the mass and width of the {\it Z}-boson and not the particle data values $(M_Z,\Gamma_Z)$ or any other parameterization of the Z -boson lineshape. Furthermore, the transformation properties of these Gamow kets show that they furnish an irreducible representation of the causal Poincaré semigroup, defined as a semi-direct product of the homogeneous Lorentz group with the semigroup of space-time translations into the forward light cone. Much like Wigner's unitary irreducible representations of the Poincaré group which describe stable particles, these irreducible semigroup representations can be characterized by the spin-mass values $(j,s_R=(M_R-i\Gamma/2)^2)$ .
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Time asymmetric quantum theory and the ambiguity of the Z-boson mass and width
European Physical Journal C, 2000Co-Authors: Arno Bohm, H. Kaldass, N.l. Harshman, S. WickramasekaraAbstract:Relativistic Gamow vectors emerge naturally in a time asymmetric quantum theory as the covariant kets associated to the resonance pole \(s=s_R\) in the second sheet of the analytically continued S-matrix. They are Eigenkets of the self-adjoint mass operator with complex eigenvalue \(\sqrt{s_R}\) and have exponential time evolution with lifetime \(\tau = - \hbar/2\mathrm{Im}\sqrt{s_R}\). If one requires that the resonance width \(\Gamma\) (defined by the Breit-Wigner lineshape) and the resonance lifetime \(\tau\) always and exactly fulfill the relation \(\Gamma=\hbar/\tau\), then one is lead to the following parameterization of \(s_R\) in terms of resonance mass \(M_R\) and width \(\Gamma_R\): \(s_R = (M_R - i\Gamma/2)^2\). Applying this result to the \(Z\)-boson implies that \(M_R \approx M_Z - 26\mbox{MeV}\) and $\Gamma_R \approx \Gamma_Z-1.2\mbox{MeV}$ are the mass and width of the {\it Z}-boson and not the particle data values \((M_Z,\Gamma_Z)\) or any other parameterization of the Z-boson lineshape. Furthermore, the transformation properties of these Gamow kets show that they furnish an irreducible representation of the causal Poincare semigroup, defined as a semi-direct product of the homogeneous Lorentz group with the semigroup of space-time translations into the forward light cone. Much like Wigner's unitary irreducible representations of the Poincare group which describe stable particles, these irreducible semigroup representations can be characterized by the spin-mass values \((j,s_R=(M_R-i\Gamma/2)^2)\).
Milorad Cvijetic - One of the best experts on this subject based on the ideXlab platform.
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Quantum few-mode fiber communications based on the orbital angular momentum
IEEE Photonics Technology Letters, 2013Co-Authors: Changyu Lin, I Brizita Djordjevic, Milorad CvijeticAbstract:We study a quantum few-mode fiber (FMF) communication scheme based\non orbital angular momentum (OAM) modes and applied quantum information\ntheory to develop the quantum FMF channel model and to calculate\nthe quantum channel capacity. We assume a strong mode-coupling regime\nin FMF and an imperfect generation of OAM modes. The quantum FMF\nchannel is modeled as a concatenation of many fiber sections describing\nthe OAM Eigenkets transitions as a Markov chain. The proposed model\nis suitable for the study of the multidimensional quantum key distribution\nand teleportation over FMFs. Numerical simulations are performed\nto demonstrate the ability of the model to determine the FMF output\ndensity state for a given input density state. It is shown that FMF\nquantum channel capacity decreases with distance in a strong coupling\nregime if OAM basekets are imperfectly generated.