976 publications from this institution
No abstract is provided for this article.
Birefringent single-mode fibers with random polarization mode coupling and polarization dependent losses are considered. The effect of these losses on polarization mode dispersion (PMD) is computed. The relevant number is found to be the differential loss between both polarization modes over one coupling length. For polarizing fibers, the coupling length is of several kilometers, the relevant number is thus high, and the PMD is significantly reduced by the differential loss. For standard fibers, on the other hand, the coupling length is of several tens of meters, the relevant number is thus small and polarization dependent losses have a negligible effect on the PMD.
No abstract is provided for this article.
Some guidelines for the comparison of different quantum key distribution experiments are proposed. An improved 'plug & play' interferometric system allowing fast key exchange is then introduced. Self-alignment and compensation of birefringence remain. Original electronics implementing the BB84 protocol and allowing user-friendly operation is presented. Key creation with 0.1 photon per pulse at a rate of 486 Hz with a 5.4% QBER - corresponding to a net rate of 210Hz - over a 23 Km installed cable was performed.
No abstract is provided for this article.
A long-standing tradition, largely present in both the physical and the philosophical literature, regards the advent of (special) relativity -- with its block-universe picture -- as the failure of any indeterministic program in physics. On the contrary, in this paper, we note that upholding reasonable principles of finiteness of information hints at a picture of the physical world that should be both relativistic and indeterministic. We thus rebut the block-universe picture by assuming that fundamental indeterminacy itself should as well be regarded as a relational property when considered in a relativistic scenario. We discuss the consequence that this view may have when correlated randomness is introduced, both in the classical case and in the quantum one.
First, we present a Bell-type inequality for n qubits, assuming that m out of the n qubits are independent. Quantum mechanics violates this inequality by a ratio that increases exponentially with m. Hence an experiment on n qubits violating this inequality sets a lower bound on the number m of entangled qubits. Next, we propose a definition of maximally entangled states of n qubits. For this purpose we study five different criteria. Four of these criteria are found compatible. For any number n of qubits, they determine an orthogonal basis consisting of maximally entangled states generalizing the Bell states.
A generalization of the CHSH-Bell inequality to arbitrary many settings is presented. The singlet state of two spin 1 2 violates this inequality for all numbers of setting. In the limit of arbitrarily large number of settings, the violation tends to the finite ratio 4 π ≈1.27.
We review the formalism required to investigate the combined effects of polarization-mode dispersion (PMD) and polarization dependent losses (PDL) in optical fiber networks. The combination of PMD and PDL may lead to anomalous dispersion, which is not correctly described by a direct application of the Jones matrix eigenanalysis (JME) method. This calls for a careful assessment of PMD measurement methods in the presence of PDL. We also present a theoretical analysis of distortions in analog transmissions, and computer simulations of digital transmissions. These show that distributed PDL increases the power penalty of the transmission more than lumped PDL at the end of the channel.
In relativity there is space-time out there. In quantum mechanics there is entanglement. Entanglement manifests itself by producing correlations between classical events (e.g. the firing of some detectors) at any two space-time locations. If the locations are time-like separated, i.e. one is in the future of the other, then there is no specific difficulty to understand the correlations. But if the two locations are space-like separated, the problem is different. How can the two space-time locations out there know about what happens in each other without any sort of communication? If space-time really exists, the locations must do something like communicating. Or it was all set up at the Beginning. But the correlations depend also on the free choice of the experimentalists, one in each space-time location. This allowed John Bell to derive his inequality and the experimentalists to violate it, thus refuting the assumption that it was all set up at the beginning: the Correlations can't be explained by common causes.
Deeper insight leads to better practice. We show how the study of the foundations of quantum mechanics has led to new pictures of open systems and to a method of computation which is practical and can be used where others cannot. We illustrate the power of the new method by a series of pictures that show the emergence of classical features in a quantum world. We compare the development of quantum mechanics and of the theory of (biological) evolution.
The addition of polarization dependent losses to birefringent optical networks increases signal distortions. This increase is created by the interaction between polarization mode dispersion and polarization loss. It cannot be explained by either alone.
We present a unified formalism describing the Einstein–Podolsky–Rosen test using spin 12 particles, photons, and kaons. This facilitates the comparison with existing experiments using photons and kaons. It underlines the similarities between birefringence and polarization-dependent losses that affect experiments using optical fibers and mixing and decay that are intrinsic to the kaons. We also discuss the limitation these two characteristics impose on the testing of Bell’s inequality.
