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Item type:Publication, Constraints between concurrence and polarization for mixed states subjected to open system dynamics(American Physical Society, 2022-06-01)Entanglement and polarization are mutually constrained by the relationship ${C}^{2}+{P}^{2}=1$, which engages the concurrence $C$ of a pure, two-qubit state and the degree of polarization $P$ of either of its two subsystems. How the above constraint generalizes for mixed states is an open question. We address mixed, two-qubit states of the $X$ type, i.e., those whose density matrix has nonzero elements only in the two main diagonals. We focus on mixed states that arise out of a pure, two-qubit state that is subjected to either the amplitude damping channel or the depolarizing channel. We derive alternative constraints for concurrence and polarization and test them experimentally with polarization-entangled photons. We argue that our theoretical results hold also for classical light, whenever two binary degrees of freedom can be entangled. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Relationship between entanglement and polarization in tripartite states(Institute of Physics, 2022-10-01)Entanglement and polarization of pure, two-qubit systems are known to be constrained by the relationship C 2 + P 2 = 1 . Here, C stands for concurrence, a standard measure of entanglement, and P refers to the degree of polarization of either of the two, single-qubit subsystems. The above constraint may be understood as reflecting that a system cannot be in a pure state, if it is entangled with another one. In order to explore the connection between entanglement and polarization beyond two-qubit systems, we addressed states in which at least one of the parties has dimensionality greater than two. The case of pure, tripartite states offered itself as a timely candidate. We focussed on three qubits and studied the connection between one qubit’s polarization and its entanglement with the other two taken together. We derived new constraints, akin to the above one, and submitted them to experimental tests using single photons entangled in polarization. The latter provided two qubits, each one attached to one photon. The third qubit was chosen to be the path (momentum) of one of the photons. Our experimental results confirmed the validity of the new constraints. Our theoretical results hold also for classical light. Possible experimental tests could be done with so-called structured light beams. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Stokes vector characterization by strongly measuring weak values(Optica Publishing Group (formerly OSA), 2024-04-01)We report the implementation of a non-standard procedure to perform Stokes polarimetry, which was recently proposed by considering weak value measurements. Our procedure is not restricted to weak measurements but applies for both weak and strong couplings between the observable being measured; the polarization (spin) vector; and the measuring device, the “pointer.” In optics, the polarization-pointer coupling is usually implemented with a birefringent crystal. This applies in the weak coupling regime. We overcame this limitation by using an alternative setup in which one can go from weak to strong couplings by tuning a moveable mirror. We carried out our proof-of-concept experiments with a laser beam, the image of which was recorded and processed on a charge-coupled device. Our results illustrate that some concepts, originally introduced in a quantum context, in fact refer to properties that are common to both quantum and classical phenomena. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Wave–Particle Duality in Tripartite Systems(Optica Publishing Group (formerly OSA), 2023-04-01)Quantum objects, sometimes called quantons, often display a characteristic feature referred to as wave–particle duality (WPD). Lately, this and other quantum traits have been subjected to intensive research, mainly motivated by the development of quantum information science. As a consequence, the scopes of some concepts have been extended, and it has been realized that they are not in the exclusive domain of quantum physics. This is particularly clear in optics, where qubits may show up as Jones vectors and WPD has its counterpart as wave–ray duality. WPD was originally addressed by focusing on a single qubit, which was afterwards supplemented with a second one playing the role of a path-marker in an interferometer setup. Fringe contrast, a sign of wave-like behavior, was proved to be diminished in connection with the effectiveness of the marker, the inducer of particle-like behavior. Going from bipartite to tripartite states is a natural and necessary step towards better understanding of WPD. This step is what we have accomplished in this work. We report some constraints ruling WPD for tripartite systems, as well as their experimental display with single photons.