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Item type:Publication, Coherence-based measurement of non-Markovian dynamics in an open quantum system(American Physical Society, 2020-01-21)We present a theoretical scheme and its experimental proof of principle for an open quantum system undergoing Markovian and non-Markovian evolutions. We exhibit these two regimes by diagnosing them with the relative entropy of coherence of two polarization qubits playing the roles of system and ancilla. These are initially prepared in a polarization maximally entangled state of a photon pair produced by spontaneous parametric down-conversion. We induce Markovian and non-Markovian regimes in the system's dynamics with the help of two auxiliary qubits, experimentally implemented by optical paths in a layout of Sagnac and Mach-Zehnder interferometers. We replicate system-environment interactions by means of an amplitude damping channel and a suitably designed inversion of it. In our scheme, one needs only two experimentally accessible parameters to achieve Markovian and non-Markovian regimes. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Non-Markovianity leading to coherence revivals in an open quantum system(World Scientific, 2020-10-01)Coherence and quantum correlations have been identified as fundamental resources for quantum information tasks. As recently shown, these resources can be interconverted. In multipartite systems, entanglement represents a prominent case among quantum correlations, one which can be activated from coherence. All this makes coherence a key resource for securing the operational advantage of quantum technologies. When dealing with open systems, decoherence hinders full exploitation of quantum resources. Here, we present a protocol that allows reaching the maximal achievable amount of coherence in an open quantum system. By implementing our protocol, or suitable variants of it, coherence losses might be fully compensated, thereby leading to coherence revivals. We provide an experimental proof of principle of our protocol through its implementation with an all-optical setup. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Synthesis and characterization of pure, two-qubit states encoded in path and polarization(IOP Publishing Ltd, 2021-08-01)We have designed and experimentally put to test a protocol to synthesize and characterize pure, two-qubit states encoded in polarization and momentum (path) of light beams. Because these degrees of freedom are common to both classical and quantum light, it was possible to implement our protocol with classical light, thereby offering an advantageous and versatile testing ground. The experimental setup is robust and does not require state-dependent scheme modifications. We exhibited the capabilities of our protocol by generating three types of two-qubit states: Bell states, states with variable phases, and states with variable amplitudes. - Some of the metrics are blocked by yourconsent settings
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.