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arXiv:0906.5387 · The European Physical Journal D

Photon losses depending on polarization mixedness

Laleh Memarzadeh, Stefano Mancini

Published Nov 6, 2009• 2 citations
arXivHTMLPDF
DOI
10.1140/epjd/e2009-00278-2

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We have developed a “digital twin” of the photon entanglement generation process to model the degradation of quantum entangled states produced via spontaneous parametric down-conversion (SPDC) when transmitted through lossy and noisy optical channels. These two-mode entangled states can exhibit entanglement in photon number, polarization, and spectral-temporal modes, making them valuable resources for quantum communication and information processing. Using a density matrix formalism, we perform numerical simulations to model the interaction of each mode with its environment, incorporating the effects of photon loss, incoherent noise processes, and intermodal correlations between polarization and frequency degrees of freedom. Purity and fidelity are key metrics used to quantify the mixedness and coherence of the transmitted state. The simulation results quantify the decoherence as noise and loss increase, highlighting the vulnerability of entanglement to environmental disturbances and the compounding impact of mode-dependent quantum correlations. This study provides insight into the performance limits of SPDC-based entangled photon sources and offers guidance for optimizing quantum systems operating under realistic conditions. The simulation platform serves as a predictive tool, enabling future integration with experimental control systems and benchmarking against measured entangled photon characteristics such as Hong-Ou-Mandel interference and polarization correlation visibility.
Abstract The intrinsic decoherence effects on a flux qubit coupled to a resonator through a two-photon interaction where the resonator field is initially in coherent and even coherent states are investigated. The qubit-resonator entanglement and coherence loss (mixedness) of the system and its subsystems are examined using entropy and negativity. The ability of the qubit-resonator interaction to generate quantum coherence (qubit-resonator entanglement and mixedness) is shown to be dependent on the initial cavity non-classicality, detuning, and decoherence. For larger values of the qubit-resonator detuning, the initial resonator non-classicality can enhance the generation and stability of quantum coherence. The decoherence degrades the qubit-resonator entanglement and destroys the sudden death-birth entanglement.
We report a controllable method for producing mixed two-photon states via spontaneous parametric down-conversion with a two-type-I crystal geometry. By using variable polarization rotators (VPRs), one obtains mixed states of various purities and degrees of entanglement depending on the parameters of the VPRs. The generated states are characterized by quantum state tomography. The experimental results are found to be in good agreement with the theory. The method can be easily implemented for various experiments that require the generation of states with controllable degrees of entanglement or mixedness.