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IEEE Journal of Quantum Electronics

Quantum Theory Analysis of Loss Effects in Guided Nonlinear-Optic Twin-Photon Generation

Toshiaki Suhara, T. Nosaka

Published Jul 21, 2006• 7 citations
Publisher

Abstract

Integrated nonlinear-optic (NLO) devices for generation of twin-photon beams are a key device for quantum information techniques. This paper presents a quantum theory analysis on the effect of optical losses in twin-photon generation. The analysis uses a multi-mode-pair description, and is based upon unitary transformations of amplitude operators and state vectors for describing the NLO and loss phenomena in infinitesimal sections in the interaction range. Full description of the quantum states of the twin-photon beams affected by the losses is obtained. Mathematical expressions useful for prediction of the performances degradation are deduced

DOI
10.1109/jqe.2006.877219

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Loss is inevitable for the optical system due to absorption of materials, scattering caused by the defects and surface roughness. In quantum optical circuits, the loss can not only reduce the intensity of signal, but also affect the performance of quantum operations. In this work, we divide losses into unbalanced linear loss and shared common loss, and provide a detailed analysis on how loss affects the integrated linear optical quantum gates. It is found that the orthogonality of eigenmodes and the unitary phase relation of the coupled waveguide modes are destroyed by the loss. As a result, the fidelity of single- and two-qubit operations decrease significant as the shared loss becomes comparable to the coupling strength. Our results are important for the investigation of large-scale photonic integrated quantum information process.
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.
Integrated nonlinear waveguide structures enable generation of quantum entangled photons. We describe theoretically the effects of spatially inhomogeneous loss on the creation of photon pairs through spontaneous parametric down-conversion in quadratically nonlinear directional couplers, where photons experience effective parity-time (PT) symmetric potential due to the presence of optical loss in one of the waveguides. We show that for losses below the PT-breaking threshold, the quantum photon states can be flexibly tuned similarly to conservative couplers, whereas for stronger losses, the correlations between two waveguide modes are suppressed. We also formulate a quantum-classical correspondence with sum-frequency generation for fast evaluation of device performance. These results can be applied for the design of quantum plasmonic circuits.
Abstract This paper reviews the quasi‐phase‐matched (QPM) waveguide nonlinear‐optic device technologies for generation of quantum‐entangled twin photons indispensable for quantum‐information techniques. After a brief introduction to the concept of entanglement, quantum theory analysis of twin‐photon generation (TPG) is outlined to clarify the properties of twin photons. Then, methods for entangled‐photon generation are discussed. Practical design and theoretical performances of LiNbO3 waveguide QPM TPG devices, as well as the fabrication techniques, are described. Finally, experimental demonstrations of polarization‐entangled twin‐photon generation by waveguide Type‐I and Type‐II QPM TPG devices are presented.