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Here, we review the basic concepts and applications of the phase-field-crystal (PFC) method, which is one of the latest simulation methodologies in materials science for problems, where atomic- and microscales are tightly coupled. The PFC…

Spontaneous parametric down-conversion (SPDC) is a widely used process to prepare entangled photon pairs. In SPDC, a second-order nonlinear crystal is pumped by a coherent laser beam to generate photon pairs. The photon pairs are usually…

Quantum Physics · Physics 2024-09-16 Richard Bernecker , Baghdasar Baghdasaryan , Stephan Fritzsche

Entanglement of high dimensional states is becoming increasingly important for quantum communication and computing. The most common source of entangled photons is spontaneous parametric down conversion (SPDC), where the degree of frequency…

Quantum Physics · Physics 2020-01-22 C. Okoth , E. Kovlakov , F. Boensel , A. Cavanna , S. Straupe , S. P. Kulik , M. V. Chekhova

Hyper-entanglement between two or more photonic degrees of freedom (DOF) can enhance and enable new quantum protocols by allowing each DOF to perform the task it is optimally suited for. Here we demonstrate the generation of photon pairs…

Hybridizing different physical systems or degrees of freedom offers significant advantages for realizing practical, universal, scalable, and fault-tolerant quantum computation (FTQC). Here, we propose optical FTQC schemes with low squeezing…

Quantum Physics · Physics 2025-03-27 Peilin Du

Strongly-driven nonlinear optical processes such as spontaneous parametric down-conversion and spontaneous four-wave mixing can produce multiphoton nonclassical beams of light which have applications in quantum information processing and…

A highly attenuated laser pulse which gives a weak coherent state is widely used in quantum key distribution (QKD) experiments. A weak coherent state has multi-photon components, which opens up a security loophole to the sophisticated…

Quantum Physics · Physics 2008-08-12 Xiongfeng Ma

Photonic integrated circuits (PICs) are expected to play a significant role in the ongoing second quantum revolution, thanks to their stability and scalability. Still, major upgrades are needed for available PIC platforms to meet the…

Integrated photonics computing has emerged as a promising approach to overcome the limitations of electronic processors in the post-Moore era, capitalizing on the superiority of photonic systems. However, present integrated photonics…

Optics · Physics 2023-08-15 Yuepeng Wu , Hongxiang Guo , Bowen Zhang , Jifang Qiu , Zhisheng Yang , Jian Wu

Mean-field treatment (MFT) is frequently applied to approximately predict the dynamics of quantum optics systems, to simplify the system Hamiltonian through neglecting certain modes that are driven strongly or couple weakly with other…

Quantum Physics · Physics 2023-12-19 Yue-Xun Huang , Ming Li , Zi-Jie Chen , Xu-Bo Zou , Guang-Can Guo , Chang-Ling Zou

Schr\"odinger-cat (SC) states are an important resource for continuous-variable quantum computing and quantum metrology. In our previous work [JOSA B, 42, 2 (2025)], we proposed a probabilistic protocol for generating bright squeezed SC…

Quantum Physics · Physics 2026-03-26 V. L. Gorshenin

The U(1,1) and U(2) transformations realized by three-mode interaction in the respective parametric approximations are studied in conditional measurement, and the corresponding non-unitary transformation operators are derived. As an…

Quantum Physics · Physics 2016-04-05 J. Clausen , H. Hansen , L. Knoll , J. Mlynek , D. -G. Welsch

Photosystem II (PSII) reaction center is a unique protein-chromophore complex that is capable of efficiently separating electronic charges across the membrane after photoexcitation. In the PSII reaction center, the primary energy- and…

With advanced micro- and nano-photonic structures, the vacuum photon-photon coupling rate is anticipated to approach the intrinsic loss rate and lead to unconventional quantum effects. Here, we investigate the classical-to-quantum…

Quantum Physics · Physics 2022-04-11 Yue-Xun Huang , Ming Li , Ke Lin , Yan-Lei Zhang , Guang-Can Guo , Chang-Ling Zou

High-rate entanglement generation is essential for the realization of practical quantum repeaters. To this end, frequency multiplexing of the photons employed is an effective approach. In particular, schemes using cavity-enhanced…

Quantum Physics · Physics 2026-04-02 Ryoma Komatsudaira , Tomoyuki Horikiri

Orthogonal frequency-division multiplexing (OFDM) has been selected as the basis for the fifth-generation new radio (5G-NR) waveform developments. However, effective signal processing tools are needed for enhancing the OFDM spectrum in…

Signal Processing · Electrical Eng. & Systems 2024-10-30 Juha Yli-Kaakinen , AlaaEddin Loulou , Toni Levanen , Kari Pajukoski , Arto Palin , Markku Renfors , Mikko Valkama

The use of quantum bits (qubits) in cryptography holds the promise of secure cryptographic quantum key distribution schemes. It is based usually on single-photon polarization states. Unfortunately, the implemented ``qubits'' in the usual…

Quantum Physics · Physics 2015-05-06 Gilles Brassard , Tal Mor , Barry C. Sanders

Multi-photon hyperentangement is of fundamental importance in optical quantum information processing. Existing theory and experiment producing multi-photon hyperentangled states have until now relied on the outcome post-selection, a…

Photon sources based on spontaneous parametric down-conversion (SPDC) are central to experimental quantum optics and quantum technologies. Their performance is commonly quantified by three metrics: pair-collection probability, heralding…

Quantum Physics · Physics 2026-02-27 Carlos Sevilla-Gutiérrez , Varun Raj Kaipalath , Fabian Steinlechner

Time-frequency Schmidt (TFS) modes of ultrafast quantum states are naturally compatible with high bit-rate integrated quantum communication networks. Thus they offer an attractive alternative for the realization of high dimensional quantum…