Entanglement Effects in Highly Dense Systems

Časlav Brukner, Vlatko Vedral, Anton Zeilinger

Shang‐Yu Ren, Wei-Qiang Wang, Yujie Cheng +7 more

Abstract The dense quantum entanglement distribution is the basis for practical quantum communication, quantum networks and distributed quantum computation. To make entanglement distribution processes stable enough for practical and large-scale applications, it is necessary to perform them with the integrated pattern. Here, we first integrate a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers on one large-scale photonic chip and demonstrate the multi-channel wavelength multiplexing entanglement distribution among distributed photonic chips. Specifically, we use one chip as a sender to produce high-performance and wideband quantum photon pairs, which are then sent to two receiver chips through 1-km standard optical fibers. The receiver chip includes a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers and realizes multi-wavelength-channel energy-time entanglement generation and analysis. High quantum interference visibilities prove the effectiveness of the multi-chip system. Our work paves the way for practical entanglement-based quantum key distribution and quantum networks.

Mansour F. Yassen, Emad K. Jaradat, Altahir Saad +1 more

ABSTRACT High‐dimensional quantum systems offer a promising pathway to exceed information capacity limits, yet realizing robust dense coding remains challenged by decoherence. While Floquet engineering allows dynamic control, its potential in high‐spin systems is not fully exploited. Here, presenting a novel integration of periodic driving with higher‐dimensional thermal spin models, we investigate the dense coding capacity of a two‐qutrit Heisenberg XXZ system with single‐ion anisotropy. By deriving an effective Hamiltonian, we analyze the effect of the external driving parameters on the system's quantum resources. We demonstrate capacity modulation via the Floquet driving ratio, where renormalization factor zeros induce dynamical decoupling, suppressing quantum advantage. Crucially, negative single‐ion anisotropy amplifies quantum efficiency gain to approximately 95% relative to the classical limit, offering resilience against thermal fluctuations. Furthermore, we numerically demonstrate a monotonic, nonlinear parametric dependence between capacity and negativity, revealing a critical entanglement threshold required to surpass the classical Holevo bound. These results provide a blueprint for designing tunable, high‐capacity quantum channels, highlighting anisotropy as a pivotal control parameter.

Hsuan‐Hao Lu, Muneer Alshowkan, Karthik V. Myilswamy +3 more

We generate ultrabroadband photon pairs entangled in both polarization and frequency bins through an all-waveguided Sagnac source covering the entire optical C- and L-bands (1530-1625 nm). We perform comprehensive characterization of high-fidelity states in multiple dense wavelength-division multiplexed channels, achieving full tomography of effective four-qubit systems. Additionally, leveraging the inherent high dimensionality of frequency encoding and our electro-optic measurement approach, we demonstrate the scalability of our system to higher dimensions, reconstructing states in a 36-dimensional Hilbert space consisting of two polarization qubits and two frequency-bin qutrits. Our findings hold potential significance for quantum networking, particularly dense coding and entanglement distillation in wavelength-multiplexed quantum networks.

Jenny Hide, Vlatko Vedral