Résultats de recherche pour « Hyperentanglement »

Abstract Characterizing a high-dimensional entanglement is fundamental in quantum information applications. Here, we propose a theoretical scheme to analyze and characterize the angular momentum hyperentanglement that two photons are entangled simultaneously in spin and orbital angular momentum. Based on the electro-optic sampling with a proposed hyper-entanglement analyzer and the simple matrix operation using Cramer rule, our simulations show that it is possible to retrieve effectively both the information about the degree of polarization entanglement and the spiral spectrum of high-dimensional orbital angular momentum entanglement.

Abstract Quantum secure direct communication (QSDC) can directly transmit confidential messages without pre-distributing secret keys. In practical applications, non-ideal light sources naturally contain multiphoton components, which can easily lead to photon-number-splitting attacks and constitute a core problem restricting secure practical implementation. Existing measurement-device-independent (MDI) QSDC protocols are mostly based on ideal source assumptions and lack strict security authentication for practical multiphoton risks. This paper proposes an MDI-QSDC protocol based on decoy states and polarization--spatial hyperentanglement. The protocol lower-bounds the contribution of the two-single-pair sector through an active three-intensity decoy-state mechanism and imposes a conservative bound on the potential information leakage caused by multiphoton events, while using polarization--spatial hyperentangled encoding to increase the payload of each valid HBSA event and relying on the MDI architecture to remove the need to trust the measurement device. Compared with similar schemes, this protocol significantly improves the secure message capacity in practical scenarios while maintaining detector-side security.

Abstract Implementing CNOT operation nonlocally is one of central tasks in distributed quantum computation. Most of previously protocols for implementation quantum CNOT operation only consider implement CNOT operation in one degree of freedom(DOF). In this paper, we present a scheme for nonlocal implementation of hyper-parallel CNOT operation in polarization and spatial-mode DOFs via hyperentanglement. The CNOT operations in polarization DOF and spatial-mode DOF can be remote implemented simultaneously with hyperentanglement assisited by cross-Kerr nonlinearity. Hyper-parallel nonlocal CNOT gate can enhance the quantum channel capacity for distributed quantum computation and long-distance quantum communication. We discuss the experiment feasibility for hyper-parallel nonlocal gate. It shows that the protocol for hyper-parallel nonlocal CNOT operation can be realized with current technology.