A quantum network enables the secure information transfer between quantum nodes shared with quantum entanglement which can be constructed by the distribution of the continuous variable (CV) quantum entangled states. By keeping certain modes at the server’s station and sending other modes to the users at the distant station, a quantum network with space-separated nodes can be established. In reality, the loss involved in the distribution process affects the amount of entanglement between the users and the server. Here, we analyzed the entanglement distribution processes for the four-mode CV cluster states with different structures by sending different modes of the entangled states to the distant nodes. Our results show the decoherence rates of the entanglement between the server and users are different for the cluster states with different structures. Our results provide a reference for the construction of a quantum network with CV cluster states and may have other potential implementations in future quantum communication based on CV quantum entanglement.
A quantum network enables the secure information transfer between quantum nodes shared with quantum entanglement which can be constructed by the distribution of the continuous variable (CV) quantum entangled states. By keeping certain modes at the server’s station and sending other modes to the users at the distant station, a quantum network with space-separated nodes can be established. In reality, the loss involved in the distribution process affects the amount of entanglement between the users and the server. Here, we analyzed the entanglement distribution processes for the four-mode CV cluster states with different structures by sending different modes of the entangled states to the distant nodes. Our results show the decoherence rates of the entanglement between the server and users are different for the cluster states with different structures. Our results provide a reference for the construction of a quantum network with CV cluster states and may have other potential implementations in future quantum communication based on CV quantum entanglement.
Quantum network plays a vitally important role in the practical application of quantum information, which requires the deterministic entanglement distribution among multiple remote users. Here, we propose a feasible scheme to deterministically distribute quadripartite entanglement by continuous-variable (CV) polarization states. The quantum server prepares the quadripartite CV polarization entanglement and distributes them to four remote users via optical fiber. In this way, the measurement of CV polarization entanglement is local oscillation free, which makes the long distance entanglement distribution in commercial optical fiber communication networks possible. Furthermore, both the Greenberger-Horne-Zeilinger-like (GHZ-like) and cluster-like polarization entangled states can be distributed among four users by controlling the beam splitter network in quantum server, which are confirmed by the extended criteria for polarization entanglement of multipartite optical modes. The protocol provides the direct reference for experimental implementation and can be directly extended to quantum network with more users, which is essential for a metropolitan quantum network.
Quantum network allows communication among more than two users with quantum teleportation and high quantum fidelity enabled by non-classical resources. As one of the most versatile architectures, all users are connected mediated by the central station in the star topology network, leading to the realization of the information interconnection and interoperability. In this work, we experimentally demonstrate a 4-branch continuous variable (CV) quantum teleportation network with star topology by employing entangled sideband modes from one squeezed state of light. Here, multiple pairs of entangled sideband modes are distributed on demand to central station and four nodes, respectively. Each node linked to the network has its own communication channel with the central station, where the deterministic CV quantum teleportation protocol is implemented with the fidelities above 0.830.
Quantum information processing (QIP) opens new opportunities for high-performance computing, high-precision sensing, and secure communications. Among various QIP features, the entanglement is a unique one. To take full advantage of quantum resources, it will be necessary to interface quantum systems based on different encodings of information both discrete and continuous. The goal of this paper is to lay the groundwork for the development of a robust and efficient hybrid continuous variable-discrete variable (CV-DV) quantum network, enabling the distribution of a large number of entangled states over hybrid DV-CV multi-hop nodes in an arbitrary topology. The proposed hybrid quantum communication network (QCN) can serve as the backbone for a future quantum Internet, thus providing extensive long-term impacts on the economy and national security through QIP, distributed quantum computing, quantum networking, and distributed quantum sensing. By employing the photon addition and photon subtraction modules we describe how to generate the hybrid DV-CV entangled states and how to implement their teleportation and entanglement swapping through entangling measurements. We then describe how to extend the transmission distance between nodes in hybrid QCN by employing macroscopic light states, noiseless amplification, and reconfigurable quantum LDPC coding. We further describe how to enable quantum networking and distributed quantum computing by employing the deterministic cluster state concept introduced here. Finally, we describe how the proposed hybrid CV-DV states can be used in an entanglement-based hybrid QKD.
Continuous-variable (CV) cluster states are a universal quantum computing platform that has experimentally out-scaled qubit platforms by orders of magnitude. The implementation of CV cluster states uses multimode squeezed Gaussian states and fault tolerance thresholds for CV quantum computing have been predicted for realistic squeezing. An outstanding question has been whether any Gaussian state can be expressed as a cluster state. We show here that Gaussian states can present hidden entanglement, which is not captured by the corresponding cluster state graph and therefore invalidates this graph. Hidden entanglement vanishes in the infinite squeezing limit, which should therefore be used with extreme caution. We derive a general procedure to detect hidden entanglement in an arbitrary Gaussian state and validate it as a CV cluster state. These results are relevant to all experimental implementations of CV cluster states to date.
Continuous-variable (CV) cluster states are a universal quantum computing platform that has experimentally outscaled qubit platforms by orders of magnitude.Room-temperature implementation of CV cluster states has been achieved with quantum optics by using multimode squeezed Gaussian states.It has also been proven that fault tolerance thresholds for CV quantum computing can be reached at realistic squeezing levels.In this paper, we show that standard approaches to design and characterize CV cluster states can miss entanglement present in the system.Such hidden entanglement may be used to increase the power of a quantum computer but it can also, if undetected, hinder the successful implementation of a quantum algorithm.By a detailed analysis of the structure of Gaussian states, we derive an algorithm that reveals hidden entanglement in an arbitrary Gaussian state and optimizes its use for one-way quantum computing.
A study of the entanglement properties of Gaussian cluster states, proposed as a universal resource for continuous variable (CV) quantum computing is presented in this paper. The central aim is to compare mathematically idealized cluster states defined using quadrature eigenstates, which have infinite squeezing and cannot exist in nature, with Gaussian approximations that are experimentally accessible. Adopting widely used definitions, we first review the key concepts, by analysing a process of teleportation along a CV quantum wire in the language of matrix product states. Next we consider the bipartite entanglement properties of the wire, providing analytic results. We proceed to grid cluster states, which are universal for the qubit case. To extend our analysis of the bipartite entanglement, we adopt the entropic-entanglement width, a specialized entanglement measure introduced recently by Van den Nest et al (2006 Phys. Rev. Lett. 97 150504), adapting their definition to the CV context. Finally, we consider the effects of photonic loss, extending our arguments to mixed states. Cumulatively our results point to key differences in the properties of idealized and Gaussian cluster states. Even modest loss rates are found to strongly limit the amount of entanglement. We discuss the implications for the potential of CV analogues for measurement-based quantum computation.