Advanced Quantum Communication and Quantum Networks -- From basic research to future applications

TL;DR

The paper surveys the field of quantum information networks, from foundational encoding and decoding limits to physical carriers and channels for quantum data transfer. It contrasts classical and quantum information transfer, underscoring fundamental bounds such as the Holevo limit and no-cloning, and then details quantum-secure direct communication and multipartite entanglement schemes. The physical basis section maps carriers (photons, microwaves, spin, phonons) and channels (free-space, fiber, waveguides) and presents an experimental superconducting microwave state-transfer example that embodies a minimal quantum network. In applications, it outlines the quantum internet vision, security/dqc scenarios, and quantum elections, illustrating concrete protocols like QKD, DQC, BQC, oblivious transfer and traveling-ballot schemes. The article concludes by outlining near-term implementations and a roadmap to a scalable quantum internet, highlighting technological challenges (memories, transducers, repeaters, standardization) and the promising potential of hybrid architectures.

Abstract

Classical communication is the basis for many of our current and future technologies, such as mobile phones, video conferences, autonomous vehicles and particularly the internet. In contrast, quantum communication is governed by the laws of quantum mechanics. Due to this fundamental difference, it might offer enormous benefits for security applications, more precise measurements, faster computations, and many other fields of application by interconnecting different quantum devices, such as quantum sensors, quantum computers, or quantum memories. This review provides an overview of the specific properties of quantum information networks. This includes the interfaces between the classical and the quantum regime, the transmission of the quantum information by physical implementations, and potential future applications of quantum networks. We aim to provide a starting point based on fundamental concepts of quantum information processing for further research on a future quantum internet.

Figures (28)

• Figure 1: Scheme depicting the interface between classical and quantum information with purely quantum information processing and transfer via a quantum information channel. Classical information has to be encoded first into quantum information. To this end, various methods discussed in this section can be used and depend on the specific purpose. This encoded information then serves as initial state for some purely quantum unitary evolution $\hat{U}$ processing the encoded data. One example discussed in this section is quantum secure direct communication (QSDC). After processing, a final quantum state is achieved. Finally, this state is detected and classical information is recovered.
• Figure 2: The quotient $m/n = 1/(1-H(p))$ from Nayak's theorem as a function of the success probability $p$ in the range $(1/2,1]$. The value at $p=1$ is $1$, which tells us that a perfect decoding requires $m=n$.
• Figure 3: The upper bound on the quotient $m/(n+H(p))$ given by \ref{['eq:multiple_bits']} as a function of $p$ for $k=10$.
• Figure 4: Schematic representation of the quantum secure direct communication protocol (QSDC) for a bipartite qubit system. The two qubits of the bipartite state are sent to Alice and Bob respectively. Alice then encodes her information by acting with either no operation or one of the three Pauli operators on her qubit. The complete state of the system is then described by one of the four Bell states. She then sends her qubit to Bob, who performs a Bell measurement on the complete two qubit state to decode Alice's information. As soon as the entangled two qubit state is established among Alice and Bob, an eavesdropper (Eve) can only access the qubit sent by Alice. Since this qubit is in a maximally mixed state for either encoded state, Eve cannot gain any information about the operation performed by Alice.
• Figure 5: Schematic representation of the quantum secure direct communication protocol (QSDC) for a tripartite qubit system with two senders and one receiver. The three qubits of the tripartite state are sent to Alice, Bob and Charlie, respectively. Alice and Bob then each encode their information by acting with either no operation or one of the three Pauli operators on their respective qubit. Alice and Bob then send their qubits to Charlie, who performs a measurement on the complete three qubit state to decode the information.