Covert Entanglement Transmission Achieved Reliably Through Noisy Quantum Channels.

Research demonstrates covert entanglement generation is possible across noisy communication channels, specifically bosonic channels which model microwave and radio frequencies. A single-letter expression defines optimal rates for reliably generating entangled bits while remaining undetectable to adversaries, with analysis extending to photonic qubit implementations.

The secure transmission of information relies increasingly on the principles of quantum mechanics, yet practical implementations often face challenges from signal loss and environmental noise. Recent research addresses the possibility of establishing quantum entanglement, a key resource for quantum communication, in a manner undetectable to potential eavesdroppers. This is achieved through a process termed ‘covert communication’, where signals are deliberately masked within the inherent noise of the communication channel. A team comprising Evan J. D. Anderson, Michael S. Bullock, Ohad Kimelfeld, Christopher K. Eyre, Filip Rozpędek, Uzi Pereg, and Boulat A. Bash detail their findings in a study titled ‘Covert Entanglement Generation over Bosonic Channels’. Their work explores the theoretical limits of covert entanglement generation across bosonic channels, which model a wide range of physical systems including mechanical, microwave, and radio-frequency communication links, and proposes achievable methods for establishing secure quantum links even in noisy environments. The team demonstrates the possibility of generating entangled bits, or ‘ebits’, covertly and reliably, offering a pathway towards practical, secure quantum communication networks.

Research demonstrates the feasibility of generating covert entanglement across noisy communication channels, a development with implications for secure quantum communication networks. The study focuses on lossy bosonic channels, systems where signals degrade with distance and are subject to thermal noise – random fluctuations caused by temperature – relevant to technologies employing superconducting circuits, microwaves, and radio frequencies. Researchers establish that secure entanglement, quantified in entangled bits (ebits), can be reliably created covertly using a defined number of channel transmissions.

The core of the work lies in defining a single mathematical expression, a ‘single-letter expression’, that determines the maximum rate at which entanglement can be generated. This simplifies the complex calculations previously required to analyse and design covert quantum communication systems. Crucially, the research establishes a ‘rate region’ for covert entanglement, proving that entanglement can be generated without alerting a potential eavesdropper. This is achieved by concealing the signal within the inherent noise of the channel, ensuring the confidentiality of the quantum information being transmitted.

Calculations reveal the achievable entanglement rate is directly linked to channel characteristics, specifically the degree of signal loss and the level of thermal noise. This establishes a quantifiable trade-off between the speed of communication and the level of security, providing valuable data for optimising communication strategies in real-world scenarios. Understanding this relationship allows for the tailoring of communication protocols to specific channel conditions, maximising both efficiency and security.

The analysis further extends to consider the practical implications of different methods for encoding quantum information. The study compares the performance of ‘single-rail’ and ‘dual-rail’ photonic qubits. Single-rail encoding represents a quantum bit, or qubit, using a single photon of light, while dual-rail encoding utilises two photons. The latter offers potentially improved resilience to noise, enhancing the reliability of quantum information transmission. The investigation demonstrates how the choice of encoding impacts the efficiency of covert communication, providing guidance for selecting the optimal scheme for specific implementations and contributing to the development of robust and efficient quantum communication technologies.