The paper introduces a novel scheme called Twin-Field Quantum Key Distribution (TF-QKD) to overcome the rate-distance barrier in Quantum Key Distribution (QKD). Traditional QKD schemes, which rely on quantum repeaters, face significant challenges in increasing key rates and range due to physical limitations. TF-QKD employs phase-randomized optical fields generated at two distant locations, which are then combined at a central measuring station. These "twin" fields can be used to distill a quantum key, achieving a key rate that scales with the square root of the channel transmittance, similar to a quantum repeater. However, TF-QKD does not require quantum repeaters and can be implemented with current technology, making it feasible for long-distance secure communication. The scheme leverages phase randomization and decoy states to extend the distance of secure quantum communications, while maintaining the security of the key generation process. The authors demonstrate that TF-QKD can surpass the secret key capacity (SKC) bound for optical quantum channels, even at realistic parameters, and show that it can achieve key rates over 550 km of standard optical fiber. The key feature of TF-QKD is the doubling of the distance between Alice and Bob by using twin fields, which interfere on a beam splitter at a central station. The paper also discusses the technical challenges and experimental setup required to implement TF-QKD, including phase drift compensation and visibility measurements.The paper introduces a novel scheme called Twin-Field Quantum Key Distribution (TF-QKD) to overcome the rate-distance barrier in Quantum Key Distribution (QKD). Traditional QKD schemes, which rely on quantum repeaters, face significant challenges in increasing key rates and range due to physical limitations. TF-QKD employs phase-randomized optical fields generated at two distant locations, which are then combined at a central measuring station. These "twin" fields can be used to distill a quantum key, achieving a key rate that scales with the square root of the channel transmittance, similar to a quantum repeater. However, TF-QKD does not require quantum repeaters and can be implemented with current technology, making it feasible for long-distance secure communication. The scheme leverages phase randomization and decoy states to extend the distance of secure quantum communications, while maintaining the security of the key generation process. The authors demonstrate that TF-QKD can surpass the secret key capacity (SKC) bound for optical quantum channels, even at realistic parameters, and show that it can achieve key rates over 550 km of standard optical fiber. The key feature of TF-QKD is the doubling of the distance between Alice and Bob by using twin fields, which interfere on a beam splitter at a central station. The paper also discusses the technical challenges and experimental setup required to implement TF-QKD, including phase drift compensation and visibility measurements.