1. Quantum Key Distribution (QKD)

QKD is a method to establish a shared secret cryptographic key between two parties with unconditional security, guaranteed by the laws of physics. Any attempt by an eavesdropper to intercept the key introduces detectable disturbances, alerting the legitimate users. Popular protocols include BB84 and E91.

2. Quantum Repeaters

Due to photon loss in optical fibers, direct quantum communication is limited to relatively short distances. Quantum repeaters are essential for extending quantum communication over long distances by using techniques like entanglement swapping and quantum error correction to re-establish quantum links without directly measuring the quantum information.

3. Quantum Internet

The vision of a Quantum Internet is a global network capable of distributing quantum information (e.g., entangled qubits) between any two points on Earth. This network would enable advanced applications far beyond what is possible with classical communication, such as distributed quantum computing and highly secure global communication.

The field is witnessing rapid progress:

• Long-Distance QKD: Significant strides have been made in extending QKD ranges over both optical fiber and free-space links, including satellite-to-ground demonstrations. Quantum communication satellites are now a reality, enabling intercontinental QKD networks.

• Quantum Network Development: Early prototypes of quantum networks are being built globally, connecting multiple quantum nodes to demonstrate entanglement distribution and foundational quantum internet functionalities.

• Device-Independent QKD: Research is progressing on Device-Independent QKD (DIQKD), which offers even stronger security guarantees by not relying on the internal workings of the devices themselves.

• Hybrid Quantum Communication: Integration of different quantum technologies (e.g., photonic and superconducting platforms) is being explored to create robust and scalable communication systems.

Quantum communication holds immense potential for various applications:

• Unconditionally Secure Communication: Protecting sensitive data for governments, financial institutions, and critical infrastructure against all forms of cyberattacks, including those from future quantum computers.

• Distributed Quantum Computing: Connecting multiple quantum processors to create a more powerful distributed quantum computer, overcoming the limitations of single-site quantum machines.

• Enhanced Sensing and Metrology: Using distributed entanglement to create quantum sensor networks capable of ultra-precise measurements across large areas.

• Quantum Cloud Services: Enabling secure access to quantum computing resources over a quantum network, allowing users to perform quantum computations remotely without compromising data privacy.

• Fundamental Science: Providing new platforms for exploring foundational questions in quantum mechanics, such as the nature of entanglement and non-locality over vast distances.

CQST is at the forefront of these developments, contributing to both the theoretical understanding and experimental realization of next-generation quantum communication systems.