[Paper Review] Quantum key distribution based on entanglement swapping

Adán Cabello|arXiv (Cornell University)|Nov 6, 1999

Quantum Information and Cryptography3 citations

TL;DR

This paper proposes a quantum key distribution (QKD) protocol using entanglement swapping between three Einstein-Podolsky-Rosen (EPR) pairs to generate a shared secret key between distant parties. By enabling remote correlation of measurement outcomes via Bell-state measurements, the scheme enhances key generation rates, reduces required qubit sequences, and lowers the number of bits needed to detect eavesdropping, with entanglement as a fundamental resource.

ABSTRACT

Entanglement swapping between EPR pairs can be used to generate the same sequence of random bits in two remote places. A quantum key distribution protocol based on this idea is described. The scheme exhibits the following features: (a) It improves the rate of generated bits for transmitted qubit. (b) It allows Alice and Bob to generate a key of arbitrary length using a single quantum system (three EPR pairs), instead of a long sequence of them. (c) Detecting Eve requires the comparison of fewer bits. (d) Entanglement is an essential ingredient. The scheme assumes reliable measurements of the Bell operator.

Motivation & Objective

• To develop a QKD protocol that leverages entanglement swapping to generate correlated random bits at remote locations.
• To improve the rate of key generation per transmitted qubit compared to standard entanglement-based QKD protocols.
• To enable the creation of arbitrarily long keys using only three EPR pairs, eliminating the need for long sequences of entangled particles.
• To reduce the number of classical bits required for eavesdropping detection by minimizing comparison overhead.
• To establish entanglement as an essential resource in the protocol's security and functionality.

Proposed method

• Entanglement swapping is performed on three EPR pairs shared among three parties: Alice, Bob, and a third party (or a relay).
• Bell-state measurements are conducted on one particle from each of two EPR pairs to project the remaining two particles into an entangled state.
• The resulting entanglement between the two remote particles (one with Alice and one with Bob) enables them to generate identical random bit sequences through correlated measurement outcomes.
• The protocol relies on reliable measurement of the Bell operator to verify entanglement and detect any disturbance by an eavesdropper.
• Classical communication is used to compare measurement bases and identify correlated outcomes, forming the basis of the shared key.
• The scheme ensures security by detecting any deviation from expected Bell-state correlations, indicating potential eavesdropping.

Experimental results

Research questions

• RQ1 Can entanglement swapping be used to generate a shared secret key between two remote parties without direct entanglement between them?
• RQ2 How does the key generation rate of this protocol compare to standard entanglement-based QKD schemes in terms of transmitted qubits?
• RQ3 To what extent can the key length be extended using only three EPR pairs instead of a long sequence?
• RQ4 What is the minimum number of classical bits required for eavesdropping detection in this scheme compared to conventional protocols?
• RQ5 How does the reliance on Bell operator measurements affect the protocol's security and feasibility?

Key findings

• The protocol achieves a higher rate of key generation per transmitted qubit compared to standard entanglement-based QKD protocols.
• A single quantum system consisting of three EPR pairs can generate a key of arbitrary length, eliminating the need for long sequences of entangled particles.
• The number of classical bits required for eavesdropping detection is reduced, as fewer outcomes need to be compared.
• Entanglement is a necessary and essential ingredient for the protocol's operation and security.
• Reliable measurement of the Bell operator is critical for verifying entanglement and detecting eavesdropping attempts.