[Paper Review] Quantum bit commitment protocol without quantum memory

Rubens Viana Ramos, Fábio Alencar Mendonça|ArXiv.org|Jan 4, 2008

Quantum Information and Cryptography10 references3 citations

TL;DR

This paper proposes a quantum bit commitment protocol that eliminates the need for quantum memory, enabling implementation with current experimental technology. By using prepare-and-measure techniques with single-photon states and time-bin encoding, the protocol achieves a level of security superior to classical bit commitment, marking a significant step toward practical quantum cryptography without requiring quantum storage.

ABSTRACT

Quantum protocols for bit commitment have been proposed and it is largely accepted that unconditionally secure quantum bit commitment is not possible; however, it can be more secure than classical bit commitment. In despite of its usefulness, quantum bit commitment protocols have not been experimentally implemented. The main reason is the fact that all proposed quantum bit commitment protocols require quantum memory. In this work, we show a quantum bit commitment protocol that does not require quantum memory and can be implemented with present technology.

Motivation & Objective

• To address the long-standing challenge of implementing quantum bit commitment protocols experimentally.
• To overcome the primary barrier in existing protocols—requirement for quantum memory—limiting real-world deployment.
• To design a protocol that is secure against all known attacks and compatible with current photonic technology.
• To enable a practical, experimentally feasible implementation of quantum bit commitment using existing hardware.
• To demonstrate that unconditionally secure quantum bit commitment can be realized without quantum memory, enhancing its practical viability.

Proposed method

• The protocol uses a prepare-and-measure approach based on single-photon states prepared in time-bin superpositions.
• It encodes the committed bit using the relative phase between two time bins in a single photon.
• The commitment phase involves preparing a photon in a superposition of early and late time bins, with the phase encoding the bit value.
• The receiver measures the photon in a basis that distinguishes the time-bin superposition, verifying the commitment without storing the quantum state.
• The protocol avoids quantum memory by ensuring all quantum operations are performed in real time during the commitment and verification phases.
• Security is analyzed against general attacks, including those exploiting entanglement or coherent measurements, showing resilience under realistic conditions.

Experimental results

Research questions

• RQ1 Can a quantum bit commitment protocol be designed without requiring quantum memory?
• RQ2 Is it possible to achieve a level of security higher than classical bit commitment using only prepare-and-measure techniques?
• RQ3 Can such a protocol be implemented with current photonic technology and existing single-photon sources and detectors?
• RQ4 How does the protocol's security compare to known limitations of quantum bit commitment, such as Mayers' no-go theorem?
• RQ5 What are the practical constraints and error thresholds that affect the protocol’s feasibility in real-world implementations?

Key findings

• The proposed protocol achieves a security level superior to classical bit commitment, even though unconditional security is generally ruled out by the no-go theorem.
• The protocol does not require quantum memory, making it implementable with current photonic technologies such as single-photon sources and time-bin encoding.
• The protocol is based on a prepare-and-measure scheme using single photons in time-bin superpositions, enabling real-time operation.
• Security analysis shows that the protocol is robust against general attacks, including entanglement-based and coherent measurement strategies.
• The protocol’s feasibility is demonstrated through a detailed analysis of experimental parameters, including photon source stability and detector efficiency.
• The authors conclude that the protocol is a viable path toward experimental realization of quantum bit commitment without the need for quantum storage.