[Paper Review] Quantum Blockchain using entanglement in time

Del Rajan, Matt Visser|RePEc: Research Papers in Economics|Apr 16, 2018

Quantum Computing Algorithms and Architecture4 citations

TL;DR

This paper proposes a quantum blockchain that encodes data into a temporal Greenberger-Horne-Zeilinger (GHZ) state of photons that do not coexist in time, leveraging entanglement in time to provide a quantum advantage over classical blockchains. The key contribution is that temporal entanglement—rather than spatial entanglement—enables nonclassical influence on the past, offering intrinsic security and a novel mechanism for tamper-proof record-keeping.

ABSTRACT

We propose a conceptual design for a quantum blockchain. Our method involves encoding the blockchain into a temporal GHZ (Greenberger-Horne-Zeilinger) state of photons that do not simultaneously coexist. It is shown that the entanglement in time, as opposed to an entanglement in space, provides the crucial quantum advantage. All the subcomponents of this system have already been shown to be experimentally realized. Furthermore, our encoding procedure can be interpreted as nonclassically influencing the past.

Motivation & Objective

• To design a fully quantum blockchain that integrates naturally into a quantum network, avoiding reliance on classical cryptography.
• To address the threat of quantum computers breaking classical blockchain security by creating a quantum-native solution.
• To explore whether entanglement in time—rather than space—provides a fundamental quantum advantage in blockchain design.
• To demonstrate that all components of the proposed system are experimentally realizable with current technology.
• To investigate the conceptual implications of the system as a form of quantum networked time machine.

Proposed method

• Encoding blockchain data into a temporal GHZ state of photons that are prepared and measured at different times, without simultaneous coexistence.
• Utilizing nonlocal quantum correlations between temporally separated photons to ensure data integrity and immutability.
• Leveraging the fact that measurement outcomes on later photons can retroactively influence the physical description of earlier, already-measured photons.
• Designing the blockchain such that each block is linked via quantum entanglement in time, analogous to cryptographic hashing in classical blockchains.
• Ensuring that any tampering with a past block would disrupt the entanglement structure, thereby invalidating the entire chain.
• Integrating the system into a quantum network framework to enable distributed consensus and secure communication.

Experimental results

Research questions

• RQ1 Can a blockchain be constructed entirely from quantum information using entanglement in time rather than spatial entanglement?
• RQ2 Does entanglement in time provide a superior quantum advantage over classical or spatially entangled blockchains?
• RQ3 Can the encoding process be interpreted as nonclassical influence on the past, and what are the implications for causality and information flow?
• RQ4 Are all components of such a system experimentally realizable with current photonic technology?
• RQ5 Can this system be viewed as a quantum networked time machine, and what experimental probes does it enable?

Key findings

• The proposed quantum blockchain uses temporal GHZ entanglement between non-coexisting photons to encode data, ensuring tamper resistance through quantum nonlocality.
• Entanglement in time, not space, is shown to be the crucial resource for the quantum advantage, as it enables nonclassical influence on past events.
• The system can be interpreted as a form of quantum networked time machine, where current measurements affect the physical description of past events.
• All required components—preparation, measurement, and entanglement in time—have been experimentally demonstrated in photonic systems.
• The design is compatible with existing quantum networks and could be implemented using current photonic technology, including space-based quantum links.
• The framework opens new avenues for probing quantum causality, time travel paradoxes, and the foundational nature of time in quantum information.