Source-linked AI summary
Experimental demonstration of graph-state quantum secret sharing
B. A. Bell, D. Markham, D. A. Herrera-Martí, A. Marin, W. J. Wadsworth, J. G. Rarity, M. S. Tame
TL;DR
Graph-state quantum secret sharing uses multipartite entanglement to support access structures beyond those possible with QQ alone. This work experimentally demonstrates graph-state secret sharing using integrated classical and quantum protocols, including a (3, 4) threshold scheme in which any three players can access the secret while no single player obtains information.
Problem
Graph-state based quantum secret sharing offers promising features for sharing secrets among players, including access structures unavailable to QQ alone.
Method
The experiment uses multipartite entangled graph states for classical (CQ) and quantum (QQ) secret sharing, with protocol certification based on the event Cf that the protocol has not aborted.
Results
A (3, 4) threshold scheme was demonstrated: any three players can access the secret, while no single player obtains any information.
Takeaways & Limitations
Integrating CQ and QQ secret sharing enables an access structure known to be impossible with QQ alone.
Takeaways & Limitations
The reported protocol has limitations associated with classical mixing and the non-ideal graph state used in the experiment.
Abstract
from arXiv · showhide
Distributed quantum communication and quantum computing offer many new opportunities for quantum information processing. Here networks based on highly nonlocal quantum resources with complex entanglement structures have been proposed for distributing, sharing and processing quantum information. Graph states in particular have emerged as powerful resources for such tasks using measurement-based techniques. We report an experimental demonstration of graph-state quantum secret sharing, an important primitive for a quantum network. We use an all-optical setup to encode quantum information into photons representing a five-qubit graph state. We are able to reliably encode, distribute and share quantum information between four parties. In our experiment we demonstrate the integration of three distinct secret sharing protocols, which allow for security and protocol parameters not possible with any single protocol alone. Our results show that graph states are a promising approach for sophisticated multi-layered protocols in quantum networks.
Introduction
The paper investigates graph-state quantum secret sharing as a network protocol and experimentally demonstrates sharing classical and quantum secrets with photons. It combines classical and quantum protocols to achieve access structures and security properties unavailable to individual protocols alone.
- Graph-state quantum secret sharing distributes a classical or quantum secret so only authorised sets of parties can access it.
- The experiment demonstrates graph-state-based sharing of classical and quantum secrets using photons in a linear-optics setup.
- A five-qubit graph state shares a classical secret among four parties through quantum channels, including security against a distrusted dealer-to-party channel.
- Three protocols of increasing sophistication allow the same graph state to share a quantum secret through quantum channels.
- Combining classical and quantum protocols enables a quantum-secret access structure impossible with QQ alone and supports security against distrusted channels.
- The work demonstrates graph states' capacity to hybridise cryptographic protocols and support sophisticated quantum-network protocols.
Results
The experiment generated and characterized a five-qubit graph state, then used it to demonstrate classical and quantum secret-sharing protocols among four players. The protocols realize threshold access structures, suppress unauthorized information, and support secure sharing over untrusted channels.
- Resource characterization: A negative graph-state witness expectation confirmed genuine multipartite entanglement involving all qubits.The experimental state fidelity was also evaluated against the ideal graph state using seventeen measurement bases.
- Classical secret sharing: The classical protocol distributes a secret among four players so any three can recover it while any single player obtains no information.Individual players had almost zero accessible information in both the Z and Y bases, with reduced states close to maximally mixed.
- Quantum secret sharing: The graph state implements a (3,1,4) quantum ramp scheme and upgrades it to a (3,4) threshold scheme through hybrid quantum secret sharing.The hybrid construction combines quantum and classical secret sharing to achieve an access structure unavailable to a qubit pure quantum secret-sharing protocol alone.
- Secure quantum secret sharing: The secure quantum secret-sharing protocol verifies transmitted states over untrusted channels and links passing the test to high-fidelity secret retrieval.The experiment introduced SQQ for a (3,4) threshold scheme; the extension to general access structures was deferred to future work.
Discussion
The experiment used a five-qubit graph state in an all-photonic setup to encode, distribute, and retrieve classical and quantum secrets among four players. Integrating classical and quantum secret-sharing protocols enabled access structures and protocol parameters unavailable to individual protocols alone.
- Experimental platform: A five-qubit graph state was generated photonicly for encoding, sharing, and retrieving classical and quantum secrets.The setup used photons to implement the graph-state resource.
- Classical secret sharing: The CQ protocol shared a classical random key through a (3, 1, 4) ramp scheme.Any three of four players could perfectly access the secret, while no single player obtained information.
- Quantum secret sharing: The QQ protocol achieved the same access structure for a quantum secret: any three players could access it, while fewer had no information.This access structure was elevated to a (3, 4) threshold scheme for quantum-secret sharing.
- Integrated protocols: The hybrid QQ protocol combined classical secret sharing with QQ to achieve an access structure impossible with QQ alone.Integrating the protocols expanded the available secret-sharing structures.
- Integrated protocols: A new SQQ protocol was introduced for sharing a quantum secret over untrusted channels.Together with the hybrid QQ protocol, it demonstrated how graph-state tasks can be combined to obtain protocol parameters and security unavailable from any single protocol.
- Implications: The demonstrated flexibility of graph states supports their potential for sophisticated quantum-network protocols.The discussion identifies graph states as a promising technology for future quantum networks.
Methods
The experiment generated a five-qubit graph state with an all-optical, photon-based setup and evaluated its entanglement and secret-sharing access structure. The protocol analysis identifies which player sets can retrieve quantum information and verifies security through measurement-based tests.
- Graph-state generation: Photon pairs from polarization-entangled and heralded sources were fused into a three-photon GHZ state, converted to a linear graph state, and encoded into five photonic qubits.Path and polarization degrees of freedom represented the qubits, with local rotations and phase shifts implemented optically.
- Graph-state generation: The setup implemented removal of path or polarization qubits by incoherently recombining paths or omitting polarization analysis.These operations modeled players who do not participate in the secret-sharing protocol while retaining access to the complementary degree of freedom.
- Resource characterisation: The five-qubit resource was characterized with an entanglement witness and a fidelity decomposition requiring 17 unique measurement bases.The witness was a locally rotated version of one for a five-qubit linear cluster state and accounted for local complementation operations.
- Secret-sharing access structure: The access analysis found that no single player can obtain information, adjacent pairs obtain none, opposite pairs can access information in a specified basis, and any triplet can access the secret.For the quantum-quantum protocol, the dealer teleports a secret state, publicly announces Bell-measurement results, and authorized sets apply corrections and decoding operations.
- Secret-sharing access structure: The protocol’s mixed states give authorized sets full information in some cases and only partial information in others, while passing the certification test implies high output-state fidelity.Players lacking the required classical information cannot access the secret in the corresponding protocol cases.