Redundantly Encoded Resource States Achieve Deterministic Photonic Quantum Computing with Boosted Fusion Success Beyond 50%

The creation of complex entangled states remains a central challenge in the development of photonic quantum computers and quantum communication networks. Samuel J. Sheldon from Aegiq Ltd. and Pieter Kok from the University of Sheffield demonstrate a new method for generating these crucial resource states with significantly improved efficiency. Their work addresses the inherent probabilistic nature of fusing smaller entangled states, a process that typically yields only a 50% success rate. By redundantly encoding the building blocks of these states using Greenberger-Horne-Zeilinger states, the researchers achieve a protocol for deterministic generation, paving the way for more reliable and scalable quantum technologies and offering a route to efficiently construct complex entangled qubit states for advanced quantum applications.

Photonic Graph States with Built-in Redundancy

Researchers are developing methods to generate robust resource states for photonic quantum computing, essential for building powerful quantum computers. This work investigates creating resource states with built-in redundancy, designed to overcome imperfections in photonic systems. The approach encodes logical qubits within highly entangled states, utilising graph states with a specific structure that allows for the detection and correction of errors caused by photon loss, a significant challenge in these systems. The research demonstrates the feasibility of generating these states with high entanglement and fidelity, paving the way for more reliable and scalable photonic quantum computation. Furthermore, the team explores the trade-offs between redundancy levels, state preparation complexity, and achievable error thresholds, providing valuable insights for designing practical quantum algorithms and architectures.

Many strategies for constructing large photonic cluster states rely on fusing smaller resource states generated by quantum emitters. This fusion process is often probabilistic, typically succeeding only 50% of the time. A recent proposal suggests that, with low photon loss, the probability of successful fusion can be dramatically increased by redundantly encoding vertices of linear graph states using Greenberger-Horne-Zeilinger states. The team presents a protocol for deterministically generating these redundantly encoded photonic resource states using single quantum emitters, offering a significant advancement in the field.

Photonic Errors in GHZ State Encoding

This research provides a detailed analysis of error mechanisms affecting photonic quantum computing and communication schemes. It examines potential sources of error when creating and manipulating entangled photons for building quantum computers or secure communication networks. The system relies on encoding logical qubits across multiple photons using GHZ states to provide resilience against errors, with photonic fusion combining entangled states from different parts of the network. Information is encoded in the arrival time of photons, a common technique in photonic quantum information processing. The research focuses on understanding how these errors modify the resource state and affect the vertices, the building blocks of the larger entangled network.

The analysis reveals several potential error sources, including spin-flip errors caused by imperfect control over quantum emitter excitation, inefficient excitation where emitters fail to produce photons, and off-resonant excitation introducing additional photons. However, photon loss is the most significant error, completely destroying entanglement within redundantly encoded vertices and preventing fusion. While redundancy provides some resilience against errors, minimising photon loss is critical for the success of this scheme.

This research provides a detailed characterisation of error mechanisms in photonic quantum systems, highlights the importance of redundant encoding for error mitigation, and outlines the system requirements for achieving robust entanglement. Scaling up this system will require overcoming these error mechanisms and provides a foundation for developing error correction techniques.

Deterministic Photonic Qubit Encoding with Quantum Dots

Researchers have demonstrated a protocol for deterministically generating redundantly encoded photonic resource states using single quantum emitters, paving the way for more efficient construction of complex entangled qubit states crucial for quantum technologies and quantum repeaters. The team successfully outlined a method leveraging the properties of quantum dot systems, specifically single cavity-coupled charged quantum dots and charged quantum dot molecules, to create these resource states. By utilising cyclical transitions for photon generation and carefully controlling ground state populations, the researchers encoded qubits in the time-bin basis, ensuring the system returns to its initial state after excitation and avoiding unwanted spin flips. The work addresses a key challenge in measurement-based quantum computing, which relies on large entangled cluster states.

The team’s approach boosts the probability of successful fusion of smaller resource states, a process typically limited by a 50% success rate. By redundantly encoding vertices using Greenberger-Horne-Zeilinger states, the protocol aims to achieve near-unity fusion probability, significantly enhancing the efficiency of building these complex entangled states. Future work will likely focus on optimising the protocol for different quantum dot systems and mitigating the impact of errors to further improve the fidelity and scalability of entangled state generation.