A quantum network for distributed quantum computation

Project Information

QUNET

Grant agreement ID: 852410

DOI

10.3030/852410

Project closed

EC signature date 2 October 2019

Start date 1 November 2019

End date 30 November 2024

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 499 910,00

EU contribution

€ 1 499 910,00

Coordinated by

TECHNISCHE UNIVERSITEIT DELFT
Netherlands

Periodic Reporting for period 4 - QUNET (A quantum network for distributed quantum computation)

Reporting period: 2024-05-01 to 2024-11-30

Summary of the context and overall objectives of the project

A key question for quantum science is: Can quantum systems be protected from decoherence? This is not just a fundamental question; if we can reliably control large quantum states, it becomes possible to perform certain important computational and information tasks that go beyond classical physics.

A promising approach is to protect quantum states by distributing quantum error correction over quantum networks. These networks consist of nodes that contain quantum bits to store and process quantum states, and that are connected by entanglement links based on photons. This approach is naturally scalable to larger sizes by connecting independent modules.

The goal of this project is to realize a proof-of-principle demonstration for such an error-corrected distributed quantum system. Our qubits are based on an atomic defect in diamond, the nitrogen-vacancy center. We use the electron spin of this defect to control multiple nuclear spin qubits in its vicinity. These spin qubits in diamond combine high operation temperatures, good quantum coherence and the ability to optically link them together into a quantum network. The final goal of this project is to realize a system consisting of multiple nodes, and demonstrate a quantum error detection distributed over that small-scale network. This network functions as a unit cell for large-scale quantum computation.

Reaching this goal will be a potentially decisive step towards large quantum networks and distributed quantum computations: we will approach a new territory in which quantum states can be made more stable by making networks larger and larger, ultimately completely overcoming decoherence.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The main results from this project are:

(1) The precise 3D imaging and characterization of large (50+) coupled spin systems in diamond [Nature Commun. 15:2006, 2024]

(2) The operation of a logical qubit of a fault tolerant error correction code [Nature 606, 884, 2022]

(3) The realization of a many-body-localized discrete time crystal [Science 374,1474, 2021]

(4) Robust quantum-network memory based on spin qubits in isotopically engineered diamond [NPJ Quantum Information 8, 122, 2022]

(5) Extremely long-lived spin-pair qubits with coherence times exceeding minutes [Phys. Rev. X 12, 011048, 2022, arXiv:2311.10110]

(6) High-fidelity universal gates for spin qubits in diamond [arXiv:2403.10633​]

(7) A theoretical study of thresholds for the distributed surface code [AVS Quantum Sci. 6, 033801, 2024]

(8) A generalized understanding of two-qubit quantum gates for spin qubits in diamond [arXiv:2409.13610 and arXiv:2409.08977]

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

This project has significantly improved our understanding and control of spin qubits in diamond for quantum networks and distributed quantum computation and simulation.

Illustration of entanglement and error correction using spin qubits in diamond