Here you can find some useful links to background reading, a summary of the QCDA project and an outline of the workpackages.

Background reading

For those interested in QCDA but without the background knowledge, we recommend the following lectures notes and review papers:

Prof Dan Browne’s lecture notes on Topological Codes and Quantum Computation

The Steep Road Towards Robust and Universal Quantum Computation
Earl T. Campbell, Barbara M. Terhal, Christophe Vuillot
Nature 549 172 (2017)

Quantum error correction for quantum memories
Barbara M. Terhal
Rev. Mod. Phys. 87, 307 (2015)

Quantum error correction: an introductory guide
Joschka Roffe
Contemporary Physics (2019)

Project Summary

General purpose quantum computers must follow a fault-tolerant design to prevent ubiquitous
decoherence processes from corrupting computations. All approaches to fault-tolerance
demand extra physical hardware to perform a quantum computation. Kitaev’s surface, or toric,
code is a popular idea that has captured the hearts and minds of many hardware developers,
and has given many people hope that fault-tolerant quantum computation is a realistic
prospect. Major industrial hardware developers include Google, IBM, and Intel. They are all
currently working toward a fault-tolerant architecture based on the surface code. Unfortunately,
however, detailed resource analysis points towards substantial hardware requirements using
this approach, possibly millions of qubits for commercial applications. Therefore,
improvements to fault-tolerant designs are a pressing near-future issue. This is particularly
crucial since sufficient time is required for hardware developers to react and adjust course

This consortium will initiate a European co-ordinated approach to designing a new generation
of codes and protocols for fault-tolerant quantum computation. The ultimate goal is the
development of high-performance architectures for quantum computers that offer significant
reductions in hardware requirements; hence accelerating the transition of quantum computing
from academia to industry. Key directions developed to achieve these improvements include:
the economies of scale offered by large blocks of logical qubits in high-rate codes; and the
exploitation of continuous-variable degrees of freedom.

The project further aims to build a European community addressing these architectural issues,
so that a productive feedback cycle between theory and experiment can continue beyond the
lifetime of the project itself. Practical protocols and recipes resulting from this project are
anticipated to become part of the standard arsenal for building scalable quantum information

Scientific Workpackages

WP1: Qubit codes and decoders

WP1.1 Generic LDPC codes and decoders
WP1.2 Topological LDPC codes and decoders
WP1.3 Single-shot error-correction

WP2: Universal logic & compiling

WP2.1 Transversal gates in LDPC codes
WP2.2 Computation by code deformation
WP2.3 Distillation of exotic magic states

WP3: Implementing QEC

WP3.1 Realistic simulations of quantum error correction
WP3.2 Small stabilizer code Implementation
WP3.3 Implementing large LDPC codes
WP3.4 Bosonic or spin code implementation

WP4: Continuous variable architectures

WP4.1 CV error-correcting codes
WP4.2 CV logical gates & resource states
WP4.3 Active noise-suppression for CV systems

Open Problems

A list of open problems was compiled during the QCDA kickoff meeting in Paris in November 2018.