EPSRC logo

Details of Grant 

EPSRC Reference: EP/Y004620/1
Title: Unlocking the potential of Quantum LDPC Codes for low-overhead fault-tolerance
Principal Investigator: Browne, Professor D
Other Investigators:
Researcher Co-Investigators:
Project Partners:
National Physical Laboratory Riverlane Thales Ltd
Department: Physics and Astronomy
Organisation: UCL
Scheme: Standard Research
Starts: 01 June 2023 Ends: 31 March 2025 Value (£): 382,805
EPSRC Research Topic Classifications:
EPSRC Industrial Sector Classifications:
Aerospace, Defence and Marine Information Technologies
Related Grants:
Panel History:
Panel DatePanel NameOutcome
25 Apr 2023 Software Enabled Quantum Computation Announced
Summary on Grant Application Form
Quantum computers have huge promise to solve problems which lie beyond the capabilities of even the world's fastest conventional computer using quantum effects to compute in a fundamentally new way. However, quantum effects are fragile. Quantum systems are vulnerable to noise and error due to interactions with the world around them, and this noise and error tends to render a quantum computer no more powerful, at best, than a conventional classical computer.

While progress in engineering prototype quantum computers to reduce this error is impressive, and clever algorithmic tricks are being developed to help minimise its effects, to run the most valuable large-scale computations on a quantum computer, the noise needs to be removed almost entirely.

This can be done using the techniques of quantum error correction, where quantum data is stored in an error correcting code. The leading quantum error correcting code is called the surface code - a particularly simple code with a repeated regular structure which can be realised on a two-dimensional surface. The surface code is now very well studied, and the full details of how it can be used to store data, correct errors and implement logical gates are well studied. It is the leading approach to large scale quantum computation and most industrial roadmaps for building such a device are based on it.

However, the surface code has a key disadvantage. It is a highly inefficient way of storing information, and very large numbers of quantum bits (qubits) are required to use it for even a relatively modest computation. For every quantum bit used for computation, thousands or more are needed for the error correction.

There has thus been an ongoing search, over the last 25 years since the surface code was discovered, to find more efficient codes, which nevertheless share some of the practical advantages of the surface code. Potential candidates for such codes have very recently been discovered. They are in a family of codes known as Quantum Low-Density Parity Check codes (or QLPDC codes). Classical LDPC codes are widely used due to their efficient encoding and useful properties, for example in the error correction used in 5G mobile networks. The quantum analogues of these have been studied for nearly 20 years, but only in 2022 was a quantum code discovered which is as efficient in data storage as the best classical codes.

This code, and codes like it, promise to revolutionise the path to large-scale fault tolerant quantum computation, dramatically reducing the number of quantum bits, and therefore hastening the development of large-scale quantum computers.

To realise this promise, however, much work needs to be done. Unlike the simple structure of the surface code, these new highly efficient codes are very complicated. It is therefore far from clear whether their benefits can be realised in practical hardware. Furthermore, little is known about the best way to use such codes for computation. This aim of this project is to fully assess the feasibility of novel QLDPC codes for large-scale quantum computation.

We shall do this by designing detailed models of the measurements which detect errors, and discover new ways to realise quantum gates on these codes. The research will be facilitated by the design of software which will translate the complicated abstract descriptions of the codes into a specification of the building blocks (gates and measurements) which will be realised on the device. We will determine the resources required, in terms of number of qubits and gates, to achieve a set of benchmark computations provided by our project partners, and use these to enable to a fair practical comparison between the resources required to construct a useful quantum computer based on these novel codes compared to the standard surface code.

Key Findings
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
Potential use in non-academic contexts
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
Description This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
Date Materialised
Sectors submitted by the Researcher
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
Project URL:  
Further Information:  
Organisation Website: