## What is quantum error correction, and why is it important?

Quantum error correction is a set of techniques used to protect the information stored in qubits from errors and decoherence caused by noise.

Quantum computers today have high error rates – around 1 error occurs in 100 operations before failure. For quantum computers to be useful, error rates need to be as low as 1 in a trillion. A huge improvement in performance is needed, however proven progress is already happening in the community.

We are focussed on breaking though this fundamental challenge, by building scalable control systems and fast decoders, and by understanding optimal quantum algorithms for error corrected quantum computers.

"If you don't solve error correction, then you'll never have a useful quantum computer"

- Earl Campbell, Head of Architecture

## Why is quantum error correction such a tough challenge to crack?

Qubits, the building blocks of quantum computers, are extremely sensitive to environmental disturbances. The slightest change in temperature, or any interactions with surrounding molecules could cause a qubit to lose its information. Not only this, but millions of qubits are needed to perform useful calculations.

As such, powerful decoders are required to detect and correct errors with complete accuracy, and at incredible speeds.

### Quantum error correction at scale

## Riverlane Roadmap: Three basic steps to decoder success

Decoding in real-time is a huge challenge for fast quantum computers as a million rounds of measurement results are produced every second. If we don’t decode fast enough, we encounter an exponentially growing backlog of syndrome data. For useful quantum computing, we need to push the scale of the decoder up to so-called Teraquop decoding speeds.

## How are we tackling quantum error correction?

Riverlane team

## The only way to succeed at such a complex problem is through collaboration

Riverlane brings together a multi-disciplinary team of experts in the skills required to understand and manage quantum error correction. We have a team of world class physicists, mathematicians, computer scientists and specialist engineers with decades of combined experience.

### Key papers and projects

#### A real-time, scalable, fast and highly resource efficient decoder for a quantum computer

#### Parallel window decoding enables scalable fault tolerant quantum computation (September 2022)

#### Real-Time Decoding for Fault-Tolerant Quantum Computing: Progress, Challenges and Outlook

#### Belief propagation as a partial decoder

## We're building the operating system for error-corrected quantum computers. This starts with scalable control systems and fast decoders.

### Deltaflow.Control

A customisable software solution to control qubits

### Deltaflow.Decode

The world's first scalable quantum error decoder

## We are proud to partner with world-leading hardware partners and academic labs to deeply understand the quantum stack at all levels, from the qubits up

## Frequently asked questions

### What is the difference between quantum error correction and quantum error mitigation?

Quantum error correction (QEC) and quantum error mitigation (QEM) are two different schemes to deal with noise in devices, which can cause errors in computation.

Quantum error correction methods use multiple physical qubits to represent a single logical qubit. Data is preserved by distributing the information across multiple qubits. Quantum decoders can then detect and correct any errors that occur during computation. Surface code is a popular QEC code.

By contrast, quantum error mitigation methods are employed to infer less noisy outcomes of quantum computations, rather than correcting them. This is often done by repeatedly running slightly different circuits and classically post-processing the results. As an example, zero noise extrapolation is a popular error mitigation method.

QEM methods provide a reduction in noise that can be useful in the NISQ (noisy intermediate-scale quantum) era, as restraints in quantum hardware can make full quantum error correction less feasible. However, for useful computation involving many qubits and deep circuits, full quantum error correction will be necessary.

### What is the difference between error corrected and fault tolerant quantum computers?

Quantum error correction and fault-tolerant quantum computers are often informally used interchangeably. To experts the terms have slightly difference meanings.

Quantum error correction is a scheme for protecting information from noise in device.

Fault-tolerance builds on this. Fault-tolerant quantum computers also prevent errors from spreading during the error correction process or during a computation. It is a richer and broader subject.

To build a useful quantum computer, we really do need fault-tolerance and not just error correction. At Riverlane, we are really solving the fault-tolerance problem, but often just call out “quantum error correction” since this phrase is more commonly known by non-experts.