Novel error-correction scheme developed for quantum computers
Dr Arne Grimsmo from Sydney Nano and the School of Physics. Photo: Stefanie Zingsheim
Scientists in Australia have developed a new approach to reducing the errors that plague experimental quantum computers; a step that could remove a critical roadblock preventing them scaling up to full working machines.
By taking advantage of the infinite geometric space of a particular quantum system made up of bosons, the researchers, led by from the University of Sydney, have developed quantum error correction codes that should reduce the number of physical quantum switches, or qubits, required to scale up these machines to a useful size.
âThe beauty of these codes is they are âplatform agnosticâ and can be developed to work with a wide range of quantum hardware systems,â Dr Grimsmo said.
âMany different types of bosonic error correction codes have been demonstrated experimentally, such as and ,â he said. âWhat we have done in our paper is unify these and other codes into a common framework.â
The research, published this week in , was jointly written with from the University of Queensland and from RMIT University. The collaboration is across two leading quantum research centres in Australia, the and the .
Robust qubits
âOur hope is that the robustness offered by âspacing things outâ in an infinite Hilbert space gives you a qubit that is very robust, because it can tolerate common errors like photon loss,â said Dr Grimsmo from the and .
Scientists in universities and at tech companies across the planet are working towards building a universal, fault-tolerant quantum computer. The great promise of these devices is that they could be used to solve problems beyond the reach of classical supercomputers in fields as varied as materials science, drug discovery and security and cryptography.
With Google last year that has achieved âquantum supremacyâ â performing an arguably useless task but beyond the scope of a classical computer â interest in the field of quantum computing and engineering continues to rise.
But to build a quantum machine that can do anything useful will require thousands, if not millions of quantum bits operating without being overwhelmed with errors.
And qubits are, by their very nature, error prone. The âquantumnessâ that allows them to perform a completely different type of computing operation means they are highly fragile and susceptible to electromagnetic and other interference.
Identifying, removing and reducing errors in quantum computation is one of the central tasks facing physicists working in this field.
Fragile superpositions
Quantum computers perform their tasks by encoding information utilising quantum superposition â a fundamental facet of nature where a final outcome of a physical system is unresolved until it is measured. Until that point, the information exists in a state of multiple possible outcomes.
Dr Grimsmo said: âOne of the most fundamental challenges for realising quantum computers is the fragile nature of quantum superpositions. Fortunately, it is possible to overcome this issue using quantum error correction.â
This is done by encoding information redundantly, allowing the correction of errors as they happen during a quantum computation. The standard approach to achieve this is to use a large number of distinguishable particles as information carriers. Common examples are arrays of electrons, trapped ions or quantum electrical circuits.
However, this creates a large network of âphysical qubitsâ in order to operate a single, logical qubit that does the processing work you require.
This need to create a large network of physical qubits to support the work of a single operating qubit is a non-trivial barrier towards constructing large-scale quantum machines.
Indistinguishable bosons
Dr Grimsmo said: âIn this work, we consider an alternative approach based on encoding quantum information in collections of bosons.â The most common type of boson is the photon, a packet of electromagnetic energy and massless âlight particleâ.
By trapping bosons in a particular microwave or optical cavity, they become indistinguishable from one another, unlike, say, an array of trapped ions, which are identifiable by their location.
âThe advantage of this approach is that large numbers of bosons can be trapped in a single quantum system such as photons trapped in a high-quality optical or microwave cavity,â Dr Grimsmo said. âThis could drastically reduce the number of physical systems required to build a quantum computer.â
The researchers hope their foundational work will help build a roadmap towards fault tolerance in quantum computing.