A quantum error-correcting code is a central piece of fault-tolerant quantum computation that is required to realise large-scale quantum algorithms. Unfortunately, the state-of-the-art codes with the best parameters that require the least overheads do not yet admit experimentally feasible implementations. Therefore, exploring codes that are both high-performing and practical on Read more…
The most promising class of algorithms for near-term quantum computers are variational quantum algorithms (VQAs), where a parametrised circuit of quantum gates calculates some cost function, which is then optimised to produce the solution to a problem, e.g. calculating the ground-state energy of a molecule. Typically, the optimisation methods used Read more…
A promising approach to build a scalable quantum computer is to manufacture a large array of qubits on a chip. This is common to several hardware architectures including superconducting qubits and spin-qubits in silicon. The qubits are engineered to perform logical quantum operations and detect local errors at the same Read more…
Present and near-term quantum computers could help us to solve important practical problems by preparing increasingly complex quantum states that cannot be simulated classically with realistic levels of resource. However, imperfections in their quantum operations (noise) severely limits their practical applicability. Two recent works [arXiv:2011.05942, arXiv:2011.07064] have introduced an approach that now Read more…
QuESTlink is a wonderful and extremely useful tool when it comes to testing, understanding or developing quantum algorithms. It is a Mathematica interface that lets its users to take full advantage of the highly efficient QuEST code without resorting to writing low-level C code: see our blogpost here. We have Read more…
Quantum algorithms have introduced a new paradigm in computing, but they typically estimate expectation values by sampling output probabilities of a quantum computer. In order to reduce the uncertainty of such an expectation value, one needs to repeat measurements in a quantum algorithm many times. We consider the measurement cost Read more…
Gradient descent is well-known and widely used in many scientific applications. In many scenarios the aim is to find the minimum of a function; gradient descent does this by always moving in the direction of the steepest descent. This is analogous to how a person would find the way from Read more…
We have a tutorial-style preprint explaining all about QuESTlink — a tool allowing Mathematica users to take full advantage of the power of the QuEST system without writing a single line of c code. QuEST itself is one of the world’s highest-performing and most flexible quantum simulation systems, used by Read more…
Our review of quantum computation chemistry has now been published online at Reviews of Modern Physics. The journal link is here, but if you can’t access the journal then the preprint is freely available here.
Practical large-scale quantum computers require active error correction, but for this to work, the components must reach fidelities that are very challenging. In this theory paper, we customise the leading ‘surface code’ approach, layering it on top of a second simpler code to detect the most common noise type. Information Read more…