Simon Benjamin's

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 from the lower code is fed into a customized, advanced controller for the high-level code so that it makes smarter choices. Numerical simulations confirm the Read more…

In general, metrology aims to increase the precision of measuring a physical quantity, such as time or the strength of a magnetic or electric field. This precision is typically limited by statistical errors and can be enhanced by repeating experiments many times and averaging their results. Quantum metrology takes fundamental limitations on the measurement process into account which are imposed by quantum mechanics and by the fact that measurement devices are described by their quantum Read more…

QTechTheory welcomes its newest member Bálint Koczor, joining as a postdoctoral researcher! Bálint is supported both the EU Flagship project AQTION, visit the website here.

We develop a completely new variational quantum algorithms for simulating general processes, one of which can compute the general matrix multiplication to a vector, while the other is for simulating the general first order derivative equation. These algorithms appear to have a large amount of applications, such as quantum machine learning. Also, as one of applications, we simulated stochastic Lindblad master equation. For more details, please refer to our paper on arXiv. https://arxiv.org/abs/1812.08778

Several of the group’s papers in the last year have focused on the theory behind so-called hybrid quantum algorithms — where a conventional computer and a quantum coprocessor work in tandem. These methods are typically variational because the quantum machine has a number of parameters (essentially, knobs that can be adjusted) and the conventional machine determines how to vary the parameters to find the right settings to solve a given problem. One promising application is Read more…

Working with Alexander Mayorov from Cambridge and Xiao Shan from Oxford Chemistry, we’ve looked into the prospects for modelling molecular vibrations using a quantum computer. Vibrations are are the core of many important phenomena such as spectral properties, energy transfer, and molecular bonding — but they are hard to model and understand using classical (i.e. conventional) computers as a tool. We hope that it will be possible to instead use a quantum computer — even Read more…

Together with Alán Aspuru-Guzik, our group has put together a pretty comprehensive review of quantum computers for chemistry simulation. It’s written with examples and aimed at allowing people from either community to get to grips with this exciting interdisciplinary area. We just updated the arxiv version so it’s a good time to grab it and take a read — let us know what you think!

The hamiltonian simulation is to simulate the dynamics of the system, given some Hamiltonian. The conventional way of the Hamiltonian simulation is the Trotter decomposition. We discretize the simulated time to small time steps, like the classical Runge–Kutta method. Although if we increase the steps of the discretization, we can in principle reduce the algorithmic error, the physical error like dephasing increases linearly to the number of the Trotter steps. Therefore, there are an optimised Read more…