Quantum information and quantum computing

Quantum reservoir computing is a promising paradigm in quantum machine learning that harnesses the inherent properties of quantum systems to enhance information processing. This research explores the potential of quantum-inspired approaches, leveraging the rich dynamics of quantum reservoirs to solve complex computational tasks with improved efficiency and accuracy.

We are exploring the use of two-level atomic systems coupled to Lorentzian photonic cavities as a quantum computing reservoir system and are deploying its study both to standard machine-learning image-recognition problems and to the dynamics of open quantum systems. Our results suggest that the quantum physical reservoir computer is equally effective in generating valuable representations for quantum problems, even when faced with limited training data. We also apply QRC to real world problems and collaborate with industry on implementing the method on solid-state devices. 

The race to scale up quantum processors is increasingly limited not only by decoherence, but by how accurately large numbers of qubits can be driven and calibrated in realistic devices. At Surrey, we develop scalable optimal-control methods that reduce gate errors while remaining practical for larger processor architectures, including approaches tailored to fixed-coupling qubit arrays and imperfect device characterisation. Recent work shows how control problems on 2D qubit arrays can be decomposed into efficiently optimised commuting blocks, enabling high-fidelity universal gates with built-in robustness to parameter uncertainty. We also study robust pulse design for superconducting transmon qubits under systematic control errors, combining theory and experiment to demonstrate resilience to calibration drift and hardware imperfections. Our research in this area is balanced between applications to different architectures including experimental testing, and between developing computational and theoretical methods.

Topological superconductors and related engineered quantum circuits offer routes to encoding information in states that are intrinsically less sensitive to local noise and disorder. Our research develops theoretical models and control strategies for topological and symmetry-protected quantum hardware. Our work has explored microwave-circuit methods for measuring and controlling fermion-parity states in Majorana devices, as well as spectroscopic signatures that help distinguish topological Majorana modes from conventional Andreev bound states. In parallel, we investigate protected-state engineering in Josephson-junction chains, where Hamiltonian symmetries can enhance coherence and suppress relaxation and dephasing — an approach that is relevant for robust quantum memory and precision quantum sensing.

The study of superfluid ³He has important particle-physics and cosmological implications. The normal phase of pure liquid ³He is separately invariant under spin and orbital rotations, gauge transformations, as well as discrete symmetries of space and time inversion. This rich symmetry structure has a close correspondence to the complex symmetry of the early universe.

It is believed that the early universe evolved after the Big Bang through a series of symmetry-breaking phase transitions, analogous to those in superfluid ³He. The Standard Model is an effective theory describing the low-energy phenomena that emerge from the cosmological vacuum.

In an analogous way, the effective theory describing the collective modes, quasiparticles and defects that emerge from the ground state of superfluid ³He offers a laboratory analogue of Standard-Model physics, due to the similarity of the maximal symmetry group with that of the early universe.

We propose superfluid ³He as a quantum simulator for Standard-Model physics in the laboratory. The low-pressure, low-temperature B-phase of this quantum liquid is a paradigm for time-reversal-invariant topological order. When ³He-B is confined on the mesoscopic scale (comparable to its coherence length), Andreev bound states with a Dirac-type spectrum are confined to the boundary of the superfluid. These are spin-polarised Majorana fermions created by Andreev processes at the boundary. Probing these states can shed light on hidden spinor degrees of freedom, testing the superselection rule in the Standard Model.

We have designed a device to probe this physics — a hybrid superconducting-superfluid device that could serve as an analogue of the superconducting quantum circuit. We aim to investigate the fundamental physics of qubit operation in this analogue system.