PhD Studentship: Terahertz Photons for Quantum Control and Topological Quantum Information

Principal supervisor name: Arijeet Pal Principal supervisor UCL profile website: https://profiles.ucl.ac.uk/66876-arijeet-pal Funding: Maintenance stipend at UELA enhanced rate - rises each year (For 2026/27, the total stipend is expected to be £26,022, i.e. £1,500 above the UKRI London-weighted rate of £24,522) Project summary Terahertz (THz) frequencies occupy a largely unexplored regime for quantum technologies, bridging conventional microwave quantum circuits and optical platforms. The energy of a THz photon naturally matches important excitations in quantum materials, including cyclotron transitions, collective modes and Landau-level excitations. This PhD project will investigate how quantum states of THz radiation can be used to manipulate matter at the single- and few-photon level and, ultimately, to engineer robust qubits based on topological quantum states. A central direction will be the strong and ultrastrong coupling of confined THz photons to two-dimensional electron systems in high magnetic fields. In the quantum Hall regime, coupling cyclotron and collective electronic excitations to THz cavity modes produces hybrid light–matter states known as Landau polaritons. The project will develop theoretical models for controlling these states using shaped THz pulses, cavity engineering and nonlinear interactions. We will investigate whether individual polaritonic excitations can constitute effective two-level systems and determine how their coherence, interactions and readout could be optimised. A more ambitious objective is to explore whether THz cavities can manipulate or mediate interactions between topological excitations in integer and fractional quantum Hall states. In particular, the project will investigate cavity induced interactions, photon-mediated coupling between spatially separated edge or bulk excitations, and protocols for creating and controlling entangled states. An important question will be whether coupling to THz photons can provide new routes towards protected quantum information processing, including manipulation of fractionalised excitations and candidate topological qubits. The research will combine quantum optics, condensed-matter theory and numerical modelling of driven open quantum systems, with close connections to experimentally achievable THz cavities and quantum materials. It will establish the opportunities †and fundamental limits- of THz photons as a new resource for quantum control and topological quantum technologies.