Connecting Qubits with a Topological Waveguide

Janet Zhong

Waveguide quantum electrodynamic (waveguide QED) systems (arrays of qubits coupled to a waveguide) can exhibit a vast array of phenomena from collective effects, non-trivial topology to novel localisation effects. This thesis is the first study of a long-range coupled topological waveguide QED system. The existence of topological edge states for when one photon is incident on a spatially modulated qubit array is numerically verified and the results are analogous to a photonic crystal set-up in Ref. [1]. This thesis then goes beyond the single photon regime to consider the effect of interactions for when two photons are incident in the qubit array. Bound photon pairs and bound pair edge states are readily observed. Numerical results suggest that the bound pair edge states are topologically non-trivial, however, a topological invariant should be calculated before making stronger conclusive statements. Even more interestingly, the two-photon qubit array can also exhibit a self-induced localised state. This appears to be a completely unexplored effect that can connect many body physics, collective effects as well as topological properties. The exotic topological properties of these waveguide QED systems are promising developments in the growing field of quantum topological photonics which is said to have large potential for quantum computing technologies. The novel localised states also reveals that the physics of waveguide QED systems are richer than expected with many unexplored phenomena.

S. Das Sarma

Anonymous

Eunjong Kim, Xueyue Zhang, Vinicius S. Ferreira +7 more

While designing the energy-momentum relation of photons is key to many linear, nonlinear, and quantum optical phenomena, a new set of light-matter properties may be realized by employing the topology of the photonic bath itself.In this work we experimentally investigate the properties of superconducting qubits coupled to a metamaterial waveguide based on a photonic analog of the Su-Schrieffer-Heeger model.We explore topologically induced properties of qubits coupled to such a waveguide, ranging from the formation of directional qubit-photon bound states to topology-dependent cooperative radiation effects.Addition of qubits to this waveguide system also enables direct quantum control over topological edge states that form in finite waveguide systems, useful for instance in constructing a topologically protected quantum communication channel.More broadly, our work demonstrates the opportunity that topological waveguide-QED systems offer in the synthesis and study of many-body states with exotic long-range quantum correlations.

Garry Goldstein, Liang Jiang, Mikhail D. Lukin

Fatih Dinç, Lauren E. Hayward Sierens, Agata M. Brańczyk

We study the collective decay rates of multidimensional quantum networks in which one-dimensional waveguides form an intersecting hyperrectangular lattice, with qubits located at the lattice points.We introduce and motivate the dimensional reduction of poles (DRoP) conjecture, which identifies all collective decay rates of such networks via a connection to waveguides with a one-dimensional topology (e.g., a linear chain of qubits).Using DRoP, we consider many-body effects such as superradiance, subradiance, and bound states in continuum in multidimensional quantum networks.We find that, unlike one-dimensional linear chains, multidimensional quantum networks have superradiance in distinct levels, which we call multidimensional superradiance.Furthermore, we generalize the N -3 scaling of subradiance in a linear chain to d-dimensional networks.