arXiv:2006.12794 · Physical review. B./Physical review. B
Topological excitations and bound photon pairs in a superconducting quantum metamaterial
Ilya S. Besedin, Maxim A. Gorlach, Nikolay N. Abramov, Ivan Tsitsilin, Ilya N. Moskalenko, Alina A. Dobronosova, Dmitry O. Moskalev, Aleksei R. Matanin, Nikita S. Smirnov, Ilya A. Rodionov, Alexander N. Poddubny, Alexey Vladimirovich Ustinov
Topological photonics enables resilient routing and localization of light. Of special interest are topological states of quantum light promising disorder-robust quantum correlations. Here, the authors design and fabricate a one-dimensional dimerized array of superconducting qubits. Performing microwave spectroscopy of this fabricated quantum metamaterial, they observe not only single-photon topological states but also the bands of exotic bound photon pairs mediated by the anharmonicity of qubits. They also discuss the two-photon bound edge-localized state and analyze the robustness of photon-photon correlations.
Topological photonics enables resilient routing and localization of light. Of special interest are topological states of quantum light promising disorder-robust quantum correlations. Here, the authors design and fabricate a one-dimensional dimerized array of superconducting qubits. Performing microwave spectroscopy of this fabricated quantum metamaterial, they observe not only single-photon topological states but also the bands of exotic bound photon pairs mediated by the anharmonicity of qubits. They also discuss the two-photon bound edge-localized state and analyze the robustness of photon-photon correlations.
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.
We study quantum features of electromagnetic radiation propagating in a one-dimensional superconducting quantum metamaterial composed of an infinite chain of charge qubits placed within two stripe massive superconducting resonators. The quantum-mechanical model is derived assuming weak fields and that, at low temperatures, each qubit is either unoccupied or occupied by a single Cooper pair. We demonstrate the emergence of two bands of single-photon qubit bound states with the energies lying outside the photon continuum---one is above and the second slightly below the linear photon band. The higher energy band varies slowly with the qubit-photon center of mass quasimomentum. It becomes practically flat provided that the electromagnetic energy is far below the Josephson energy when the latter is small compared to the charging energy. The dispersion of the lower band is practically identical to that of free photons. The emergence of bound states may cause radiation trapping indicating possible applicability for the control of photon transport in superconducting qubit-based artificial media.
Qubits strongly coupled to a photonic crystal give rise to qubit-photon dressed bound states.These bound states, comprising the qubits and spatially localized photonic modes induced around the qubits, are the basis for many exotic physical scenarios.The localization of these states changes with qubit detuning from the photonic crystal band edge, offering an avenue of in situ control of bound-state interaction.Here, we present experimental results from a device with two transmon qubits coupled to a superconducting microwave photonic crystal and realize tunable on-site and interbound state interactions.We observe a fourth-order two-photon virtual process between bound states indicating strong coupling between the photonic crystal and transmon qubits.Because of their localization-dependent interaction, these states offer the ability to realize one-dimensional chains of bound states with tunable and potentially long-range interactions that preserve the qubits' spatial organization.The widely tunable, strong, and robust interactions demonstrated with this system are promising benchmarks towards realizing larger, more complex systems that use bound states to build and study quantum spin models.
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.
Abstract Embedding tunable quantum emitters in a photonic bandgap structure enables control of dissipative and dispersive interactions between emitters and their photonic bath. Operation in the transmission band, outside the gap, allows for studying waveguide quantum electrodynamics in the slow-light regime. Alternatively, tuning the emitter into the bandgap results in finite-range emitter–emitter interactions via bound photonic states. Here, we couple a transmon qubit to a superconducting metamaterial with a deep sub-wavelength lattice constant (λ/60). The metamaterial is formed by periodically loading a transmission line with compact, low-loss, low-disorder lumped-element microwave resonators. Tuning the qubit frequency in the vicinity of a band-edge with a group index of ng = 450, we observe an anomalous Lamb shift of −28 MHz accompanied by a 24-fold enhancement in the qubit lifetime. In addition, we demonstrate selective enhancement and inhibition of spontaneous emission of different transmon transitions, which provide simultaneous access to short-lived radiatively damped and long-lived metastable qubit states.
Quantum technologies, holding the promise of exponentially superior performance in comparison to their classical counterparts for certain tasks, have consistently encountered challenges, including instability in quantum light sources, quantum decoherence, and vulnerability to losses that topological photonics happens to adeptly address. Here, we theoretically put forth a quantum Su-Schrieffer-Heeger-type chain designed to greatly enhance single-photon blockade (single PB) effect with topological protection. By designing the deliberate coupling strengths, the quantum level lattices take the form of a one-dimensional array with a topological edge state in single-excitation space and a two-dimensional square breathing lattice with topological corner states in two-excitation space, resulting in enhanced single-photon excitation and the suppression of two-photon transitions. Therefore, the second-order correlation function is diminished by up to 2 orders of magnitude at the cavity resonance frequency, accompanied by stronger brightness. Furthermore, the PB effect is robust to local perturbations in cavity-qubit coupling and qubit frequency, benefitting from topological protection.