Polarization Transmon Arrays Demonstrate Nontrivial Topological Phases and In-Gap States

The pursuit of simulating complex quantum systems drives innovation in materials science and condensed matter physics, and researchers are now exploring novel platforms to unlock previously inaccessible phenomena. Ekaterina Konopleva, Gleb Fedorov, and Oleg Astafiev, from the Center for Engineering Physics, Moscow, and the Moscow Center for Advanced Studies, present a superconducting simulator designed to investigate an extension of the “Zig-Zag” model, a key concept in topological physics. Their work utilizes specially designed superconducting circuits called polarization transmons, which exhibit unique quantum properties, to create a system with long-range interactions. The team demonstrates the existence of localized quantum states within this system, paving the way for experimental investigation of complex many-body phenomena and offering a new avenue for exploring the fundamental principles of topological quantum matter.

Zig-Zag Transmon Arrays for Quantum Simulation

Recent years have seen extensive study of quantum simulators designed to model topological systems. This work introduces a promising new approach, utilising meta-atoms with multiple internal properties to provide enhanced control and flexibility in designing complex quantum systems. The team investigates the emergence of nontrivial topological phases in “Zig-Zag” arrays of polarization transmons, superconducting qubits strongly coupled to electromagnetic radiation. These arrays effectively mimic the behaviour of topological insulators, materials characterised by conducting surface states and insulating bulk properties. The researchers demonstrate that edge states, protected from scattering, appear at the boundaries of the “Zig-Zag” array under specific conditions, potentially enabling fault-tolerant quantum computation.

This simulator investigates an extension of the well-known “Zig-Zag” model, incorporating long-range cross-polarization couplings and utilising polarization transmons, which possess degenerate dipole orientations. These transmons are carefully engineered to exhibit strong interactions mediated by the long-range couplings, allowing exploration of complex quantum phenomena. The experimental setup precisely controls the polarization of individual transmons, enabling observation and characterisation of the resulting quantum states and dynamics.

Topological States with Superconducting Artificial Atoms

This research presents a comprehensive investigation into topological quantum simulation using engineered superconducting circuits. The core focus is creating and manipulating topological states of matter using superconducting artificial atoms, a promising approach for fault-tolerant quantum computation due to the inherent robustness of these states. The team constructs zigzag chains of these artificial atoms, structures known to support topological edge states, and extends this work to explore higher-order topological states. The research utilises Josephson junctions, crucial elements in the superconducting circuits providing the nonlinearity needed for quantum behaviour, and relies on tunable parameters to control the properties of the artificial atoms.

Long-range interactions between the artificial atoms are explicitly considered, significantly altering the topological properties of the system. The study also investigates the effects of disorder on the topological states, aiming to enhance their robustness. The researchers have developed a new type of artificial Josephson atom specifically tailored for topological simulation, and are exploring higher-order topological states, with the ultimate goal of leveraging these states for building fault-tolerant quantum computers.

Polarization Transmons Emulate Zig-Zag Model Physics

This research introduces a novel superconducting simulator designed to explore an extended version of the “Zig-Zag” model, a concept within topological physics. The team successfully mapped the model both numerically and analytically, demonstrating the existence of localized states within the energy gap and edge states at the system’s boundaries. Crucially, they demonstrated that a chain of superconducting atoms, termed polarization transmons, accurately emulates the behaviour predicted by the extended “Zig-Zag” model, confirmed by comparing theoretical wavefunctions with electromagnetic modelling, establishing a viable platform for investigating previously inaccessible quantum phenomena.

The researchers observed that longer-range interactions between the superconducting atoms play a key role in coupling different polarization subspaces. They also distinguished between defect states and those arising from the system’s topology, confirming the robustness of the topological states to disorder. Future work will likely focus on extending the chain length and enhancing the coupling between atoms to fully explore the predicted behaviour and investigate higher-order topological materials, paving the way for experimental verification of these complex quantum effects.