Metamaterials in Superconducting and Cryogenic Quantum Technologies

  1. Alex Krasnok
The development of fault-tolerant quantum computers based on superconducting circuits faces critical challenges in qubit coherence, connectivity, and scalability. This review establishes
metamaterials, artificial structures with on-demand electromagnetic properties, as a transformative solution. By engineering the photonic density of states, metamaterials can suppress decoherence via the Purcell effect and create multi-mode quantum buses for hardware-efficient control and long-range qubit coupling. We provide a comprehensive overview, from foundational principles and Hamiltonian engineering to the materials science of high-coherence devices. We survey state-of-the-art performance, highlighting record coherence times and coupling strengths achieved through metamaterial design. Furthermore, we explore advanced applications where engineered environments give rise to exotic excitations and topologically protected states, enabling novel error correction schemes and qubit architectures. Ultimately, we argue that metamaterials are evolving from passive components into the core architectural element of next-generation quantum technologies, paving a viable path toward scalable quantum computation.

Advancements in Superconducting Microwave Cavities and Qubits for Quantum Information Systems

  1. Alex Krasnok,
  2. Pashupati Dhakal,
  3. Arkady Fedorov,
  4. Pedro Frigola,
  5. Michael Kelly,
  6. and Sergey Kutsaev
Superconducting microwave cavities with ultra-high Q-factors are revolutionizing the field of quantum computing, offering long coherence times exceeding 1 ms, which is critical for
realizing scalable multi-qubit quantum systems with low error rates. In this work, we provide an in-depth analysis of recent advances in ultra-high Q-factor cavities, integration of Josephson junction-based qubits, and bosonic-encoded qubits in 3D cavities. We examine the sources of quantum state dephasing caused by damping and noise mechanisms in cavities and qubits, highlighting the critical challenges that need to be addressed to achieve even higher coherence times. We critically survey the latest progress made in implementing single 3D qubits using superconducting materials, normal metals, and multi-qubit and multi-state quantum systems. Our work sheds light on the promising future of this research area, including novel materials for cavities and qubits, modes with nontrivial topological properties, error correction techniques for bosonic qubits, and new light-matter interaction effects.