Gioele Consani

3D Integrated Embedded Filters for Superconducting Quantum Circuits

  1. Waqas Ahmad,
  2. Gioele Consani,
  3. Mohammad Tasnimul Haque,
  4. Jacob Dunstan,
  5. and Brian Vlastakis
Microwave filtering for superconducting qubits is a key element of quantum computing technology, enabling high coherence and fast state detection. This work presents the design and
implementation of novel microwave Purcell filters for superconducting quantum circuits, integrated within a multilayer printed circuit board (PCB). The off-chip design removes all filter components from the qubit substrate, reducing device complexity, improving layout footprint and allowing better scalability to large qubit counts. Each embedded filter can couple up to nine readout resonators, enabling efficient multiplexed readout. Electromagnetic simulations of the filter predict a thousand-fold improvement in qubit isolation from the readout port. The design was experimentally validated under cryogenic conditions in conjunction with a 35-qubit device, demonstrating compatibility of the PCB-based filter with high-coherence superconducting qubits. The comparison of the measured qubit median T1 of 84 μs with the expected radiative limit from electromagnetic simulations validated the presence of Purcell filtering in the system.
arxiv pdf

Effective Hamiltonians for interacting superconducting qubits — local basis reduction and the Schrieffer-Wolff transformation

  1. Gioele Consani,
  2. and Paul A. Warburton
An open question in designing superconducting quantum circuits is how best to reduce the full circuit Hamiltonian which describes their dynamics to an effective two-level qubit Hamiltonian
which is appropriate for manipulation of quantum information. Despite advances in numerical methods to simulate the spectral properties of multi-element superconducting circuits, the literature lacks a consistent and effective method of determining the effective qubit Hamiltonian. Here we address this problem by introducing a novel local basis reduction method. This method does not require any ad hoc assumption on the structure of the Hamiltonian such as its linear response to applied fields. We numerically benchmark the local basis reduction method against other Hamiltonian reduction methods in the literature and show that it is applicable over a wider parameter range, particularly for superconducting qubits with reduced anharmonicity, including the capacitively-shunted flux qubit. By combining the local basis reduction method with the Schrieffer-Wolff transformation we further extend its applicability to systems of interacting qubits and use it to extract both non-stoquastic two-qubit Hamiltonians and three-local interaction terms in three-qubit Hamiltonians.
arxiv pdf