Kedar Damle

Multi-mode superconducting circuits for realizing strongly coupled multi-qubit processor units

  1. Tanay Roy,
  2. Madhavi Chand,
  3. Sumeru Hazra,
  4. Suman Kundu,
  5. Kedar Damle,
  6. and R. Vijay
Inter-qubit coupling and qubit connectivity in a processor are crucial for achieving high fidelity multi-qubit gates and efficient implementation of quantum algorithms. Typical superconducting
processors employ relatively weak transverse inter-qubit coupling which are activated via frequency tuning or microwave drives. Here, we propose a class of multi-mode superconducting circuits which realize multiple transmon qubits with all-to-all longitudinal coupling. These „artificial molecules“ directly implement a multi-dimensional Hilbert space that can be easily manipulated due to the always-on longitudinal coupling. We describe the basic technique to analyze such circuits, compute the relevant properties and discuss how to optimize them to create efficient small-scale quantum processors with universal programmability.
arxiv pdf

Implementation of pairwise longitudinal coupling in a three-qubit superconducting circuit

  1. Tanay Roy,
  2. Suman Kundu,
  3. Madhavi Chand,
  4. Sumeru Hazra,
  5. N. Nehra,
  6. R. Cosmic,
  7. A. Ranadive,
  8. Meghan P. Patankar,
  9. Kedar Damle,
  10. and R. Vijay
We present the „trimon“, a multi-mode superconducting circuit implementing three qubits with all-to-all longitudinal coupling. This always-on interaction enables simple
implementation of generalized controlled-NOT gates which form a universal set. Further, two of the three qubits are protected against Purcell decay while retaining measurability. We demonstrate high-fidelity state swapping operations between two qubits and characterize the coupling of all three qubits to a neighbouring transmon qubit. Our results offer a new paradigm for multi-qubit architecture with applications in quantum error correction, quantum simulations and quantum annealing.
arxiv pdf