Implementation of pairwise longitudinal coupling in a three-qubit   superconducting circuit
  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. 
Tanay Roy, Suman Kundu, Madhavi Chand, Sumeru Hazra, N. Nehra, R.   Cosmic, A. Ranadive, Meghan P. Patankar, Kedar Damle, R....
quant-ph cond-mat.mes-hall