A fully programmable three-qubit superconducting processor with all-to-all longitudinal coupling*

We recently introduced the “trimon”, a longitudinally coupled three-qubit system based on a multi-mode superconducting circuit. Single-pulse implementation of the Toffoli gate and all-to-all coupling enables universal programmability of the processor. We will first describe how we can reconstruct the density matrix for a three-qubit state using a joint readout scheme. We will then discuss the performance of the elementary controlled-controlled-NOT (CCNOT) gate and the preparation of high-fidelity, two- and three-qubit entangled states. Another unique feature of this system is the ability to implement error-free CCZ gate which simplifies construction of various quantum oracles. We will demonstrate these capabilities by executing various quantum algorithms like Deutsch-Jozsa, Bernstein-Vazirani, Grover, period-finding etc. Finally, we will discuss the possibility of building larger quantum processors using the trimon as a building block.
Reference: Phys. Rev. Applied 7 (5), 054025