Quantum Knitting for Dummies

Abstract

Multidimensional tensor-network states, such as cluster states, are a key resource for quantum communication and measurement-based quantum computing. Recently, cluster states have been generated both in the microwave and optical regime but the generation of large-scale 2D cluster states in discrete-variable systems remains challenging. We present a superconducting device to enable the generation of two-dimensional tensor-network states of itinerant microwave photons. The device contains two long-lived storage qubits and two emitter qubits which rapidly decay into a waveguide. Two-qubit gates and deterministic photon emission are realized by parametric operations on tunable couplers. We demonstrate the emission of time-multiplexed photonic Bell states with fidelities above 94% and frequency-multiplexed two-photon cluster states with fidelities above 80%. These two types of entangled states constitute the building blocks for a prospective 2D cluster state. This is a step towards realizing universal measurement-based quantum computation and two-dimensional entanglement distribution throughout quantum networks in the microwave domain.