Multi-spin measurements for quantum annealing

Measurements of multi-spin operators are expected to play an important role for quantum annealing, in applications including verification of entanglement, probing noise, and operation with feedback. We discuss the implementation of multi-spin measurements, with focus on annealing based on superconducting flux qubits. We identify a connection between multi-spin interactions and measurements, which helps designing the latter. We present in detail implementations of ZZ and ZZZ measurements, and comment on other types of measurements. We discuss also the prospects for integration and operation of multi-spin readout in a functional quantum annealer. The research is based upon work (partially) supported by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), via the U.S. Army Research Office contract W911NF-17-C-0050. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the ODNI, IARPA, or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright annotation thereon.