Hybrid digital-analog simulation of many-body dynamics with
  superconducting qubits
In recent years, there has been a significant progress in the development of
digital quantum processors. The state-of-the-art quantum devices are imperfect,
and fully-algorithmic fault-tolerant quantum computing is a matter of future.
Until technology develops to the state with practical error correction,
computational approaches other than the standard digital one can be used to
avoid execution of the most noisy quantum operations. We demonstrate how a
hybrid digital-analog approach allows simulating dynamics of a transverse-field
Ising model without standard two-qubit gates, which are currently one of the
most problematic building blocks of quantum circuits. We use qubit-qubit
crosstalks (couplings) of IBM superconducting quantum processors to simulate
Trotterized dynamics of spin clusters and then we compare the obtained results
with the results of conventional digital computation based on two-qubit gates
from the universal set. The comparison shows that digital-analog approach
significantly outperforms standard digital approach for this simulation
problem, despite of the fact that crosstalks in IBM quantum processors are
small. We argue that the efficiency of digital-analog quantum computing can be
improved with the help of more specialized processors, so that they can be used
to efficiently implement other quantum algorithms. This indicates the prospect
of a digital-to-analog strategy for near-term noisy intermediate-scale quantum
computers.
D. V. Babukhin A. A. Zhukov W. V. Pogosov