ADAPT: Mitigating Idling Errors in Qubits via Adaptive Dynamical
  Decoupling
The fidelity of applications on near-term quantum computers is limited by
hardware errors. In addition to errors that occur during gate and measurement
operations, a qubit is susceptible to idling errors, which occur when the qubit
is idle and not actively undergoing any operations. To mitigate idling errors,
prior works in the quantum devices community have proposed Dynamical Decoupling
(DD), that reduces stray noise on idle qubits by continuously executing a
specific sequence of single-qubit operations that effectively behave as an
identity gate. Unfortunately, existing DD protocols have been primarily studied
for individual qubits and their efficacy at the application-level is not yet
fully understood.
  Our experiments show that naively enabling DD for every idle qubit does not
necessarily improve fidelity. While DD reduces the idling error-rates for some
qubits, it increases the overall error-rate for others due to the additional
operations of the DD protocol. Furthermore, idling errors are program-specific
and the set of qubits that benefit from DD changes with each program. To enable
robust use of DD, we propose Adaptive Dynamical Decoupling (ADAPT), a software
framework that estimates the efficacy of DD for each qubit combination and
judiciously applies DD only to the subset of qubits that provide the most
benefit. ADAPT employs a Decoy Circuit, which is structurally similar to the
original program but with a known solution, to identify the DD sequence that
maximizes the fidelity. To avoid the exponential search of all possible DD
combinations, ADAPT employs a localized algorithm that has linear complexity in
the number of qubits. Our experiments on IBM quantum machines (with 16-27
qubits) show that ADAPT improves the application fidelity by 1.86x on average
and up-to 5.73x compared to no DD and by 1.2x compared to DD on all qubits.
Poulami Das Swamit Tannu Siddharth Dangwal Moinuddin Qureshi