  Quantum computers in the NISQ era are prone to noise. A range of quantum
error mitigation techniques has been proposed to address this issue. Zero-noise
extrapolation (ZNE) stands out as a promising one. ZNE involves increasing the
noise levels in a circuit and then using extrapolation to infer the zero noise
case from the noisy results obtained. This paper presents a novel ZNE approach
that does not require circuit folding or noise scaling to mitigate depolarizing
and/or decoherence noise.
  To mitigate depolarizing noise, we propose leveraging the extreme/infinite
noisy case, which allows us to avoid circuit folding. Specifically, the circuit
output with extreme noise becomes the maximally mixed state. We show that using
circuit-reliability metrics, simple linear extrapolation can effectively
mitigate depolarizing noise. With decoherence noise, different states decay
into the all-zero state at a rate that depends on the number of excited states
and time. Therefore, we propose a state- and latency-aware exponential
extrapolation that does not involve folding or scaling. When dealing with a
quantum system affected by both decoherence and depolarizing noise, we propose
to use our two mitigation techniques in sequence: first applying decoherence
error mitigation, followed by depolarizing error mitigation.
  A common limitation of ZNE schemes is that if the circuit of interest suffers
from high noise, scaling-up noise levels could not provide useful data for
extrapolation. We propose using circuit-cut techniques to break a large quantum
circuit into smaller sub-circuits to overcome this limitation. This way, the
noise levels of the sub-circuits are lower than the original circuit, and ZNE
can become more effective in mitigating their noises.
