NISQperiood

NISQperiood, or the Noisy Intermediate-Scale Quantum era, refers to the current and near-future stage of quantum computing characterized by quantum processors that have tens to a few hundred qubits and are noisy, without scalable quantum error correction. The term was popularized by John Preskill in 2018 to describe systems that are large enough to be useful but too noisy to be scaled reliably without error correction.

Key features of the NISQ period include significant gate errors, decoherence times that limit circuit depth, imperfect readout, and the absence of scalable fault-tolerant architectures. These limitations constrain the complexity of executable circuits and the reliability of results, prompting researchers to pursue error mitigation and hybrid approaches rather than full fault-tolerant universal quantum computation.

Despite these constraints, NISQ devices are expected to demonstrate quantum advantage for selected tasks such as quantum simulation of molecules and materials, optimization, sampling, and certain machine-learning problems. Variational quantum algorithms, including the variational quantum eigensolver (VQE) and the quantum approximate optimization algorithm (QAOA), are commonly explored as practical near-term applications.

Milestones and debates within the period include claims of quantum supremacy or quantum advantage on specific tasks, progress across platforms such as superconducting qubits and trapped ions, and ongoing discussions about the scope and practicality of demonstrated advantages. Critics emphasize the limitations of current devices and the careful interpretation of any claimed advantage.

The long-term outlook aims at improving qubit quality, implementing effective error mitigation, and developing scalable architectures toward fault-tolerant quantum computing with logical qubits. The transition from the NISQ era to a fully fault-tolerant era remains uncertain and is a central focus of ongoing quantum research.