The NISQ era refers to the “Noisy Intermediate-Scale Quantum” phase of quantum computing development. The term was popularized by John Preskill, a renowned physicist, in a 2018 paper. The term reflects the current state of quantum machines which are still going through a phase of evolution. The term Noisy and Intermediate – Scale in NISQ refer to:

Noisy: Current quantum computers are prone to errors because their qubits (quantum bits) are sensitive to all sorts of disturbances from their environment. This “noise” can lead to computation errors.

Intermediate-Scale: This indicates that the quantum computers of this era are larger than the small proof-of-principle machines (which might have only a few qubits), but they are not yet at the large, fault-tolerant scale that would be required for many practical, game-changing applications.

The NISQ era is characterized by quantum computers that have between 50 to a few hundred qubits. While they are noisy and lack full error correction, they may still be capable of performing certain tasks more efficiently than classical computers, especially in areas like quantum simulation and optimization.

During the NISQ era, researchers and industries are primarily focused on:

1. Understanding and mitigating noise: This involves both hardware innovations and the development of algorithms that are noise-resilient.
2. Exploring practical applications: Even with their limitations, NISQ computers might offer advantages in some niche areas over classical computers.
3. Quantum software and algorithms: Development of specialized algorithms that can run efficiently on NISQ machines.
4. Error correction: While full error correction might be beyond the capabilities of NISQ devices, some rudimentary error correction and error mitigation techniques are being explored.

The transition beyond the NISQ era would likely involve the development of large-scale, fault-tolerant quantum computers, which would be a significant leap in quantum computing capabilities.