NISQ (noisy intermediate-scale quantum)

NISQ is the honest name for where quantum computing actually is right now. Picture a workshop full of brilliant but jittery hands: you have somewhere between roughly 50 and a few thousand qubits, which is the "intermediate scale" part, but every gate you apply and every moment that passes adds a little error, which is the "noisy" part. There is no full error correction running underneath to catch and fix those mistakes, so the longer and deeper your computation, the more the noise piles up until the answer drifts into nonsense.

The term was coined by physicist John Preskill in 2018, and it does real work by setting expectations. These machines are genuinely useful for experiments, for studying quantum systems, and for hybrid algorithms where a short quantum circuit hands results back to an ordinary computer that steers the next step. What they cannot yet do is run the long, deep circuits that headline tasks like Shor-scale factoring demand. Those require fault-tolerant qubits that survive thousands or millions of operations, and that hardware does not exist today.

So when you hear that a chip has hundreds of qubits, the useful question is not just "how many?" but "how good?" A handful of clean, long-lived qubits can outperform a large pile of noisy ones. NISQ is a stepping stone, not the destination, and being clear-eyed about its limits is part of taking the field seriously.