NISQ and chemistry
In my interview with Sam McArdle, we discussed NISQ as a method to make the most of "bad" qubits. In a typical logical qubit with error correction, you could have a small number of qubits doing the calculations, and a large army of qubits doing the error correction. For example, with surface code, you can have a thousand noisy qubits and one error-free qubit.
In NISQ though, we use the noisy qubits to do the calculations. As these qubits are noisy, the time taken to perform calculations must be short. If the calculations are not quick, we may end up with error-prone results. Typically, this setup would involve a shorter circuit and no error-correcting qubits. The system is re-initialized after every repetition to ensure errors do not build up.
As a result, we will need to use an approach that can accommodate lower coherence times. Coherence time just refers to the span that quantum states can survive for. Traditionally, an approach called quantum...
