What is a "shot" in relation to quantum computing? I heard it is repeating time, but I don't understand it. Additionally, why is the default number of shots 1,024 in the IBM Q Experience?
One more question - I saw the sentence for each value of the shots, the experiment repeated 100 times. What is this mean? Is there difference between shots and repeated experiments? Are shot and experiment repetition same thing?
Number of shots: Number of shots means how many times an algorithm is run to get a probability distribution of results.
Experiment is repeated: This means how many times an experiment is repeated with particular number of shots. Imagine, you repeated an experiment 100 times and you have 1,024 shots. In each experiement repetition some metrics is calculated based on probability distribution obtained from 1,024 shots (i.e. an algorithm repetitions). The metrics can be, for example expected value or any other metrics based on the results. Hence you have 100 values of the metric and you can do some statistics on them.
Overall, number of shots and experiment repetitions mean different things.
Default number of shots: IBM Q allows you to set different number of shots. Default value 1,024 is an arbitrary decision. There is no physical/technical reason for that value.
"A shot is a single execution of a quantum algorithm on a QPU. For example, a shot is a single pass through each stage of a complete quantum circuit on a gate-based QPU"
From https://aws.amazon.com/braket/pricing/
It seems that the definition of a shot becomes very important when money is involved. :)
Shots are implementations of identical experiments that have same algorithm and same parameters (initial states). However, we can repeat experiments with different parameters while we keep number of shots the same for each experiment.
