Tagging qubits and moments

[balopat]

Feature: Tagging qubits and moments

Problem: Currently one can tag operations. These can serve as compiler or executor pragmas. They also provide a way to cross an api boundary with more generic data appropriately serialized. In actual hardware, it is useful to also provide other metadata to the hardware. For example qubit can be tagged with properties of the qubit necessary for executing gates. Similarly tagging moments can be useful to propagate information about the duration of the moment upwards and downwards through the api surface.

Rough requirements:

• Decide whether tagging pattern for operations is the correct one to follow
• Identify use cases to ensure it will be a used feature
• Implement tagging in qubit and moments, and potentially on new subcircuit constructions (https://github.com/quantumlib/Cirq/issues/3614)

[github-actions[bot]]

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[mhucka]

This issue came up recently. People feel there is a need for this, and in fact they want it rather soon. Putting it on the 2025 roadmap too.

[mhucka]

This has been done.