rigetti / rigetti/pyquil

Behaviour of DELAY statement is inconsistent with documentation

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bug :bug:
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Description

Pre-Report Checklist

pyquil 3.0.0

Issue Description

In the documentation, the syntax for DELAY statements is as follows:

DELAY q0 q1 ... delay_in_s

https://pyquil-docs.rigetti.com/en/stable/apidocs/pyquil.gates.html#pyquil.gates.DELAY

It is also possible to delay all frames on some qubits, e.g. DELAY 0 1 2 1.0

or

PRAGMA q0 q1 "delay_in_s"

https://pyquil-docs.rigetti.com/en/stable/basics.html#asking-for-a-delay

However, the behaviour seems to follow the quilT specification:

https://github.com/quil-lang/quil/blob/master/rfcs/analog/proposal.md#delay

which doesn't apply the delay to q0 and q1, but only to instructions which include both q0 and q1.

Suggested fix

The documentation should be updated to make this more clear:

eg. Delay single-qubit gates on qubit 5 for 50ns

DELAY 5 50.0e-9

eg. Delay two-qubits gates on qubit 4/5 for 50ns

DELAY 4 5 50.0e-9

eg. Delay all gates on qubit 4/5 for 50ns

DELAY 4 50.0e-9
DELAY 5 50.0e-9
FENCE 4 5

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the DELAY API documentation and the “Asking for a delay” basics page linked in the issue, then compare their wording with the Quil delay specification. Update the documentation to distinguish delays on individual qubits, shared multi-qubit instructions, and all gates, using the examples provided. Verify that the documented behavior matches the specification.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
documentation, quantum-computing
Issue type
Documentation
Difficulty
2/5
Estimated time
1-3 hours
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
45/100

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