UserWarning: SIMPLE-WARNING: Chip specification contained fidelity 1.0d0 > 1.

[braised-babbage]

Issue Description

Several tests get this warning. It is not apparent why, considering the specs_dict in conftest.py does not contain any fidelities greater than 1.

How to Reproduce

To pick one example:

(pyquil) erik-macbook:pyquil erik$ pytest pyquil/tests/test_quantum_computer.py::test_qc
===================================== test session starts ======================================
platform darwin -- Python 3.7.4, pytest-5.1.2, py-1.8.0, pluggy-0.13.0
rootdir: /Users/erik/src/pyquil
plugins: requests-mock-1.7.0, timeout-1.3.3, rerunfailures-7.0
collected 1 item

pyquil/tests/test_quantum_computer.py .                                                  [100%]

======================================= warnings summary =======================================
pyquil/tests/test_quantum_computer.py::test_qc
  /Users/erik/miniconda3/envs/pyquil/lib/python3.7/site-packages/rpcq/_client.py:177: UserWarning: SIMPLE-WARNING: Chip specification contained fidelity 1.0d0 > 1. Truncating to 0.99999d0.
    warn(f"{warning.kind}: {warning.body}")

-- Docs: https://docs.pytest.org/en/latest/warnings.html
================================ 1 passed, 1 warnings in 0.10s =================================

[notmgsk]

Are the tests pulling data from https://forest-server.qcs.rigetti.com?

[notmgsk]

It looks like if a gate fidelity is not present, then it is assigned PERFECT_FIDELITY = 1.0 https://github.com/rigetti/pyquil/blob/master/pyquil/device.py#L565

[braised-babbage]

Ah, so this is a quilc thing...

(defconstant +near-perfect-fidelity+ 0.99999d0
  "Even perfect operations are typically limited in their physical realization by, say, the granularity of control electronics. (For instance, waveform IQ values might be stored as complex fixnums of some specified depth.) This constant is a mnemonic for \"supposedly perfect\" and captures some of the loss incurred by these imperfections.")

[notmgsk]

Ah, so this is a quilc thing...

(defconstant +near-perfect-fidelity+ 0.99999d0
  "Even perfect operations are typically limited in their physical realization by, say, the granularity of control electronics. (For instance, waveform IQ values might be stored as complex fixnums of some specified depth.) This constant is a mnemonic for \"supposedly perfect\" and captures some of the loss incurred by these imperfections.")

As I understand it (almost verbatim from @ecpeterson), this is because the compiler will for

• a fidelity of 1.0 not eliminate the instruction; or for
• a fidelity >1.0 actively try to introduce the instruction.