Remove subsystem_labels option from DynamicsBackend #248

DanPuzzuoli · 2023-07-18T20:46:38Z

Summary

Closes #235

Details and comments (out of date, see next comment)

This is currently a draft to prototype a potential solution to #235, in which the subsystem_labels option is removed, and all qubits removed via the subsystem_list argument of from_backend are actually "kept" as trivial 1-dimensional systems.

So far:

I've commented out all lines/blocks using subsystem_labels.
Where necessary, new code has been added, e.g. construction of subsystem_dims in from_backend has been changed to include all pre-existing subsystems, but setting the dimension of the "removed" subsystems to 1 (instead of not including them at all).

Initial testing in a jupyter notebook seems to indicate that this behaves as expected:

I can do from_backend with a non-trivial subsystem_list, and the backend is built without issue.
I haven't yet done any verifications of correctness, but it seems like we can run sims and compute measurement results as well.

To do:

Add number of qubits to the backend wherever it makes sense.
Do some initial verification that the calculations are correct.
The subsystem_labels option was used to raise errors of non-existent subsystems were measured. As this no longer exists, it would be nice to still warn users if their schedule measures a trivial subsystem.
- This could just be done by checking the dimension of the measured subsystem.
Pre-existing tests need to be modified.

Question:

This will remove the subsystem_labels option. I'm not sure how this could be deprecated, because it will literally serve no purpose and have no effect anymore.

DanPuzzuoli · 2023-07-19T15:11:52Z

I've now implemented all of the above changes. Here is the summary:

subsystem_labels has been removed from the DynamicsBackend options. Now, we will always view the labels of subsystems in DynamicsBackend as being of the form [0, ..., num_qubits - 1].
This option was used in DynamicsBakend.from_backend - the argument subsystem_list was stored in subsystem_labels to keep track of which subsystems were kept. With this being removed now, the returned DynamicsBackend instead "keeps" the removed subsystems (the returned backend still looks like it has all qubits), but treats them as trivial by listing their dimension as 1 in the subsystem_dims argument.

Luckily this change doesn't impact any of the numerical functionality. In addition to the above:

Error checking/raising involving subsystem_labels have been changed. E.g. now, rather than checking if an index is in subsystem_labels it will check if it's < len(subsystem_dims).
A warning has been added if a trivial subsystem (with dimension 1) is being measured.
I've modified and added tests to check for the above behaviour.

I've also added an upgrade release note explaining this change.

to24toro · 2023-07-21T05:06:08Z

qiskit_dynamics/backend/dynamics_backend.py

-    * ``subsystem_labels``: Integer labels for subsystems. Defaults to ``[0, ...,
-      len(subsystem_dims) - 1]``.
-    * ``meas_map``: Measurement map. Defaults to ``[[idx] for idx in subsystem_labels]``.
+    * ``meas_map``: Measurement map. Defaults to ``[[idx] for idx in range(len(subsystem_dims))]``.


[Q] What is meas_map in dynamicsbackend used for ? For bacekndV1 or backendV2 affinity?

I always forget exactly how meas_map works. DynamicsBackend itself doesn't use meas_map, but I think it's required by transpilation and/or pulse schedule validation. I believe the default meas_map described here allows measurements of any subset of qubits to pass the validation checks.

The meas_map is used for mapping qubits which have to be measured concurrently. The configuration of meas_map used here indicates each qubit can be measured independently.

Just asking, I just understood the need for transpile and pulse validation. Thanks.

to24toro · 2023-07-21T08:06:50Z

test/dynamics/backend/test_dynamics_backend.py

+            pulse.play(pulse.Waveform([0.5, 0.5, 0.5]), pulse.DriveChannel(0))
+            pulse.acquire(duration=1, qubit_or_channel=1, register=pulse.MemorySlot(0))
+
+        self.simple_backend.set_options(subsystem_dims=[2, 1])


[Q] What situation is the case that specifying explicitly one of subsystem_dims is 1?

For now I'm putting this test primarily to have a direct/explicit test of how this option behaves on it's own (not just within from_backend). Maybe a user would want to do this if they are building a custom model for a backend (but again don't want to model every single qubit, as in from_backend).

If users use like

backend= DynamicsBackend.from_backend(FakeKolkata(), subsystem_list=[1])

do they observe the warning?
If so, I'm not sure why this is necessary.

The warning will be raised if they do

backend= DynamicsBackend.from_backend(FakeKolkata(), subsystem_list=[1])

then submit a schedule or circuit that measures qubit 0. I was imagining in this case that we should let users know that they're measuring a system that has no evolution (which I thought could confuse users if no warning were present).

to24toro

LGTM!

…#248)

* adding sympy as an explicit requirement (#233) * Add warning for JAX versions on import of Dynamics (#232) * Add probability normalization to DynamicsBackend sampling routine (#239) * Add warning if digital carrier exceeds Nyquist frequency in pulse -> signal conversion (#242) * Fix bug with carrier_freq being a JAX tracer if envelope is constant in Signal (#247) * Remove subsystem_labels option from DynamicsBackend (#248) * Rename subsystem_dims Dict to subsystem_dims_dict (#250) * Fix ClassicalRegister counting in DynamicsBackend (#252) * temporary fix for docs (#253) * Drop support for backendV2 in from_backend (#249) * incrementing version number * cleaning up reno files --------- Co-authored-by: Kento Ueda <38037695+to24toro@users.noreply.github.com>

DanPuzzuoli added 6 commits July 18, 2023 16:30

initial attempted hack to remove subsystem_labels

c5df5f1

removing break point

bf4a6bf

added measurement instruction validation and tests

cd8cbe5

removing all temporary comments

29dbb34

formatting

54f226b

adding release note

0d91176

DanPuzzuoli changed the title ~~Proposed solution to #235~~ Remove subsystem_labels option from DynamicsBackend Jul 19, 2023

DanPuzzuoli marked this pull request as ready for review July 19, 2023 15:18

to24toro reviewed Jul 21, 2023

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to24toro mentioned this pull request Jul 21, 2023

Rename subsystem_dims of Dict to subsystem_dims_dict #250

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Merge branch 'main' into subsystem_list-change

7cd169c

to24toro mentioned this pull request Jul 21, 2023

Drop support for backendV2 in from_backend and _to_schedule_list #249

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to24toro approved these changes Jul 24, 2023

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DanPuzzuoli merged commit 577260b into qiskit-community:main Jul 24, 2023

DanPuzzuoli added a commit to DanPuzzuoli/qiskit-dynamics that referenced this pull request Aug 2, 2023

Remove subsystem_labels option from DynamicsBackend (qiskit-community…

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…#248)

DanPuzzuoli mentioned this pull request Jan 8, 2024

fix sub_dims bug in _get_iq_data #297

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Remove subsystem_labels option from DynamicsBackend #248

Remove subsystem_labels option from DynamicsBackend #248

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Remove subsystem_labels option from DynamicsBackend #248

Remove subsystem_labels option from DynamicsBackend #248

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DanPuzzuoli commented Jul 18, 2023 • edited Loading

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