[Frontend][Runtime] lightning.qubit specifies its supported capabilities, compilation options, and runtime options in a config file

[erick-xanadu]

Context:

Description of the Change:

• Device specification for lightning.qubit is available.
• Device specification for lightning.kokkos is available.
• Device specification for braket.local.qubit device is available.
• Device specification for braket.aws.qubit device is available.
• Device specification for dummy.device is available
• Check validity by
  • checking if existing file exists
  • check if gates in "native", "decomp" and "matrix" overlap
  • check if gates in "native", "decomp" and "matrix" do not match with those in qml.device.operations
• Support custom devices.
• decomposition to QubitUnitary may be specified by "matrix" gates in the specification.
  • However, to maintain maximum differentiability at the moment this is overriden by the compiler.
• Users can specify compilation options/details, which will be taken into account by the compiler.
  • We don't have any compilation options at the moment that fit in this scope.
• Users can specify Lightning runtime options within the device loader, as allowed by the configuration, which will be taken into account at runtime (for example, MCMC sampling).
  • options are encoded in the IR
  • options are used in the device
  • options are tested
• Documentation
• After discussion, do not install these files in Catalyst, have them be accessible from qml.Device.
  • PR for changes in lightning Adds Catalyst specification files. pennylane-lightning#566
  • Update dummy device to use field with path to config file.

Benefits:

• Implementation of ADR. Please see ADR 73 for the details.

Possible Drawbacks:

• Now tests for custom devices require toml files as well.

Related GitHub Issues:

Notes:

• We should consider merging this one before Adds Catalyst specification files. pennylane-lightning#566 and then just changing the location of the config file once we sync up.

[sc-46420]

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (980f584) 99.49% compared to head (a721451) 99.54%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #369      +/-   ##
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+ Coverage   99.49%   99.54%   +0.05%     
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  Files          42       43       +1     
  Lines        7150     7302     +152     
  Branches      483      497      +14     
==========================================
+ Hits         7114     7269     +155     
+ Misses         20       17       -3     
  Partials       16       16              

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[dime10]

Great work @erick-xanadu, from my side this looks good 💯

I just wanted to clarify, what is the strategy we have to remove the lightning toml files from our repo (since we could already build the runtime against the latest lightning commit)? Does it require that the installed user package of lightning is the latest?

[erick-xanadu]

@dime10 feel free to add more suggestions. Will merge by the end of the day.

[dime10]

All good from my end 👍