Add 2q fractional gates to the `UnitarySynthesis` transpiler pass #13568

ShellyGarion · 2024-12-16T11:06:40Z

Summary

With the introduction of new 2q-fractional gates, such as RZZGate as part of the QPU, we add them to the UnitarySynthesis transpiler pass.
https://www.ibm.com/quantum/blog/fractional-gates

Details and comments

qiskit-bot · 2024-12-16T11:06:45Z

One or more of the following people are relevant to this code:

@Qiskit/terra-core
@levbishop

coveralls · 2024-12-16T13:24:13Z

Pull Request Test Coverage Report for Build 13237385047

Details

235 of 246 (95.53%) changed or added relevant lines in 4 files are covered.
19 unchanged lines in 3 files lost coverage.
Overall coverage increased (+0.02%) to 88.313%

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/accelerate/src/unitary_synthesis.rs	119	124	95.97%
crates/accelerate/src/two_qubit_decompose.rs	104	110	94.55%

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	2	93.29%
crates/qasm2/src/lex.rs	5	92.48%
crates/qasm2/src/parse.rs	12	97.15%

Totals
Change from base Build 13204846880:	0.02%
Covered Lines:	78777
Relevant Lines:	89202

💛 - Coveralls

qiskit/transpiler/passes/synthesis/unitary_synthesis.py

ElePT

Hi @ShellyGarion! thanks for opening the PR, I left a couple of preliminary comments. I hope they make sense :)

qiskit/transpiler/passes/synthesis/unitary_synthesis.py

qiskit/synthesis/two_qubit/two_qubit_decompose.py

qiskit/transpiler/passes/synthesis/unitary_synthesis.py

crates/accelerate/src/unitary_synthesis.rs

ShellyGarion · 2025-01-23T06:58:13Z

I think this closes #13428. How about adding a test case of consecutive RZZ (RXX, and RYY) gates?

@t-imamichi - unfortunately this PR does not close #13428 yet, since the ConsolidateBlocks transpiler pass does not consolidate the consecutive RZZ gates into a single unitary.
This should be fixed in #13419.
I will therefore transfer your comment there.

ElePT

Thanks for the tests! I took a look and they look good to me.

test/python/transpiler/test_unitary_synthesis.py

crates/accelerate/src/two_qubit_decompose.rs

mtreinish · 2025-01-27T16:19:26Z

crates/accelerate/src/two_qubit_decompose.rs

@@ -2516,7 +2517,7 @@ impl TwoQubitControlledUDecomposer {
                        .collect::<SmallVec<_>>();
                    Ok((Some(inv_gate.0), inv_gate_params, qubits))
                }
-                RXXEquivalent::CustomPython(gate_cls) => {
+                RXXEquivalent::CustomPython(gate_cls) => Python::with_gil(|py: Python| {


I'm fine with this changes since longer term we'll need to do this when running this in a parallel context. But I'm curious what prompted these changes?

See the discussion here: #13568 (comment)
I wanted to have a purely-rust new_inner function, so I copied the solution from your PR :)

mtreinish · 2025-01-27T16:54:40Z

qiskit/synthesis/two_qubit/two_qubit_decompose.py

@@ -270,32 +270,46 @@ class TwoQubitControlledUDecomposer:
    :math:`U \sim U_d(\alpha, 0, 0) \sim \text{Ctrl-U}`
    gate that is locally equivalent to an :class:`.RXXGate`."""

-    def __init__(self, rxx_equivalent_gate: Type[Gate]):
+    def __init__(self, rxx_equivalent_gate: Type[Gate], euler_basis: str = "ZYZ"):
        r"""Initialize the KAK decomposition.


I would avoid changing the defaults for any other classes it causes necessary churn. I think the choice was more just out of habit/standard gates to use. In this case using zxz as the default is fine since it's new, (although I'd be inclined to use zsxx as the default). But it doesn't really matter because either you don't care about the euler basis, or you do and you will specify it.

… address TwoQubitControlledUDecomposer issue, it appends gates outside of basis set (h/s/sdg)

ElePT

Hi @ShellyGarion, I have pushed a commit that includes the work I had been doing on integrating non-standard gates. As you know, I included a couple of unit tests which have pointed to a new issue we hadn't realized until now. Even though the CI checks might not fully pass I wanted to expose this commit to make sure we could all look for solutions with the latest information.

ElePT · 2025-01-29T16:51:43Z

test/python/transpiler/test_unitary_synthesis.py

+        # TODO: fix this assertion
+        # opcount = qc_transpiled.count_ops()
+        # print(opcount)
+        # self.assertTrue(set(opcount).issubset({"rz", "rx", CustomXXGate.name}))
+        # self.assertTrue(np.allclose(Operator(qc_transpiled), Operator(qc)))


This test has unveiled an issue with the integration of the TwoQubitControlledUDecomposer. The expectation for the unitary synthesis pass is that the decomposed circuit will respect the user-given basis gates (directly or through a target). However, the TwoQubitControlledUDecomposer will always append a series of h, s and sdg to convert from the canonical form to the given basis. We could only run the decomposer if the target basis gates contain h, s and sdg, but this would leave out essentially all IBM backends. After discussing it with @Cryoris we think it might make sense to express this conversion from canonical form in terms of ibm-supported basis gates, which doesn't fix the issue completely, but would make the pass more usable in the current scenarios we know. If we did that, we could follow this simple logic where we run the decomposer when the gates used match the given basis set. What do you think?

As there are only 12 euler bases to pick from in the 1q decomposer I think the approach I would look at here would be to just make a small lookup table in for each of the euler basis values and then substitute in the appropriate gates based on the selected euler basis. For example in the two qubit decomposer define something like:

static S_GATE_LUT = [[Option<(StandardGate, [f64; 3])>; 3]; EULER_BASIS_SIZE] = [[Some((StandardGate::U3, [0.,0.,PI_2]), None, None], ...]

for all 3 gates. Then in the current code where it's adding the gates just do a lookup with S_GATE_LUT[self.euler_basis as usize] and add the gates to the output accordingly. That should minimize the overhead here but meet the expectations of the transpiler pass.

Thanks @ElePT for adding the code and tests, and @mtreinish for your suggestion!
So this update should be done in the file two_qubit_decompose.rs when we add the gates S, Sdg and H?
Is there a reason not to use the unitary_to_gate_sequence_inner to decompose the matrices of the S, Sdg and H gates? (so we wouldn't need to update the static array if we add another euler basis)

The new test runs UnitarySynthesis in isolation while test_parameterized_basis_gate_in_target runs the full transpiler pipeline, it looks like these gates are translated in later stages and that's why they don't show up in the final result. The test with the custom gate fails if you try to run transpile because the basis translator doesn't know how to handle the circuit. However, even if the pipeline compensates the extra gates, I think the pass in isolation should work following the assumptions (i.e. it should follow the specified basis).

see 5bb55b5
I decomposed the S, Sdg and H gates using unitary_to_gate_sequence_inner (which is more general then having lookup tables)

@ElePT - following your question below. I think that the correct place to add lookup tables for non-parametric 1-qubit gates (like S, Sdg and H) is in the function unitary_to_gate_sequence_inner, since the two_qubit_decompose code should handle 2-qubit gates and not 1-qubit gates.
I'm not sure how much it will impact the performance here (since we need to decompose other 1-qubit and 2-qubit gates). We can consider it in a follow-up PR.

after talking with @mtreinish I don't think that the one-qubit synthesis is a bottleneck since it should be negligible compared to the two-qubit synthesis. We can still improve it in a follow-up PR if needed.

test/python/transpiler/test_unitary_synthesis.py

ElePT

I think that the PR is in a good state, the functionality is covered and tested. Some parts of the code could be cleaned up (like my score_instruction comment), but this could be done in a follow-up (I will have to refactor the code a bit to add support for basis_gates inputs anyway). The only open point would be the performance of the pass, and the use of the lookup table vs the euler decomposer. I believe that the lookup table will be faster, @ShellyGarion, and the likelihood of adding a new basis to the euler list I think is pretty low. Would you be willing to give it a try?

releasenotes/notes/add-2q-fractional-gates-to-unitarysynthesis-pass-f66eee29903f5639.yaml

ElePT · 2025-02-04T10:15:00Z

releasenotes/notes/add-2q-fractional-gates-to-unitarysynthesis-pass-f66eee29903f5639.yaml

+    Add two-qubit fractional basis gates, such as :class:`.RZZGate`, to the
+    :class:`.UnitarySynthesis` transpiler pass.


Same comment as above, we should add an example usage.

Suggested change

Add two-qubit fractional basis gates, such as :class:`.RZZGate`, to the

:class:`.UnitarySynthesis` transpiler pass.

Added support for two-qubit fractional basis gates, such as :class:`.RZZGate`, to the

:class:`.UnitarySynthesis` transpiler pass. The decomposition is done using the :class:`.TwoQubitControlledUDecomposer`, and supports both standard and custom basis gates.

done in 55556f8

ElePT

Approving, as this will unblock follow-up work.

TwoQubitControlledUDecomposer to _decomposer_2q_from_basis_gates

89ca81e

ShellyGarion added the mod: transpiler Issues and PRs related to Transpiler label Dec 16, 2024

ShellyGarion added this to the 2.0.0 milestone Dec 16, 2024

ShellyGarion requested a review from ElePT December 16, 2024 11:06

ShellyGarion requested review from alexanderivrii and a team as code owners December 16, 2024 11:06

ElePT self-assigned this Dec 16, 2024

update (temporarily) basis gates in test

077ecb9

gadial reviewed Dec 17, 2024

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ElePT reviewed Dec 17, 2024

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minor fix

18b20f6

ElePT mentioned this pull request Dec 19, 2024

Small refactoring of unitary synthesis tests #13582

Merged

ShellyGarion and others added 13 commits December 19, 2024 06:49

add EulerBasis as a parameter to TwoQubitControlledUDecomposer

967da13

fix global_phase calculation in TwoQubitContolledUDecomposer

3bb10fd

add TwoQubitControlledUDecomposer to the docs

14c7aac

make the choice of kak_gate deterministic

eeff4cd

Merge branch 'main' into unitary_synth

043a795

remove XXDecomposer from _decomposer_2q_from_basis_gates

b94070a

make call_inner pub, add Clone, Debug

0a1644b

add TwoQubitControlledUDecomposer to unitary_synthesis.rs

48fec9b

merge main branch, fix conflict

009d87e

Fix exit condition for GOODBYE_SET and PARAM_SET

85e2962

fix conflict with main branch

c5d0c97

make DEFAULT_ATOL public

d7b84e9

add TwoQubitControlledUDecomposer to synth_su4_sequence

ea9a2d0

ShellyGarion commented Jan 16, 2025

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ElePT mentioned this pull request Jan 21, 2025

Remove use of BackendProperties (BackendV1) in UnitarySynthesis pass #13706

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ShellyGarion mentioned this pull request Jan 23, 2025

[WIP] Add new multithreaded TwoQubitPeepholeOptimization pass #13419

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6 tasks

ShellyGarion added 6 commits January 23, 2025 02:25

remove using py in rust functions

231af7f

minor update to test

bb874c1

make atol optional

c2a9ad4

fix conflict with main branch

d39c005

add a test with fractional gates in the backend

106ae4a

add release notes

9131e3d

ElePT reviewed Jan 24, 2025

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enhance tests following review

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mtreinish reviewed Jan 27, 2025

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ElePT changed the title ~~Add 2q fractional gates to the UnitarySynthesis tranpiler pass~~ Add 2q fractional gates to the UnitarySynthesis transpiler pass Jan 29, 2025

Add support for non-standard parametrized gates, add new tests. TODO:…

23b9e6b

… address TwoQubitControlledUDecomposer issue, it appends gates outside of basis set (h/s/sdg)

ElePT reviewed Jan 29, 2025

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ShellyGarion added 2 commits January 30, 2025 08:46

decompose S, Sdg, H into euler_basis

5bb55b5

update test

f4da2da

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Investigate porting unitary synthesis to rust #8774

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Overwrite Python-side gate parameters as well as Rust-side parameters.

1bd71c5

ShellyGarion requested review from ElePT and mtreinish February 4, 2025 07:19

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fix conflict with mai branchn

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add examples to release notes

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ElePT added this pull request to the merge queue Feb 10, 2025

Merged via the queue into Qiskit:main with commit 02850cf Feb 10, 2025
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Add 2q fractional gates to the `UnitarySynthesis` transpiler pass #13568

Add 2q fractional gates to the `UnitarySynthesis` transpiler pass #13568

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		Add two-qubit fractional basis gates, such as :class:`.RZZGate`, to the
		:class:`.UnitarySynthesis` transpiler pass.

Add 2q fractional gates to the UnitarySynthesis transpiler pass #13568

Add 2q fractional gates to the UnitarySynthesis transpiler pass #13568

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ShellyGarion commented Dec 16, 2024

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Add 2q fractional gates to the `UnitarySynthesis` transpiler pass #13568

Add 2q fractional gates to the `UnitarySynthesis` transpiler pass #13568

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