Pauli measurement #5311

yaelbh · 2020-10-29T10:09:24Z

Reviving #4024.

The conversation of #4024 dealt with the addition of gates after measurement. When does the removal of such gates, after final measurements, occur? The output of transpile still contains the gates after the final measurement.

To do items:

Store the basis in the instruction parameters, instead of the instruction name.
~~Allow also measurement in the I basis (no measurement).~~
Verify that works well when measuring multiple qubits.

add initial attempt at measurements

implement BasisTransformationMeasurement

its probably safer to wrap the Measure instruction if the basis is Z instead of the PauliMeasure to mimic the Measure instruction. Otherwise we might run into unforeseen issues since Measure might be used as primitive somewhere down in Terra

Move to PauliMeasure

* use clifford gates only * apply inverse post rotations for correct statevector simulations * make basis argument required * change to uppercase labels (but support lowercase still)

Apply Chris' suggestions

…i-measure

yaelbh · 2021-10-03T09:04:12Z

A few comments:

I didn't add support to measure_pauli in qasm.
I touched only a little the transpiler. I don't know which node is created in the DAG, in the presence of the new measure_pauli instruction, and what's its type (see for example _process_node and _process_measure in qiskit/converters/ast_to_dag.py). Checks whether something is a measurement appear all over, and I mostly didn't change them, I don't know if a change is required there, and if yes then how: in gate translations; in decisions related to optimization that are based on the number of measurements; and in passes: RemoveDiagonalGatesBeforeMeasure, AlignMeasures, BarrierBeforeFinalMeasurements, RemoveFinalMeasurements, OptimizeSwapBeforeMeasure.
I touched only a little the visualization. I tried my best with matplotlib, but didn't change text and latex. Note that, unlike measure, measure_pauli can take multiple qubits.

coveralls · 2021-11-22T11:40:32Z

Pull Request Test Coverage Report for Build 1489887938

53 of 67 (79.1%) changed or added relevant lines in 8 files are covered.
No unchanged relevant lines lost coverage.
Overall coverage increased (+0.006%) to 82.565%

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
qiskit/circuit/measure.py	30	32	93.75%
qiskit/visualization/text.py	12	14	85.71%
qiskit/visualization/matplotlib.py	2	12	16.67%

Totals
Change from base Build 1484137595:	0.006%
Covered Lines:	49969
Relevant Lines:	60521

💛 - Coveralls

1ucian0 · 2022-02-15T12:48:07Z

Is there any reason for creating MeasurePauli instead of extending Measure with a basis parameter?

yaelbh · 2022-02-15T13:56:54Z

Is there any reason for creating MeasurePauli instead of extending Measure with a basis parameter?

@1ucian0 I'm not sure, but to get the answer it's important to emphasize:

MeasurePauli can have multiple qubits, whereas Measure takes only one qubit. Therefore doing something like this would also mean extension of Measure to any number of qubits.
Eventually, the goal of this PR is that for a simulator backend the transpiler will leave the instruction as-is, and will not convert it to a sequence of single-qubit measurements in the standard basis. We want to exploit the fact that multi-qubit Pauli measurement can be simulated more efficiently.

nkanazawa1989 · 2022-02-18T00:51:54Z

I found this PR is very helpful to cleanly write many calibration sequences in the experiments. I think now post rotations are okey since most backends support gate after measurement.

yaelbh · 2022-02-18T10:16:08Z

I'd like to draw the attention of the reviewers to my comments #5311 (comment).

1ucian0 · 2022-02-19T20:57:21Z

Is there any reason for creating MeasurePauli instead of extending Measure with a basis parameter?

Actually, this is a a bad idea. Each basis is, in essence, a different instructions with different decompositions and backends (such as IBM Quantum provider) and plugins (such as QASM2) might support a subset of them. Taking this suggestion back.

1ucian0 · 2022-02-19T21:15:00Z

qiskit/circuit/measure.py

@@ -36,3 +39,62 @@ def broadcast_arguments(self, qargs, cargs):
                yield qarg, [each_carg]
        else:
            raise CircuitError("register size error")
+
+
+class MeasurePauli(Measure):


See https://github.com/Qiskit/qiskit-terra/pull/5311/files#r810538319

Suggested change

class MeasurePauli(Measure):

class MeasurePauli(Instruction):

Strong +1. MeasurePauli should not be a subclass of Measure.

1ucian0 · 2022-02-19T21:15:44Z

qiskit/circuit/measure.py

-Quantum measurement in the computational basis.
+Quantum measurement


I would leave this file as it is and move measure_pauli to its own file.

1ucian0 · 2022-02-19T21:37:42Z

qiskit/visualization/matplotlib.py

+                if isinstance(op, (Measure, MeasurePauli)):
+                    if isinstance(op, Measure):
+                        basis = "Z"
+                    else:
+                        basis = op.params
+                    self._measure(node, basis=basis)


This is an example of a bug mentioned in https://github.com/Qiskit/qiskit-terra/pull/5311/files#r810538319 (it always get basis = "Z" and the basis = op.params branch is never taken).

A possible work around for this case might look something like this:

Suggested change

if isinstance(op, (Measure, MeasurePauli)):

if isinstance(op, Measure):

basis = "Z"

else:

basis = op.params

self._measure(node, basis=basis)

if isinstance(op, MeasurePauli):

self._measure(node, basis=''.join(op.params))

elif isinstance(op, Measure):

self._measure(node, basis='Z')

1ucian0 · 2022-02-19T21:47:23Z

qiskit/visualization/text.py

+        if isinstance(op, (Measure, MeasurePauli)):
+            if isinstance(op, Measure):
+                gate = MeasureFrom()
+            else:
+                basis = op.params.upper()
+                gate = MeasureFrom(basis)


This seems like a very similar situation than here: https://github.com/Qiskit/qiskit-terra/pull/5311/files#r810540202

yeap.. same situation (this might need a test)

circuit = QuantumCircuit(6, 6) circuit.measure_pauli("x", [0], [0]) circuit.barrier() circuit.measure_pauli("y", [1], [1]) circuit.barrier() circuit.measure_pauli("z", [2], [2]) circuit.barrier() circuit.measure_pauli("xyz", [3, 4, 5], [3, 4, 5]) print(circuit)

┌─┐ ░ ░ ░ q_0: ┤M├─░─────░─────░──── └╥┘ ░ ┌─┐ ░ ░ q_1: ─╫──░─┤M├─░─────░──── ║ ░ └╥┘ ░ ┌─┐ ░ q_2: ─╫──░──╫──░─┤M├─░──── ║ ░ ║ ░ └╥┘ ░ ┌─┐ q_3: ─╫──░──╫──░──╫──░─┤M├ ║ ░ ║ ░ ║ ░ └╥┘ q_4: ─╫──░──╫──░──╫──░──╫─ ║ ░ ║ ░ ║ ░ ║ q_5: ─╫──░──╫──░──╫──░──╫─ ║ ░ ║ ░ ║ ░ ║ c: 6/═╩═════╩═════╩═════╩═ 0 1 2 3

So, same workaround?

Suggested change

if isinstance(op, (Measure, MeasurePauli)):

if isinstance(op, Measure):

gate = MeasureFrom()

else:

basis = op.params.upper()

gate = MeasureFrom(basis)

if isinstance(op, (Measure, MeasurePauli)):

if isinstance(op, MeasurePauli):

gate = MeasureFrom(''.join(op.params))

elif isinstance(op, Measure):

gate = MeasureFrom()

1ucian0 · 2022-02-19T22:04:25Z

Eventually, the goal of this PR is that for a simulator backend the transpiler will leave the instruction as-is, and will not convert it to a sequence of single-qubit measurements in the standard basis. We want to exploit the fact that multi-qubit Pauli measurement can be simulated more efficiently.

The multi-qubits feature makes this PR a bit tricky. My main red flag is that multi-qubits, in this context, implies multi-clbit
and that breaks some assumptions. For example, there is no support for drawing writing-into-multiple-clbits. This might sounds like a detail, but it might have deeper implications that are not so obvious.

Considering that and since it seems kinda trivial for a backend to detect a sequence of measures, is this feature worthy? If we are okey with removing it, then we just need to add the instructions MeasureX and MeasureY (MeasureZ could be some sort of alias of the current Measure) with their own decomposition in terms of Measure.

yaelbh · 2022-02-20T12:28:30Z

Considering that and since it seems kinda trivial for a backend to detect a sequence of measures, is this feature worthy? If we are okey with removing it, then we just need to add the instructions MeasureX and MeasureY

Sounds fine for me.
@nkanazawa1989 you've been involved
@chriseclectic this work started following a discussion with you
Do you (Chris & Naoki) agree?

nkanazawa1989 · 2022-02-21T03:27:45Z

Single qubit measure is okey with me -- as current measurement instruction does. User can write a macro for mutiqubit measure if they really want. The important point for me is pauli measure instruction will add more context to the circuit and they make the code and visualized circuit more readable.

yaelbh · 2022-02-22T11:07:24Z

As I said, I agree with the move to single-qubit. However I recommend to read a bit of discussion about it in #4024, which remained without conclusions.

What's everybody's opinion:

From user's perspective, a single instruction measure_pauli (or measure_pauli with parameters (as done in Add Pauli measurements #4024) or separate measure_x, measure_y, measure_z instructions (as suggested in Add x and y measurements #3967) ?
Same question from internal implementation perspective - a single class PauliMeasure (or MeasurePauli) with parameters or separate classes MeasureX, MeasureY (in any case they will all inherit directly from Instruction) ?

itoko · 2022-02-25T01:42:01Z

Sorry to cut in, what about an idea in the middle? That is introducing measure_pauli accepting multi-qubit pauli measurement while it internally produces single-qubit PauliMeasures for now to avoid the drawer issue for mult-clbits. The direct creation of multi-qubit pauli measurement, e.g. PauliMeasure(basis="XYZ"), should raise a "not yet allowed" error for now. In this way, once the drawer issue is fixed, we can introduce true multi-qubit pauli measurement in the future without a big change. Am I missing something?

1ucian0 · 2022-03-02T20:13:58Z

closing in favor of #7716

itoko · 2022-03-03T00:09:13Z

I thought some qiskit-application developers may want a general PauliMeasure interface (but I myself had no concrete use case), while there is a clear need for single-qubit Measures from qiskit-experiments. So it makes sense to introduce single-qubit Measures at this moment. Provided we introduce single-qubit Measures, I think we should not introduce measure_pauli now (it should be added only in the case we introduce PauliMeasure in future)

joon-huh · 2022-03-30T19:20:59Z

I thought some qiskit-application developers may want a general PauliMeasure interface (but I myself had no concrete use case), while there is a clear need for single-qubit Measures from qiskit-experiments. So it makes sense to introduce single-qubit Measures at this moment. Provided we introduce single-qubit Measures, I think we should not introduce measure_pauli now (it should be added only in the case we introduce PauliMeasure in future)

Multi-qubit Pauli measurements are essential for lattice surgery fault-tolerant QC (for example https://arxiv.org/pdf/1808.02892). While it is not relevant for current hardwares, Qiskit supporting multi-qubit Pauli measurements would be nice for those who are interested in making a compiler for FTQC. I hope this feature is integrated into Qiskit soon.
-A random person.

quantumjim and others added 30 commits March 25, 2020 11:48

add initial attempt at measurements

d82d83c

Merge pull request #1 from quantumjim/quantumjim-patch-1

da54a10

add initial attempt at measurements

make x and y measurements work

8cb8e7a

implement BasisTransformationMeasurement

a86e538

Merge pull request #2 from Cryoris/generalized-measurement

9bf7a85

implement BasisTransformationMeasurement

move to PauliMeasure, inherit from Measure

3c7ed38

fix measure_z -> measure

7f86aa1

wrap z measure as well for safety

9cafdfc

its probably safer to wrap the Measure instruction if the basis is Z instead of the PauliMeasure to mimic the Measure instruction. Otherwise we might run into unforeseen issues since Measure might be used as primitive somewhere down in Terra

Merge pull request #3 from Cryoris/generalized-measurement

7caa860

Move to PauliMeasure

Merge branch 'master' into master

e3576b3

Merge branch 'master' into generalized-measurement

4ab06b7

implement chris' suggestions

1689c29

* use clifford gates only * apply inverse post rotations for correct statevector simulations * make basis argument required * change to uppercase labels (but support lowercase still)

remove unused import

80d78aa

more efficient pre/post rotation

6d46013

add comments on post rotation

e2cecac

add multi-measure capability

dcbaecf

Merge branch 'master' into generalized-measurement

7cbc815

Merge pull request #4 from Cryoris/generalized-measurement

c8bb9b8

Apply Chris' suggestions

Merge branch 'master' into master

c1584ce

Merge branch 'master' into master

bfe68a9

fix post-rotation

61ce727

Merge branch 'master' into master

3c9609e

rename PauliMeasure to MeasurePauli

d42ba56

Merge branch 'master' into master

02a38ec

Merge branch 'master' into master

5cde967

Merge branch 'master' of github.com:quantumjim/qiskit-terra into paul…

712fcc0

…i-measure

add visualization for single measurement

7c5ace0

add tests on circuit

2b8afc3

add MPL drawing

ead9d5a

fix deprecated import

97aa500

yaelbh added 4 commits October 3, 2021 12:32

black

35675d6

fix to a valid color style

4c02392

lint disable cyclic import

e7a2449

black

9e75ab4

1ucian0 added this to the 0.20 milestone Nov 22, 2021

Merge branch 'main' into meas_pauli

f12f97b

1ucian0 self-assigned this Nov 25, 2021

Nisha-Banerjee mentioned this pull request Dec 14, 2021

Add x and y measurements #3967

Open

1ucian0 reviewed Feb 19, 2022

View reviewed changes

yaelbh mentioned this pull request Feb 28, 2022

Pauli-X measurement instruction #7716

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1ucian0 closed this Mar 2, 2022

yaelbh mentioned this pull request Dec 11, 2022

Pauli X, Y, Z measurement instructions #9269

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Pauli measurement #5311

Pauli measurement #5311

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	class MeasurePauli(Measure):
	class MeasurePauli(Instruction):

		Quantum measurement in the computational basis.
		Quantum measurement

Pauli measurement #5311

Pauli measurement #5311

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