Fix QuantumCircuit.depth with zero-operands and Expr nodes
#12429
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This causes `QuantumCircuit.depth` to correctly handle cases where a circuit instruction has zero operands (such as `GlobalPhaseGate`), and to treat classical bits and real-time variables used inside `Expr` conditions as part of the depth calculations. This is in line with `DAGCircuit`. This commit still does not add the same `recurse` argument from `DAGCircuit.depth`, because the arguments for not adding it to `QuantumCircuit.depth` at the time still hold; there is no clear meaning to it for general control flow from a user's perspective, and it was only added to the `DAGCircuit` methods because there it is more of a proxy for optimising over all possible inner blocks.
jakelishman
added
stable backport potential
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Pull Request Test Coverage Report for Build 9128390726Details
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ElePT
reviewed
Jun 7, 2024
| @@ -3307,6 +3307,9 @@ def depth( | |||
| ) -> int: | |||
| """Return circuit depth (i.e., length of critical path). | |||
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| .. warning:: | |||
| This operation is not well defined if the circuit contains control-flow operations. | |||
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would it make sense to add more info in this warning? would it be inaccurate to say, for example:
Suggested change
| This operation is not well defined if the circuit contains control-flow operations. | |
| This operation is not well defined if the circuit contains control-flow operations, but | |
| their variables and clbits are counted in the depth calculation. | |
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I was mostly deliberately trying to avoid saying anything about what happens in the return value of this if there's control-flow operations, since the whole result is ill defined. I didn't want to commit to anything one way or the other.
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I suspected that was the case, and I think that makes sense too.
ElePT
approved these changes
Jun 7, 2024
| @@ -3307,6 +3307,9 @@ def depth( | |||
| ) -> int: | |||
| """Return circuit depth (i.e., length of critical path). | |||
|
|
|||
| .. warning:: | |||
| This operation is not well defined if the circuit contains control-flow operations. | |||
There was a problem hiding this comment.
I suspected that was the case, and I think that makes sense too.
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This causes `QuantumCircuit.depth` to correctly handle cases where a circuit instruction has zero operands (such as `GlobalPhaseGate`), and to treat classical bits and real-time variables used inside `Expr` conditions as part of the depth calculations. This is in line with `DAGCircuit`. This commit still does not add the same `recurse` argument from `DAGCircuit.depth`, because the arguments for not adding it to `QuantumCircuit.depth` at the time still hold; there is no clear meaning to it for general control flow from a user's perspective, and it was only added to the `DAGCircuit` methods because there it is more of a proxy for optimising over all possible inner blocks. (cherry picked from commit d18a74c)
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… (#12528) This causes `QuantumCircuit.depth` to correctly handle cases where a circuit instruction has zero operands (such as `GlobalPhaseGate`), and to treat classical bits and real-time variables used inside `Expr` conditions as part of the depth calculations. This is in line with `DAGCircuit`. This commit still does not add the same `recurse` argument from `DAGCircuit.depth`, because the arguments for not adding it to `QuantumCircuit.depth` at the time still hold; there is no clear meaning to it for general control flow from a user's perspective, and it was only added to the `DAGCircuit` methods because there it is more of a proxy for optimising over all possible inner blocks. (cherry picked from commit d18a74c) Co-authored-by: Jake Lishman <jake.lishman@ibm.com>
Procatv
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Aug 1, 2024
…t#12429) This causes `QuantumCircuit.depth` to correctly handle cases where a circuit instruction has zero operands (such as `GlobalPhaseGate`), and to treat classical bits and real-time variables used inside `Expr` conditions as part of the depth calculations. This is in line with `DAGCircuit`. This commit still does not add the same `recurse` argument from `DAGCircuit.depth`, because the arguments for not adding it to `QuantumCircuit.depth` at the time still hold; there is no clear meaning to it for general control flow from a user's perspective, and it was only added to the `DAGCircuit` methods because there it is more of a proxy for optimising over all possible inner blocks.
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Summary
This causes
QuantumCircuit.depthto correctly handle cases where a circuit instruction has zero operands (such asGlobalPhaseGate), and to treat classical bits and real-time variables used insideExprconditions as part of the depth calculations. This is in line withDAGCircuit.This commit still does not add the same
recurseargument fromDAGCircuit.depth, because the arguments for not adding it toQuantumCircuit.depthat the time still hold; there is no clear meaning to it for general control flow from a user's perspective, and it was only added to theDAGCircuitmethods because there it is more of a proxy for optimising over all possible inner blocks.Details and comments
Fix #12426.