---
title: LightCone (v2.0)
description: API reference for qiskit.transpiler.passes.LightCone in qiskit v2.0
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/2.0/qiskit.transpiler.passes.LightCone
---

# LightCone

*class* `qiskit.transpiler.passes.LightCone(*args, **kwargs)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/transpiler/passes/optimization/light_cone.py#L26-L135)

Bases: [`TransformationPass`](/docs/api/qiskit/2.0/qiskit.transpiler.TransformationPass "qiskit.transpiler.basepasses.TransformationPass")

Remove the gates that do not affect the outcome of a measurement on a circuit.

Pass for computing the light-cone of an observable or measurement. The Pass can handle either an observable one would like to measure or a measurement on a set of qubits.

**Parameters**

- **bit\_terms** – If `None` the light-cone will be computed for the set of measurements in the circuit. If a string is specified, the light-cone will correspond to the reduced circuit with the same expectation value for the observable.
- **indices** – list of non-trivial indices corresponding to the observable in `bit_terms`.

## Attributes

### is\_analysis\_pass

Check if the pass is an analysis pass.

If the pass is an AnalysisPass, that means that the pass can analyze the DAG and write the results of that analysis in the property set. Modifications on the DAG are not allowed by this kind of pass.

### is\_transformation\_pass

Check if the pass is a transformation pass.

If the pass is a TransformationPass, that means that the pass can manipulate the DAG, but cannot modify the property set (but it can be read).

## Methods

### execute

`execute(passmanager_ir, state, callback=None)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/transpiler/basepasses.py#L161-L180)

Execute optimization task for input Qiskit IR.

**Parameters**

- **passmanager\_ir** ([*Any*](https://docs.python.org/3/library/typing.html#typing.Any)) – Qiskit IR to optimize.
- **state** ([*PassManagerState*](/docs/api/qiskit/2.0/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")) – State associated with workflow execution by the pass manager itself.
- **callback** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable) *| None*) – A callback function which is caller per execution of optimization task.

**Returns**

Optimized Qiskit IR and state of the workflow.

**Return type**

[tuple](https://docs.python.org/3/library/stdtypes.html#tuple)\[[*Any*](https://docs.python.org/3/library/typing.html#typing.Any), [qiskit.passmanager.compilation\_status.PassManagerState](/docs/api/qiskit/2.0/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")]

### name

`name()`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/passmanager/base_tasks.py#L68-L70)

Name of the pass.

**Return type**

[str](https://docs.python.org/3/library/stdtypes.html#str)

### run

`run(dag)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/transpiler/passes/optimization/light_cone.py#L90-L135)

Run the LightCone pass on dag.

**Parameters**

**dag** ([*DAGCircuit*](/docs/api/qiskit/2.0/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit")) – The DAG to reduce.

**Returns**

The DAG reduced to the light-cone of the observable.

**Return type**

[*DAGCircuit*](/docs/api/qiskit/2.0/qiskit.dagcircuit.DAGCircuit "qiskit._accelerate.circuit.DAGCircuit")

### update\_status

`update_status(state, run_state)`

[GitHub](https://github.com/Qiskit/qiskit/tree/stable/2.0/qiskit/transpiler/basepasses.py#L182-L190)

Update workflow status.

**Parameters**

- **state** ([*PassManagerState*](/docs/api/qiskit/2.0/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")) – Pass manager state to update.
- **run\_state** (*RunState*) – Completion status of current task.

**Returns**

Updated pass manager state.

**Return type**

[*PassManagerState*](/docs/api/qiskit/2.0/qiskit.passmanager.PassManagerState "qiskit.passmanager.compilation_status.PassManagerState")