Add method to compute estimated duration of scheduled circuit (backport #13783)

crates/accelerate/src/circuit_duration.rs

@@ -0,0 +1,112 @@
+// This code is part of Qiskit.
+//
+// (C) Copyright IBM 2025
+//
+// This code is licensed under the Apache License, Version 2.0. You may
+// obtain a copy of this license in the LICENSE.txt file in the root directory
+// of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+//
+// Any modifications or derivative works of this code must retain this
+// copyright notice, and modified files need to carry a notice indicating
+// that they have been altered from the originals.
+
+use pyo3::intern;
+use pyo3::prelude::*;
+use pyo3::wrap_pyfunction;
+
+use qiskit_circuit::dag_circuit::{DAGCircuit, NodeType, Wire};
+use qiskit_circuit::operations::{Operation, OperationRef, Param};
+
+use crate::nlayout::PhysicalQubit;
+use crate::target_transpiler::Target;
+use crate::QiskitError;
+use rustworkx_core::dag_algo::longest_path;
+use rustworkx_core::petgraph::stable_graph::StableDiGraph;
+use rustworkx_core::petgraph::visit::{EdgeRef, IntoEdgeReferences};
+
+/// Estimate the duration of a scheduled circuit in seconds
+#[pyfunction]
+pub(crate) fn compute_estimated_duration(dag: &DAGCircuit, target: &Target) -> PyResult<f64> {
+    let dt = target.dt;
+
+    let get_duration =
+        |edge: <&StableDiGraph<NodeType, Wire> as IntoEdgeReferences>::EdgeRef| -> PyResult<f64> {
+            let node_weight = &dag.dag()[edge.target()];
+            match node_weight {
+                NodeType::Operation(inst) => {
+                    let name = inst.op.name();
+                    let qubits = dag.get_qargs(inst.qubits);
+                    let physical_qubits: Vec<PhysicalQubit> =
+                        qubits.iter().map(|x| PhysicalQubit::new(x.0)).collect();
+
+                    if name == "delay" {
+                        let dur = &inst.params.as_ref().unwrap()[0];
+                        let OperationRef::Instruction(op) = inst.op.view() else {
+                            unreachable!("Invalid type for delay instruction");
+                        };
+                        Python::with_gil(|py| {
+                            let unit: String = op
+                                .instruction
+                                .getattr(py, intern!(py, "unit"))?
+                                .extract(py)?;
+                            if unit == "dt" {
+                                if let Some(dt) = dt {
+                                    match dur {
+                                    Param::Float(val) => Ok(val * dt),
+                                    Param::Obj(val) => {
+                                        let dur_float: f64 = val.extract(py)?;
+                                        Ok(dur_float * dt)
+                                    },
+                                    Param::ParameterExpression(_) => Err(QiskitError::new_err(
+                                        "Circuit contains parameterized delays, can't compute a duration estimate with this circuit"
+                                    )),
+                                }
+                                } else {
+                                    Err(QiskitError::new_err(
+                                        "Circuit contains delays in dt but the target doesn't specify dt"
+                                    ))
+                                }
+                            } else if unit == "s" {
+                                match dur {
+                                    Param::Float(val) => Ok(*val),
+                                    _ => Err(QiskitError::new_err(
+                                        "Invalid type for parameter value for delay in circuit",
+                                    )),
+                                }
+                            } else {
+                                Err(QiskitError::new_err(
+                                    "Circuit contains delays in units other then seconds or dt, the circuit is not scheduled."
+                                ))
+                            }
+                        })
+                    } else if name == "barrier" {
+                        Ok(0.)
+                    } else {
+                        match target.get_duration(name, &physical_qubits) {
+                            Some(dur) => Ok(dur),
+                            None => Err(QiskitError::new_err(format!(
+                                "Duration not found for {} on qubits: {:?}",
+                                name, qubits
+                            ))),
+                        }
+                    }
+                }
+                NodeType::QubitOut(_) | NodeType::ClbitOut(_) => Ok(0.),
+                NodeType::ClbitIn(_) | NodeType::QubitIn(_) => {
+                    Err(QiskitError::new_err("Invalid circuit provided"))
+                }
+                _ => Err(QiskitError::new_err(
+                    "Circuit contains Vars, duration can't be calculated with classical variables",
+                )),
+            }
+        };
+    match longest_path(dag.dag(), get_duration)? {
+        Some((_, weight)) => Ok(weight),
+        None => Err(QiskitError::new_err("Invalid circuit provided")),
+    }
+}
+
+pub fn compute_duration(m: &Bound<PyModule>) -> PyResult<()> {
+    m.add_wrapped(wrap_pyfunction!(compute_estimated_duration))?;
+    Ok(())
+}

crates/accelerate/src/lib.rs

@@ -21,6 +21,7 @@ use pyo3::import_exception;
 pub mod barrier_before_final_measurement;
 pub mod basis;
 pub mod check_map;
+pub mod circuit_duration;
 pub mod circuit_library;
 pub mod commutation_analysis;
 pub mod commutation_cancellation;

crates/accelerate/src/target_transpiler/mod.rs

@@ -951,6 +951,17 @@ impl Target {
         })
     }
 
+    /// Get the duration of a given instruction in the target
+    pub fn get_duration(&self, name: &str, qargs: &[PhysicalQubit]) -> Option<f64> {
+        self.gate_map.get(name).and_then(|gate_props| {
+            let qargs_key: Qargs = qargs.iter().cloned().collect();
+            match gate_props.get(Some(&qargs_key)) {
+                Some(props) => props.as_ref().and_then(|inst_props| inst_props.duration),
+                None => None,
+            }
+        })
+    }
+
     /// Get an iterator over the indices of all physical qubits of the target
     pub fn physical_qubits(&self) -> impl ExactSizeIterator<Item = usize> {
         0..self.num_qubits.unwrap_or_default()

crates/pyext/src/lib.rs

@@ -31,6 +31,7 @@ fn _accelerate(m: &Bound<PyModule>) -> PyResult<()> {
     add_submodule(m, ::qiskit_accelerate::barrier_before_final_measurement::barrier_before_final_measurements_mod, "barrier_before_final_measurement")?;
     add_submodule(m, ::qiskit_accelerate::basis::basis, "basis")?;
     add_submodule(m, ::qiskit_accelerate::check_map::check_map_mod, "check_map")?;
+    add_submodule(m, ::qiskit_accelerate::circuit_duration::compute_duration, "circuit_duration")?;
     add_submodule(m, ::qiskit_accelerate::circuit_library::circuit_library, "circuit_library")?;
     add_submodule(m, ::qiskit_accelerate::commutation_analysis::commutation_analysis, "commutation_analysis")?;
     add_submodule(m, ::qiskit_accelerate::commutation_cancellation::commutation_cancellation, "commutation_cancellation")?;

qiskit/__init__.py

@@ -110,6 +110,7 @@
 sys.modules["qiskit._accelerate.twirling"] = _accelerate.twirling
 sys.modules["qiskit._accelerate.high_level_synthesis"] = _accelerate.high_level_synthesis
 sys.modules["qiskit._accelerate.remove_identity_equiv"] = _accelerate.remove_identity_equiv
+sys.modules["qiskit._accelerate.circuit_duration"] = _accelerate.circuit_duration
 
 from qiskit.exceptions import QiskitError, MissingOptionalLibraryError
 

qiskit/circuit/quantumcircuit.py

@@ -40,6 +40,7 @@
 import numpy as np
 from qiskit._accelerate.circuit import CircuitData
 from qiskit._accelerate.circuit import StandardGate
+from qiskit._accelerate.circuit_duration import compute_estimated_duration
 from qiskit.exceptions import QiskitError
 from qiskit.utils.multiprocessing import is_main_process
 from qiskit.circuit.instruction import Instruction
@@ -156,6 +157,8 @@ class QuantumCircuit:
     :attr:`data`              List of individual :class:`CircuitInstruction`\\ s that make up the
                               circuit.
     :attr:`duration`          Total duration of the circuit, added by scheduling transpiler passes.
+                              This attribute is deprecated and :meth:`.estimate_duration` should
+                              be used instead.
 
     :attr:`layout`            Hardware layout and routing information added by the transpiler.
     :attr:`num_ancillas`      The number of ancilla qubits in the circuit.
@@ -921,8 +924,9 @@ class QuantumCircuit:
 
     If a :class:`QuantumCircuit` has been scheduled as part of a transpilation pipeline, the timing
     information for individual qubits can be accessed.  The whole-circuit timing information is
-    available through the :attr:`duration`, :attr:`unit` and :attr:`op_start_times` attributes.
+    available through the :meth:`estimate_duration` method and :attr:`op_start_times` attribute.
 
+    .. automethod:: estimate_duration
     .. automethod:: qubit_duration
     .. automethod:: qubit_start_time
     .. automethod:: qubit_stop_time
@@ -6654,6 +6658,65 @@ def qubit_stop_time(self, *qubits: Union[Qubit, int]) -> float:
 
         return 0  # If there are no instructions over bits
 
+    def estimate_duration(self, target, unit: str = "s") -> int | float:
+        """Estimate the duration of a scheduled circuit
+
+        This method computes the estimate of the circuit duration by finding
+        the longest duration path in the circuit based on the durations
+        provided by a given target. This method only works for simple circuits
+        that have no control flow or other classical feed-forward operations.
+
+        Args:
+            target (Target): The :class:`.Target` instance that contains durations for
+                the instructions if the target is missing duration data for any of the
+                instructions in the circuit an :class:`.QiskitError` will be raised. This
+                should be the same target object used as the target for transpilation.
+            unit: The unit to return the duration in. This defaults to "s" for seconds
+                but this can be a supported SI prefix for seconds returns. For example
+                setting this to "n" will return in unit of nanoseconds. Supported values
+                of this type are "f", "p", "n", "u", "µ", "m", "k", "M", "G", "T", and
+                "P". Additionally, a value of "dt" is also accepted to output an integer
+                in units of "dt". For this to function "dt" must be specified in the
+                ``target``.
+
+        Returns:
+            The estimated duration for the execution of a single shot of the circuit in
+            the specified unit.
+
+        Raises:
+            QiskitError: If the circuit is not scheduled or contains other
+                details that prevent computing an estimated duration from
+                (such as parameterized delay).
+        """
+        from qiskit.converters import circuit_to_dag
+
+        dur = compute_estimated_duration(circuit_to_dag(self), target)
+        if unit == "s":
+            return dur
+        if unit == "dt":
+            from qiskit.circuit.duration import duration_in_dt  # pylint: disable=cyclic-import
+
+            return duration_in_dt(dur, target.dt)
+
+        prefix_dict = {
+            "f": 1e-15,
+            "p": 1e-12,
+            "n": 1e-9,
+            "u": 1e-6,
+            "µ": 1e-6,
+            "m": 1e-3,
+            "k": 1e3,
+            "M": 1e6,
+            "G": 1e9,
+            "T": 1e12,
+            "P": 1e15,
+        }
+        if unit not in prefix_dict:
+            raise QiskitError(
+                f"Specified unit: {unit} is not a valid/supported SI prefix, 's', or 'dt'"
+            )
+        return dur / prefix_dict[unit]
+
 
 class _OuterCircuitScopeInterface(CircuitScopeInterface):
     # This is an explicit interface-fulfilling object friend of QuantumCircuit that acts as its

releasenotes/notes/add-estimate_duration-method-a35bf8eef4b2f210.yaml

@@ -0,0 +1,7 @@
+---
+features_circuits:
+  - |
+    Added a new method, :meth:`.QuantumCircuit.estimate_duration`, to compute
+    the estimated duration of a scheduled circuit output from the :mod:`.transpiler`.
+    This should be used if you need an estimate of the full circuit duration instead
+    of the deprecated :attr:`.QuantumCircuit.duration` attribute.