Merge branch 'main' into move-target

CITATION.bib

@@ -1,6 +1,9 @@
-@misc{Qiskit,
-    author = {{Qiskit contributors}},
-    title = {Qiskit: An Open-source Framework for Quantum Computing},
-    year = {2023},
-    doi = {10.5281/zenodo.2573505}
+@misc{qiskit2024,
+      title={Quantum computing with {Q}iskit},
+      author={Javadi-Abhari, Ali and Treinish, Matthew and Krsulich, Kevin and Wood, Christopher J. and Lishman, Jake and Gacon, Julien and Martiel, Simon and Nation, Paul D. and Bishop, Lev S. and Cross, Andrew W. and Johnson, Blake R. and Gambetta, Jay M.},
+      year={2024},
+      doi={10.48550/arXiv.2405.08810},
+      eprint={2405.08810},
+      archivePrefix={arXiv},
+      primaryClass={quant-ph}
 }

crates/accelerate/Cargo.toml

@@ -21,7 +21,7 @@ num-complex = "0.4"
 num-bigint = "0.4"
 rustworkx-core = "0.14"
 faer = "0.18.2"
-itertools = "0.12.1"
+itertools = "0.13.0"
 qiskit-circuit.workspace = true
 
 [dependencies.smallvec]

crates/accelerate/src/dense_layout.rs

@@ -15,8 +15,8 @@ use ahash::RandomState;
 use hashbrown::{HashMap, HashSet};
 use indexmap::IndexSet;
 use ndarray::prelude::*;
+use numpy::IntoPyArray;
 use numpy::PyReadonlyArray2;
-use numpy::ToPyArray;
 use rayon::prelude::*;
 
 use pyo3::prelude::*;
@@ -108,10 +108,35 @@ pub fn best_subset(
     use_error: bool,
     symmetric_coupling_map: bool,
     error_matrix: PyReadonlyArray2<f64>,
-) -> PyResult<(PyObject, PyObject, PyObject)> {
+) -> (PyObject, PyObject, PyObject) {
     let coupling_adj_mat = coupling_adjacency.as_array();
-    let coupling_shape = coupling_adj_mat.shape();
     let err = error_matrix.as_array();
+    let [rows, cols, best_map] = best_subset_inner(
+        num_qubits,
+        coupling_adj_mat,
+        num_meas,
+        num_cx,
+        use_error,
+        symmetric_coupling_map,
+        err,
+    );
+    (
+        rows.into_pyarray_bound(py).into(),
+        cols.into_pyarray_bound(py).into(),
+        best_map.into_pyarray_bound(py).into(),
+    )
+}
+
+pub fn best_subset_inner(
+    num_qubits: usize,
+    coupling_adj_mat: ArrayView2<f64>,
+    num_meas: usize,
+    num_cx: usize,
+    use_error: bool,
+    symmetric_coupling_map: bool,
+    err: ArrayView2<f64>,
+) -> [Vec<usize>; 3] {
+    let coupling_shape = coupling_adj_mat.shape();
     let avg_meas_err = err.diag().mean().unwrap();
 
     let map_fn = |k| -> SubsetResult {
@@ -216,11 +241,7 @@ pub fn best_subset(
     let rows: Vec<usize> = new_cmap.iter().map(|edge| edge[0]).collect();
     let cols: Vec<usize> = new_cmap.iter().map(|edge| edge[1]).collect();
 
-    Ok((
-        rows.to_pyarray_bound(py).into(),
-        cols.to_pyarray_bound(py).into(),
-        best_map.to_pyarray_bound(py).into(),
-    ))
+    [rows, cols, best_map]
 }
 
 #[pymodule]

crates/accelerate/src/sabre/layout.rs

@@ -15,6 +15,7 @@ use pyo3::prelude::*;
 use pyo3::Python;
 
 use hashbrown::HashSet;
+use ndarray::prelude::*;
 use numpy::{IntoPyArray, PyArray, PyReadonlyArray2};
 use rand::prelude::*;
 use rand_pcg::Pcg64Mcg;
@@ -29,6 +30,8 @@ use super::sabre_dag::SabreDAG;
 use super::swap_map::SwapMap;
 use super::{Heuristic, NodeBlockResults, SabreResult};
 
+use crate::dense_layout::best_subset_inner;
+
 #[pyfunction]
 #[pyo3(signature = (dag, neighbor_table, distance_matrix, heuristic, max_iterations, num_swap_trials, num_random_trials, seed=None, partial_layouts=vec![]))]
 pub fn sabre_layout_and_routing(
@@ -52,6 +55,12 @@ pub fn sabre_layout_and_routing(
     let mut starting_layouts: Vec<Vec<Option<u32>>> =
         (0..num_random_trials).map(|_| vec![]).collect();
     starting_layouts.append(&mut partial_layouts);
+    // Run a dense layout trial
+    starting_layouts.push(compute_dense_starting_layout(
+        dag.num_qubits,
+        &target,
+        run_in_parallel,
+    ));
     let outer_rng = match seed {
         Some(seed) => Pcg64Mcg::seed_from_u64(seed),
         None => Pcg64Mcg::from_entropy(),
@@ -208,3 +217,26 @@ fn layout_trial(
         .collect();
     (initial_layout, final_permutation, sabre_result)
 }
+
+fn compute_dense_starting_layout(
+    num_qubits: usize,
+    target: &RoutingTargetView,
+    run_in_parallel: bool,
+) -> Vec<Option<u32>> {
+    let mut adj_matrix = target.distance.to_owned();
+    if run_in_parallel {
+        adj_matrix.par_mapv_inplace(|x| if x == 1. { 1. } else { 0. });
+    } else {
+        adj_matrix.mapv_inplace(|x| if x == 1. { 1. } else { 0. });
+    }
+    let [_rows, _cols, map] = best_subset_inner(
+        num_qubits,
+        adj_matrix.view(),
+        0,
+        0,
+        false,
+        true,
+        aview2(&[[0.]]),
+    );
+    map.into_iter().map(|x| Some(x as u32)).collect()
+}