Combine 2q parallel XEB into two methods, one for benchemarking and t…

…he other for visualization (#6443)
quantumlib · Feb 8, 2024 · 34a8e59 · 34a8e59
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diff --git a/cirq-core/cirq/experiments/__init__.py b/cirq-core/cirq/experiments/__init__.py
@@ -64,3 +64,5 @@
 from cirq.experiments.t2_decay_experiment import t2_decay, T2DecayResult
 
 from cirq.experiments.xeb_fitting import XEBPhasedFSimCharacterizationOptions
+
+from cirq.experiments.two_qubit_xeb import TwoQubitXEBResult, parallel_two_qubit_xeb
diff --git a/cirq-core/cirq/experiments/two_qubit_xeb.py b/cirq-core/cirq/experiments/two_qubit_xeb.py
@@ -0,0 +1,224 @@
+# Copyright 2024 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from typing import Sequence, TYPE_CHECKING, Optional, Tuple, Dict
+
+from dataclasses import dataclass
+import itertools
+import functools
+
+from matplotlib import pyplot as plt
+import networkx as nx
+import numpy as np
+import pandas as pd
+
+from cirq import ops, devices, value, vis
+from cirq.experiments.xeb_sampling import sample_2q_xeb_circuits
+from cirq.experiments.xeb_fitting import benchmark_2q_xeb_fidelities
+from cirq.experiments.xeb_fitting import fit_exponential_decays, exponential_decay
+from cirq.experiments import random_quantum_circuit_generation as rqcg
+
+if TYPE_CHECKING:
+    import cirq
+
+
+def _grid_qubits_for_sampler(sampler: 'cirq.Sampler'):
+    if hasattr(sampler, 'processor'):
+        device = sampler.processor.get_device()
+        return sorted(device.metadata.qubit_set)
+    else:
+        qubits = devices.GridQubit.rect(3, 2, 4, 3)
+        # Delete one qubit from the rectangular arangement to
+        # 1) make it irregular 2) simplify simulation.
+        return qubits[:-1]
+
+
+def _manhattan_distance(qubit1: 'cirq.GridQubit', qubit2: 'cirq.GridQubit') -> int:
+    return abs(qubit1.row - qubit2.row) + abs(qubit1.col - qubit2.col)
+
+
+@dataclass(frozen=True)
+class TwoQubitXEBResult:
+    """Results from an XEB experiment."""
+
+    fidelities: pd.DataFrame
+
+    @functools.cached_property
+    def _qubit_pair_map(self) -> Dict[Tuple['cirq.GridQubit', 'cirq.GridQubit'], int]:
+        return {
+            (min(q0, q1), max(q0, q1)): i
+            for i, (_, _, (q0, q1)) in enumerate(self.fidelities.index)
+        }
+
+    @functools.cached_property
+    def all_qubit_pairs(self) -> Tuple[Tuple['cirq.GridQubit', 'cirq.GridQubit'], ...]:
+        return tuple(sorted(self._qubit_pair_map.keys()))
+
+    def plot_heatmap(self, ax: Optional[plt.Axes] = None, **plot_kwargs) -> plt.Axes:
+        """plot the heatmap for xeb error.
+
+        Args:
+            ax: the plt.Axes to plot on. If not given, a new figure is created,
+                plotted on, and shown.
+            **plot_kwargs: Arguments to be passed to 'plt.Axes.plot'.
+        """
+        show_plot = not ax
+        if not isinstance(ax, plt.Axes):
+            fig, ax = plt.subplots(1, 1, figsize=(8, 8))
+
+        heatmap_data: Dict[Tuple['cirq.GridQubit', ...], float] = {
+            pair: self.xeb_error(*pair) for pair in self.all_qubit_pairs
+        }
+
+        ax.set_title('device xeb error heatmap')
+
+        vis.TwoQubitInteractionHeatmap(heatmap_data).plot(ax=ax, **plot_kwargs)
+        if show_plot:
+            fig.show()
+        return ax
+
+    def plot_fitted_exponential(
+        self,
+        q0: 'cirq.GridQubit',
+        q1: 'cirq.GridQubit',
+        ax: Optional[plt.Axes] = None,
+        **plot_kwargs,
+    ) -> plt.Axes:
+        """plot the fitted model to for xeb error of a qubit pair.
+
+        Args:
+            q0: first qubit.
+            q1: second qubit.
+            ax: the plt.Axes to plot on. If not given, a new figure is created,
+                plotted on, and shown.
+            **plot_kwargs: Arguments to be passed to 'plt.Axes.plot'.
+        """
+        show_plot = not ax
+        if not isinstance(ax, plt.Axes):
+            fig, ax = plt.subplots(1, 1, figsize=(8, 8))
+
+        record = self._record(q0, q1)
+
+        ax.axhline(1, color='grey', ls='--')
+        ax.plot(record['cycle_depths'], record['fidelities'], 'o')
+        depths = np.linspace(0, np.max(record['cycle_depths']))
+        ax.plot(
+            depths,
+            exponential_decay(depths, a=record['a'], layer_fid=record['layer_fid']),
+            label='estimated exponential decay',
+            **plot_kwargs,
+        )
+        ax.set_title(f'{q0}-{q1}')
+        ax.set_ylabel('Circuit fidelity')
+        ax.set_xlabel('Cycle Depth $d$')
+        ax.legend(loc='best')
+        if show_plot:
+            fig.show()
+        return ax
+
+    def _record(self, q0, q1) -> pd.Series:
+        if q0 > q1:
+            q0, q1 = q1, q0
+        return self.fidelities.iloc[self._qubit_pair_map[(q0, q1)]]
+
+    def xeb_error(self, q0: 'cirq.GridQubit', q1: 'cirq.GridQubit') -> float:
+        """Return the XEB error of a qubit pair."""
+        p = self._record(q0, q1).layer_fid
+        return 1 - p
+
+    def all_errors(self) -> Dict[Tuple['cirq.GridQubit', 'cirq.GridQubit'], float]:
+        """Return the XEB error of all qubit pairs."""
+        return {(q0, q1): self.xeb_error(q0, q1) for q0, q1 in self.all_qubit_pairs}
+
+    def plot_histogram(self, ax: Optional[plt.Axes] = None, **plot_kwargs) -> plt.Axes:
+        """plot a histogram of all xeb errors
+
+        Args:
+            ax: the plt.Axes to plot on. If not given, a new figure is created,
+                plotted on, and shown.
+            **plot_kwargs: Arguments to be passed to 'plt.Axes.plot'.
+        """
+        fig = None
+        if ax is None:
+            fig, ax = plt.subplots(1, 1, figsize=(8, 8))
+        vis.integrated_histogram(data=self.all_errors(), ax=ax, **plot_kwargs)
+        if fig is not None:
+            fig.show(**plot_kwargs)
+        return ax
+
+
+def parallel_two_qubit_xeb(
+    sampler: 'cirq.Sampler',
+    entangling_gate: 'cirq.Gate' = ops.CZ,
+    n_repetitions: int = 10**4,
+    n_combinations: int = 10,
+    n_circuits: int = 20,
+    cycle_depths: Sequence[int] = tuple(np.arange(3, 100, 20)),
+    random_state: 'cirq.RANDOM_STATE_OR_SEED_LIKE' = 42,
+    ax: Optional[plt.Axes] = None,
+    **plot_kwargs,
+) -> TwoQubitXEBResult:
+    """A convenience method that runs the full XEB workflow.
+
+    Args:
+        sampler: The quantum engine or simulator to run the circuits.
+        entangling_gate: The entangling gate to use.
+        n_repetitions: The number of repetitions to use.
+        n_combinations: The number of combinations to generate.
+        n_circuits: The number of circuits to generate.
+        cycle_depths: The cycle depths to use.
+        random_state: The random state to use.
+        ax: the plt.Axes to plot the device layout on. If not given,
+            no plot is created.
+        **plot_kwargs: Arguments to be passed to 'plt.Axes.plot'.
+
+    Returns:
+        A TwoQubitXEBResult object representing the results of the experiment.
+    """
+    rs = value.parse_random_state(random_state)
+
+    qubits = _grid_qubits_for_sampler(sampler)
+    graph = nx.Graph(
+        pair for pair in itertools.combinations(qubits, 2) if _manhattan_distance(*pair) == 1
+    )
+
+    if ax is not None:
+        nx.draw_networkx(graph, pos={q: (q.row, q.col) for q in qubits}, ax=ax)
+        ax.set_title('device layout')
+        ax.plot(**plot_kwargs)
+
+    circuit_library = rqcg.generate_library_of_2q_circuits(
+        n_library_circuits=n_circuits, two_qubit_gate=entangling_gate, random_state=rs
+    )
+
+    combs_by_layer = rqcg.get_random_combinations_for_device(
+        n_library_circuits=len(circuit_library),
+        n_combinations=n_combinations,
+        device_graph=graph,
+        random_state=rs,
+    )
+
+    sampled_df = sample_2q_xeb_circuits(
+        sampler=sampler,
+        circuits=circuit_library,
+        cycle_depths=cycle_depths,
+        combinations_by_layer=combs_by_layer,
+        shuffle=rs,
+        repetitions=n_repetitions,
+    )
+
+    fids = benchmark_2q_xeb_fidelities(
+        sampled_df=sampled_df, circuits=circuit_library, cycle_depths=cycle_depths
+    )
+
+    return TwoQubitXEBResult(fit_exponential_decays(fids))
diff --git a/cirq-core/cirq/experiments/two_qubit_xeb_test.py b/cirq-core/cirq/experiments/two_qubit_xeb_test.py
@@ -0,0 +1,100 @@
+# Copyright 2024 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Wraps Parallel Two Qubit XEB into a few convenience methods."""
+from contextlib import redirect_stdout, redirect_stderr
+import itertools
+import io
+import random
+
+import matplotlib.pyplot as plt
+
+import numpy as np
+import networkx as nx
+import pytest
+
+import cirq
+
+
+def _manhattan_distance(qubit1: 'cirq.GridQubit', qubit2: 'cirq.GridQubit') -> int:
+    return abs(qubit1.row - qubit2.row) + abs(qubit1.col - qubit2.col)
+
+
+class MockDevice(cirq.Device):
+    @property
+    def metadata(self):
+        qubits = cirq.GridQubit.rect(3, 2, 4, 3)
+        graph = nx.Graph(
+            pair for pair in itertools.combinations(qubits, 2) if _manhattan_distance(*pair) == 1
+        )
+        return cirq.DeviceMetadata(qubits, graph)
+
+
+class MockProcessor:
+    def get_device(self):
+        return MockDevice()
+
+
+class DensityMatrixSimulatorWithProcessor(cirq.DensityMatrixSimulator):
+    @property
+    def processor(self):
+        return MockProcessor()
+
+
+@pytest.mark.parametrize(
+    'sampler',
+    [
+        cirq.DensityMatrixSimulator(
+            seed=0, noise=cirq.ConstantQubitNoiseModel(cirq.amplitude_damp(0.1))
+        ),
+        DensityMatrixSimulatorWithProcessor(
+            seed=0, noise=cirq.ConstantQubitNoiseModel(cirq.amplitude_damp(0.1))
+        ),
+    ],
+)
+def test_parallel_two_qubit_xeb(sampler: cirq.Sampler):
+    np.random.seed(0)
+    random.seed(0)
+
+    with redirect_stdout(io.StringIO()), redirect_stderr(io.StringIO()):
+        res = cirq.experiments.parallel_two_qubit_xeb(
+            sampler=sampler,
+            n_repetitions=100,
+            n_combinations=1,
+            n_circuits=1,
+            cycle_depths=[3, 4, 5],
+            random_state=0,
+        )
+
+        got = [res.xeb_error(*reversed(pair)) for pair in res.all_qubit_pairs]
+        np.testing.assert_allclose(got, 0.1, atol=1e-1)
+
+
+@pytest.mark.usefixtures('closefigures')
+@pytest.mark.parametrize(
+    'sampler', [cirq.DensityMatrixSimulator(seed=0), DensityMatrixSimulatorWithProcessor(seed=0)]
+)
+@pytest.mark.parametrize('ax', [None, plt.subplots(1, 1, figsize=(8, 8))[1]])
+def test_plotting(sampler, ax):
+    res = cirq.experiments.parallel_two_qubit_xeb(
+        sampler=sampler,
+        n_repetitions=1,
+        n_combinations=1,
+        n_circuits=1,
+        cycle_depths=[3, 4, 5],
+        random_state=0,
+        ax=ax,
+    )
+    res.plot_heatmap(ax=ax)
+    res.plot_fitted_exponential(cirq.GridQubit(4, 4), cirq.GridQubit(4, 3), ax=ax)
+    res.plot_histogram(ax=ax)
Original file line number	Diff line number	Diff line change
Expand Up		@@ -64,3 +64,5 @@
		from cirq.experiments.t2_decay_experiment import t2_decay, T2DecayResult

		from cirq.experiments.xeb_fitting import XEBPhasedFSimCharacterizationOptions

		from cirq.experiments.two_qubit_xeb import TwoQubitXEBResult, parallel_two_qubit_xeb