Add DFL experiment code (#443)

This PR adds code for the  Disorder-Free Localization (DFL) simulation in both 1d and 2d.

This contains code to run the experiments for Figures 1 and 3 of arXiv:2410.06557.
---------

Co-authored-by: Shashwat Kumar <kshashwat@google.com>

Author: eliottrosenberg

recirq/dfl/__init__.py

@@ -0,0 +1,321 @@
+# Copyright 2025 Google
+#
+# 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.
+
+"""Generates the Trotterized circuits for 1D Disorder-Free Localization (DFL) experiments.
+"""
+
+from collections.abc import Sequence
+from typing import List
+
+import cirq
+import matplotlib.pyplot as plt
+import numpy as np
+import numpy.typing as npt
+from tqdm import tqdm
+
+#import Enums
+from recirq.dfl.dfl_enums import TwoQubitGate, InitialState, Basis
+
+def trotter_circuit(
+    grid: Sequence[cirq.GridQubit],
+    n_cycles: int,
+    dt: float,
+    h: float,
+    mu: float,
+    two_qubit_gate: TwoQubitGate = TwoQubitGate.CZ,
+) -> cirq.Circuit:
+    """Constructs a Trotter circuit for 1D Disorder-Free Localization (DFL) simulation.
+
+    Args:
+        grid: The 1D sequence of qubits used in the experiment.
+        n_cycles: The number of Trotter steps/cycles to include.
+        dt: The time step size for the Trotterization.
+        h: The gauge field strength coefficient.
+        mu: The matter field strength coefficient.
+        two_qubit_gate: The type of two-qubit gate to use in the layers.
+            Use an Enum member from TwoQubitGate (CZ or CPHASE).
+
+    Returns:
+        The complete cirq.Circuit for the Trotter evolution.
+
+    Raises:
+        ValueError: If an invalid `two_qubit_gate` option is provided.
+    """
+    if two_qubit_gate.value == TwoQubitGate.CZ.value:
+        return _layer_floquet_cz(grid, dt, h, mu) * n_cycles
+
+    elif two_qubit_gate.value == TwoQubitGate.CPHASE.value:
+        if n_cycles == 0:
+            return cirq.Circuit()
+        if n_cycles == 1:
+            return _layer_floquet_cphase_first(
+                grid, dt, h, mu
+            ) + _layer_floquet_cphase_last_missing_piece(grid, dt, h, mu)
+        else:
+            return (
+                _layer_floquet_cphase_first(grid, dt, h, mu)
+                + (n_cycles - 1) * _layer_floquet_cphase_middle(grid, dt, h, mu)
+                + _layer_floquet_cphase_last_missing_piece(grid, dt, h, mu)
+            )
+    else:
+        raise ValueError("Two-qubit gate can only be cz or cphase")
+
+
+def _layer_floquet_cz(
+    grid: Sequence[cirq.GridQubit], dt: float, h: float, mu: float
+) -> cirq.Circuit:
+    moment_rz = []
+    moment_rx = []
+    moment_h = []
+    for i in range(len(grid)):
+        q = grid[i]
+        if i % 2 == 1:
+            moment_rz.append(cirq.rz(dt).on(q))
+            moment_h.append(cirq.H(q))
+            moment_rx.append(cirq.rx(2 * h * dt).on(q))
+        else:
+            moment_rx.append(cirq.rx(2 * mu * dt).on(q))
+    return (
+        cirq.Circuit.from_moments(cirq.Moment(moment_rz))
+        + _change_basis(grid)
+        + cirq.Circuit.from_moments(cirq.Moment(moment_rx))
+        + _change_basis(grid)
+        + cirq.Circuit.from_moments(cirq.Moment(moment_rz))
+    )
+
+
+def _layer_floquet_cphase_middle(
+    grid: Sequence[cirq.GridQubit], dt: float, h: float, mu: float
+) -> cirq.Circuit:
+    n = len(grid)
+    moment_0 = []
+    moment_1 = []
+    moment_h = []
+    moment_rz = []
+    moment_rx = []
+
+    for i in range(n // 2):
+        q0 = grid[(2 * i)]
+        q = grid[2 * i + 1]
+        q1 = grid[(2 * i + 2) % n]
+        moment_0.append(cirq.CZ(q0, q))  # left to right
+        moment_1.append(cirq.cphase(-4 * dt).on(q1, q))  # right to left
+
+        moment_h.append(cirq.H(q))
+
+        moment_rz.append(cirq.rz(2 * dt).on(q))
+        moment_rz.append(cirq.rz(2 * dt).on(q1))
+
+    for i in range(n):
+        q = grid[i]
+        if i % 2 == 1:
+            moment_rx.append(cirq.rx(2 * h * dt).on(q))
+        else:
+            moment_rx.append(cirq.rx(2 * mu * dt).on(q))
+
+    moment_rz_new = []
+    qubits_covered = []
+    for gate in moment_rz:
+        count = moment_rz.count(gate)
+        qubit = gate.qubits[0]
+        if qubit not in qubits_covered:
+            moment_rz_new.append(cirq.rz(2 * count * dt).on(qubit))
+            qubits_covered.append(qubit)
+
+    return cirq.Circuit.from_moments(
+        cirq.Moment(moment_h),
+        cirq.Moment(moment_0),
+        cirq.Moment(moment_h),
+        cirq.Moment(moment_rz_new),
+        cirq.Moment(moment_1),
+        cirq.Moment(moment_h),
+        cirq.Moment(moment_0),
+        cirq.Moment(moment_h),
+        cirq.Moment(moment_rx),
+    )
+
+
+def _layer_floquet_cphase_first(
+    grid: Sequence[cirq.GridQubit], dt: float, h: float, mu: float
+) -> cirq.Circuit:
+    moment_rz = []
+    moment_rx = []
+
+    for i in range(len(grid)):
+        q = grid[i]
+        if i % 2 == 1:
+            moment_rz.append(cirq.rz(dt).on(q))
+            moment_rx.append(cirq.rx(2 * h * dt).on(q))
+        else:
+            moment_rx.append(cirq.rx(2 * mu * dt).on(q))
+
+    return (
+        cirq.Circuit.from_moments(cirq.Moment(moment_rz))
+        + _change_basis(grid)
+        + cirq.Circuit.from_moments(cirq.Moment(moment_rx))
+    )
+
+
+def _layer_floquet_cphase_last_missing_piece(
+    grid: Sequence[cirq.GridQubit], dt: float, h: float, mu: float
+) -> cirq.Circuit:
+    moment_rz = []
+    for i in range(len(grid)):
+        q = grid[i]
+        if i % 2 == 1:
+            moment_rz.append(cirq.rz(dt).on(q))
+
+    return _change_basis(grid) + cirq.Circuit.from_moments(cirq.Moment(moment_rz))
+
+
+def _layer_hadamard(grid: Sequence[cirq.GridQubit], which_qubits="all") -> cirq.Circuit:
+    moment = []
+    for i in range(len(grid)):
+        q = grid[i]
+
+        if i % 2 == 1 and (which_qubits == "gauge" or which_qubits == "all"):
+            moment.append(cirq.H(q))
+
+        elif i % 2 == 0 and (which_qubits == "matter" or which_qubits == "all"):
+            moment.append(cirq.H(q))
+    return cirq.Circuit.from_moments(cirq.Moment(moment))
+
+
+def _layer_measure(grid: Sequence[cirq.GridQubit]) -> cirq.Circuit:
+    moment = []
+    for i in range(len(grid) // 2):
+        moment.append(cirq.measure(grid[2 * i], key="m"))
+    return cirq.Circuit.from_moments(cirq.Moment(moment))
+
+
+def _change_basis(grid: Sequence[cirq.GridQubit]) -> cirq.Circuit:
+    """change the basis so that the matter sites encode the gauge charge."""
+    n = len(grid)
+    moment_1 = []
+    moment_2 = []
+    moment_h = []
+    for i in range(0, n // 2):
+        q1 = grid[(2 * i)]
+        q2 = grid[2 * i + 1]
+        q3 = grid[(2 * i + 2) % n]
+        moment_1.append(cirq.CZ(q1, q2))
+        moment_2.append(cirq.CZ(q3, q2))
+        moment_h.append(cirq.H(q2))
+    return cirq.Circuit.from_moments(
+        cirq.Moment(moment_h),
+        cirq.Moment(moment_1),
+        cirq.Moment(moment_2),
+        cirq.Moment(moment_h),
+    )
+
+
+def _energy_bump_initial_state(
+    grid, h: float, matter_config: InitialState, excited_qubits: Sequence[cirq.GridQubit]
+) -> cirq.Circuit:
+    """Circuit for energy bump initial state."""
+
+    theta = np.arctan(h)
+    moment = []
+    for i in range(len(grid)):
+        q = grid[i]
+        if i % 2 == 1:
+            if q in excited_qubits:
+                moment.append(cirq.ry(np.pi + theta).on(q))
+            else:
+                moment.append(cirq.ry(theta).on(q))
+
+        else:
+            if matter_config.value == InitialState.SINGLE_SECTOR.value:
+                moment.append(cirq.H(q))
+    return cirq.Circuit.from_moments(moment)
+
+
+def get_1d_dfl_experiment_circuits(
+    grid: Sequence[cirq.GridQubit],
+    initial_state: InitialState,
+    n_cycles: Sequence[int] | npt.NDArray,
+    excited_qubits: Sequence[cirq.GridQubit],
+    dt: float,
+    h: float,
+    mu: float,
+    n_instances: int = 10,
+    two_qubit_gate: TwoQubitGate = TwoQubitGate.CZ,
+    basis: Basis = Basis.DUAL,
+) -> List[cirq.Circuit]:
+    """Generates the circuits needed for the 1D DFL experiment.
+
+    Args:
+        grid: The 1D sequence of qubits used in the experiment.
+        initial_state: The initial state preparation. Use an Enum member from
+            InitialState (SINGLE_SECTOR or SUPERPOSITION).
+        n_cycles: The number of Trotter steps (cycles) to simulate.
+        excited_qubits: Qubits to be excited in the initial state.
+        dt: The time step size for the Trotterization.
+        h: The gauge field strength coefficient.
+        mu: The matter field strength coefficient.
+        n_instances: The number of instances to generate.
+        two_qubit_gate: The type of two-qubit gate to use in the Trotter step.
+            Use an Enum member from TwoQubitGate (CZ or CPHASE).
+        basis: The basis for the final circuit structure. Use an Enum member from
+            Basis (LGT or DUAL).
+
+    Returns:
+        A list of all generated cirq.Circuit objects.
+
+    Raises:
+        ValueError: If an invalid option for `initial_state` or
+            `basis` is given.
+    """
+    if initial_state.value == InitialState.SINGLE_SECTOR.value:
+        initial_circuit = _energy_bump_initial_state(
+            grid, h, InitialState.SINGLE_SECTOR, excited_qubits
+        )
+    elif initial_state.value == InitialState.SUPERPOSITION.value:
+        initial_circuit = _energy_bump_initial_state(
+            grid, h, InitialState.SUPERPOSITION, excited_qubits
+        )
+    else:
+        raise ValueError("Invalid initial state")
+    circuits = []
+    for n_cycle in tqdm(n_cycles):
+        print(int(np.max([0, n_cycle - 1])))
+        circ = initial_circuit + trotter_circuit(
+            grid, n_cycle, dt, h, mu, two_qubit_gate
+        )
+        if basis.value == Basis.LGT.value:
+            circ += _change_basis(grid)
+        elif basis.value == Basis.DUAL.value:
+            pass
+        else:
+            raise ValueError("Invalid option for basis")
+        for _ in range(n_instances):
+
+            if basis.value == Basis.LGT.value:
+                circ_z = circ + cirq.measure([q for q in grid], key="m")
+            elif basis.value == Basis.DUAL.value:
+                circ_z = (
+                    circ
+                    + _layer_hadamard(grid, "matter")
+                    + cirq.measure([q for q in grid], key="m")
+                )
+            else:
+                raise ValueError("Invalid option for basis")
+            circ_x = (
+                circ
+                + _layer_hadamard(grid, "all")
+                + cirq.measure([q for q in grid], key="m")
+            )
+            circuits.append(circ_z)
+            circuits.append(circ_x)
+    return circuits