[Refactoring] Use Readout from Pyqtorch (#599)

docs/tutorials/realistic_sims/noise.md

@@ -92,23 +92,12 @@ print(f"noiseless = {noiseless_samples}") # markdown-exec: hide
 print(f"noisy = {noisy_samples}") # markdown-exec: hide
 ```
 
-Note we can apply directly the method `apply_readout_noise` to the noiseless samples as follows:
-
-```python exec="on" source="material-block" session="noise" result="json"
-from qadence.noise import apply_readout_noise
-altered_samples = apply_readout_noise(noise, noiseless_samples)
-
-print(f"noiseless = {noiseless_samples}") # markdown-exec: hide
-print(f"noisy = {noisy_samples}") # markdown-exec: hide
-```
-
 It is possible to pass options to the noise model. In the previous example, a noise matrix is implicitly computed from a
 uniform distribution. The `option` dictionary argument accepts the following options:
 
 - `seed`: defaulted to `None`, for reproducibility purposes
 - `error_probability`: defaulted to 0.1, a bit flip probability
 - `noise_distribution`: defaulted to `WhiteNoise.UNIFORM`, for non-uniform noise distributions
-- `noise_matrix`: defaulted to `None`, if the noise matrix is known from third-party experiments, _i.e._ hardware calibration.
 
 Noisy simulations go hand-in-hand with measurement protocols discussed in the previous [section](measurements.md), to assess the impact of noise on expectation values. In this case, both measurement and noise protocols have to be defined appropriately. Please note that a noise protocol without a measurement protocol will be ignored for expectation values computations.
 

qadence/backends/pulser/backend.py

@@ -25,7 +25,6 @@
 from qadence.mitigations import Mitigations
 from qadence.mitigations.protocols import apply_mitigation
 from qadence.noise import NoiseHandler
-from qadence.noise.protocols import apply_readout_noise
 from qadence.overlap import overlap_exact
 from qadence.register import Register
 from qadence.transpile import transpile
@@ -311,8 +310,6 @@ def sample(
             from qadence.transpile import invert_endianness
 
             samples = invert_endianness(samples)
-        if noise is not None:
-            samples = apply_readout_noise(noise=noise, samples=samples)
         if mitigation is not None:
             logger.warning(
                 "Mitigation protocol is deprecated. Use qadence-protocols instead.",

qadence/backends/pyqtorch/backend.py

@@ -23,7 +23,6 @@
 from qadence.measurements import Measurements
 from qadence.mitigations.protocols import Mitigations, apply_mitigation
 from qadence.noise import NoiseHandler
-from qadence.noise.protocols import apply_readout_noise
 from qadence.transpile import (
     chain_single_qubit_ops,
     flatten,
@@ -34,7 +33,7 @@
 from qadence.types import BackendName, Endianness, Engine
 
 from .config import Configuration, default_passes
-from .convert_ops import convert_block
+from .convert_ops import convert_block, convert_readout_noise
 
 logger = getLogger(__name__)
 
@@ -65,7 +64,16 @@ def circuit(self, circuit: QuantumCircuit) -> ConvertedCircuit:
             circuit = transpile(*passes)(circuit)
 
         ops = convert_block(circuit.block, n_qubits=circuit.n_qubits, config=self.config)
-        native = pyq.QuantumCircuit(circuit.n_qubits, ops)
+        readout_noise = (
+            convert_readout_noise(circuit.n_qubits, self.config.noise)
+            if self.config.noise
+            else None
+        )
+        native = pyq.QuantumCircuit(
+            circuit.n_qubits,
+            ops,
+            readout_noise,
+        )
         return ConvertedCircuit(native=native, abstract=circuit, original=original_circ)
 
     def observable(self, observable: AbstractBlock, n_qubits: int) -> ConvertedObservable:
@@ -116,6 +124,9 @@ def _batched_expectation(
         noise: NoiseHandler | None = None,
         endianness: Endianness = Endianness.BIG,
     ) -> Tensor:
+        if noise and circuit.native.readout_noise is None:
+            readout = convert_readout_noise(circuit.abstract.n_qubits, noise)
+            circuit.native.readout_noise = readout
         state = self.run(
             circuit,
             param_values=param_values,
@@ -152,6 +163,11 @@ def _looped_expectation(
                 "Looping expectation does not make sense with batched initial state. "
                 "Define your initial state with `batch_size=1`"
             )
+
+        if noise and circuit.native.readout_noise is None:
+            readout = convert_readout_noise(circuit.abstract.n_qubits, noise)
+            circuit.native.readout_noise = readout
+
         list_expvals = []
         observables = observable if isinstance(observable, list) else [observable]
         for vals in to_list_of_dicts(param_values):
@@ -206,12 +222,13 @@ def sample(
         elif state is not None and pyqify_state:
             n_qubits = circuit.abstract.n_qubits
             state = pyqify(state, n_qubits) if pyqify_state else state
+        if noise and circuit.native.readout_noise is None:
+            readout = convert_readout_noise(circuit.abstract.n_qubits, noise)
+            circuit.native.readout_noise = readout
         samples: list[Counter] = circuit.native.sample(
             state=state, values=param_values, n_shots=n_shots
         )
         samples = invert_endianness(samples) if endianness != Endianness.BIG else samples
-        if noise is not None:
-            samples = apply_readout_noise(noise=noise, samples=samples)
         if mitigation is not None:
             logger.warning(
                 "Mitigation protocol is deprecated. Use qadence-protocols instead.",

qadence/backends/pyqtorch/config.py

@@ -8,6 +8,7 @@
 
 from qadence.analog import add_background_hamiltonian
 from qadence.backend import BackendConfiguration
+from qadence.noise import NoiseHandler
 from qadence.transpile import (
     blockfn_to_circfn,
     chain_single_qubit_ops,
@@ -63,3 +64,6 @@ class Configuration(BackendConfiguration):
 
     Loop over the batch of parameters to only allocate a single wavefunction at any given time.
     """
+
+    noise: NoiseHandler | None = None
+    """NoiseHandler containing readout noise applied in backend."""

qadence/backends/pyqtorch/convert_ops.py

@@ -321,7 +321,16 @@ def convert_block(
         )
 
 
-def convert_digital_noise(noise: NoiseHandler) -> pyq.noise.NoiseProtocol:
+def convert_digital_noise(noise: NoiseHandler) -> pyq.noise.NoiseProtocol | None:
+    """Convert the digital noise into pyqtorch NoiseProtocol.
+
+    Args:
+        noise (NoiseHandler): Noise to convert.
+
+    Returns:
+        pyq.noise.NoiseProtocol | None: Pyqtorch native noise protocol
+            if there are any digital noise protocols.
+    """
     digital_part = noise.filter(NoiseProtocol.DIGITAL)
     if digital_part is None:
         return None
@@ -331,3 +340,20 @@ def convert_digital_noise(noise: NoiseHandler) -> pyq.noise.NoiseProtocol:
             for proto, option in zip(digital_part.protocol, digital_part.options)
         ]
     )
+
+
+def convert_readout_noise(n_qubits: int, noise: NoiseHandler) -> pyq.noise.ReadoutNoise | None:
+    """Convert the readout noise into pyqtorch ReadoutNoise.
+
+    Args:
+        n_qubits (int): Number of qubits
+        noise (NoiseHandler):  Noise to convert.
+
+    Returns:
+        pyq.noise.ReadoutNoise | None: Pyqtorch native ReadoutNoise instance
+            if readout is is noise.
+    """
+    readout_part = noise.filter(NoiseProtocol.READOUT)
+    if readout_part is None:
+        return None
+    return pyq.noise.ReadoutNoise(n_qubits, **readout_part.options[0])

qadence/mitigations/readout.py

@@ -10,9 +10,10 @@
 from scipy.linalg import norm
 from scipy.optimize import LinearConstraint, minimize
 
+from qadence.backends.pyqtorch.convert_ops import convert_readout_noise
 from qadence.mitigations.protocols import Mitigations
 from qadence.noise.protocols import NoiseHandler
-from qadence.types import NoiseProtocol, ReadOutOptimization
+from qadence.types import ReadOutOptimization
 
 
 def corrected_probas(p_corr: npt.NDArray, T: npt.NDArray, p_raw: npt.NDArray) -> np.double:
@@ -88,13 +89,18 @@ def mitigation_minimization(
     Returns:
         Mitigated counts computed by the algorithm
     """
-    protocol, options = noise.protocol[-1], noise.options[-1]
-    if protocol != NoiseProtocol.READOUT:
-        raise ValueError("Specify a noise source of type NoiseProtocol.READOUT.")
-    noise_matrices = options.get("noise_matrix", options["confusion_matrices"])
-    optimization_type = mitigation.options.get("optimization_type", ReadOutOptimization.MLE)
+
     n_qubits = len(list(samples[0].keys())[0])
+    readout_noise = convert_readout_noise(n_qubits, noise)
+    if readout_noise is None:
+        raise ValueError("Specify a noise source of type NoiseProtocol.READOUT.")
     n_shots = sum(samples[0].values())
+    noise_matrices = readout_noise.confusion_matrices
+    if readout_noise.confusion_matrices.numel() == 0:
+        readout_noise.create_noise_matrix(n_shots)
+        noise_matrices = readout_noise.confusion_matrices
+    optimization_type = mitigation.options.get("optimization_type", ReadOutOptimization.MLE)
+
     corrected_counters: list[Counter] = []
 
     if optimization_type == ReadOutOptimization.CONSTRAINED:

qadence/noise/__init__.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from .protocols import NoiseHandler, apply_readout_noise
+from .protocols import NoiseHandler
 
 # Modules to be automatically added to the qadence namespace
-__all__ = ["NoiseHandler", "apply_readout_noise"]
+__all__ = ["NoiseHandler"]

qadence/noise/protocols.py

@@ -1,15 +1,10 @@
 from __future__ import annotations
 
-import importlib
 from itertools import compress
-from typing import Any, Callable, Counter, cast
+from typing import Any
 
 from qadence.types import NoiseEnum, NoiseProtocol
 
-PROTOCOL_TO_MODULE = {
-    "Readout": "qadence.noise.readout",
-}
-
 
 class NoiseHandler:
     """A container for multiple sources of noise.
@@ -106,16 +101,6 @@ def __repr__(self) -> str:
             ]
         )
 
-    def get_noise_fn(self, index_protocol: int) -> Callable:
-        try:
-            module = importlib.import_module(PROTOCOL_TO_MODULE[self.protocol[index_protocol]])
-        except KeyError:
-            ImportError(
-                f"The module for the protocol {self.protocol[index_protocol]} is not found."
-            )
-        fn = getattr(module, "add_noise")
-        return cast(Callable, fn)
-
     def append(self, other: NoiseHandler | list[NoiseHandler]) -> None:
         """Append noises.
 
@@ -163,8 +148,8 @@ def _from_dict(cls, d: dict | None) -> NoiseHandler | None:
     def list(cls) -> list:
         return list(filter(lambda el: not el.startswith("__"), dir(cls)))
 
-    def filter(self, protocol: NoiseEnum) -> NoiseHandler | None:
-        is_protocol: list = [isinstance(p, protocol) for p in self.protocol]  # type: ignore[arg-type]
+    def filter(self, protocol: NoiseEnum | str) -> NoiseHandler | None:
+        is_protocol: list = [p == protocol or isinstance(p, protocol) for p in self.protocol]  # type: ignore[arg-type]
         return (
             NoiseHandler(
                 list(compress(self.protocol, is_protocol)),
@@ -215,27 +200,3 @@ def dephasing(self, *args: Any, **kwargs: Any) -> NoiseHandler:
     def readout(self, *args: Any, **kwargs: Any) -> NoiseHandler:
         self.append(NoiseHandler(NoiseProtocol.READOUT, *args, **kwargs))
         return self
-
-
-def apply_readout_noise(noise: NoiseHandler, samples: list[Counter]) -> list[Counter]:
-    """Apply readout noise to samples if provided.
-
-    Args:
-        noise (NoiseHandler): Noise to apply.
-        samples (list[Counter]): Samples to alter
-
-    Returns:
-        list[Counter]: Altered samples.
-    """
-    if noise.protocol[-1] == NoiseProtocol.READOUT:
-        error_fn = noise.get_noise_fn(-1)
-        # Get the number of qubits from the sample keys.
-        n_qubits = len(list(samples[0].keys())[0])
-        # Get the number of shots from the sample values.
-        n_shots = sum(samples[0].values())
-        noisy_samples: list = error_fn(
-            counters=samples, n_qubits=n_qubits, options=noise.options[-1], n_shots=n_shots
-        )
-        return noisy_samples
-    else:
-        return samples