✨ Add error correction module with Shor and Steane logical circuit transpilers

CHANGELOG.md

@@ -33,6 +33,8 @@ that minor releases may include breaking changes.
 - ✨ Add quantum teleportation benchmark ([#1045]) ([**@AsharHusain**])
 - ✨ Add ML-QAE benchmark ([#1044]) ([**@algovista-collab**])
 - ✨ Add Superdense Coding benchmark ([#1037]) ([**@Anshu666666**])
+- ✨ Add `encoding` option for Steane's and Shor's codes ([#930])
+  ([**@Felix-Gundlach**], [**@emilkanic0909**], [**@SalehAlsherif**])
 
 ### Changed
 
@@ -336,6 +338,7 @@ _📚 Refer to the [GitHub Release Notes] for previous changelogs._
 [#997]: https://github.com/munich-quantum-toolkit/bench/pull/997
 [#952]: https://github.com/munich-quantum-toolkit/bench/pull/952
 [#946]: https://github.com/munich-quantum-toolkit/bench/pull/946
+[#930]: https://github.com/munich-quantum-toolkit/bench/pull/930
 [#925]: https://github.com/munich-quantum-toolkit/bench/pull/925
 [#914]: https://github.com/munich-quantum-toolkit/bench/pull/914
 [#895]: https://github.com/munich-quantum-toolkit/bench/pull/895
@@ -392,6 +395,9 @@ _📚 Refer to the [GitHub Release Notes] for previous changelogs._
 [**@TomasVF**]: https://github.com/TomasVF
 [**@flowerthrower**]: https://github.com/flowerthrower
 [**@johanneswittmann9**]: https://github.com/johanneswittmann9
+[**@Felix-Gundlach**]: https://github.com/Felix-Gundlach
+[**@emilkanic0909**]: https://github.com/emilkanic0909
+[**@SalehAlsherif**]: https://github.com/SalehAlsherif
 [**@cnYui**]: https://github.com/cnYui
 [**@algovista-collab**]: https://github.com/algovista-collab
 [**@Anshu666666**]: https://github.com/Anshu666666

docs/parameter.md

@@ -64,6 +64,21 @@ print(get_available_device_names())
   the mirror. Circuits that Qiskit cannot invert, for example those with
   mid-circuit measurements, resets, or unsupported control flow, raise
   `ValueError`. Use `False` to generate these circuits without a mirror.
+- `encoding`: Error-correcting code applied to the circuit. Only the ALG level
+  supports it; other levels ignore it with a warning. Gates without a
+  transversal realization become placeholders: opaque logical gadgets named
+  `<code>_ideal_logical_<gate>`, for example `steane_ideal_logical_t`. OpenQASM
+  3 export does not support placeholders, so save encoded circuits as QPY.
+  Rotations are approximated, so gate counts can differ between Qiskit versions.
+
+Possible values for `encoding`:
+
+```{code-cell} ipython3
+:tags: [hide-input]
+from mqt.bench.error_correction import get_available_encoding_names
+
+print(get_available_encoding_names())
+```
 
 ## Native Gate-Set Support
 

src/mqt/bench/benchmark_generation.py

@@ -11,6 +11,7 @@
 from __future__ import annotations
 
 import json
+import warnings
 from copy import deepcopy
 from enum import Enum, auto
 from typing import TYPE_CHECKING, Unpack, assert_never, overload
@@ -26,6 +27,7 @@
 from qiskit.version import VERSION as QISKIT_VERSION
 
 from .benchmarks import create_circuit
+from .error_correction import get_available_encoding_names, get_transpiler
 from .targets.gatesets import get_target_for_gateset
 from .targets.gatesets._compilation import prepare_target
 from .targets.gatesets.ibm import configure_fractional_angles
@@ -116,13 +118,15 @@ def _record_generation(
     target: Target | None = None,
     opt_level: int | None = None,
     mirror: bool = False,
+    encoding: str = "",
 ) -> None:
     """Attach the compilation settings to the circuit's generation record."""
     generation.update({
         "level": level.name.lower(),
         "opt_level": opt_level,
         "target": target.description if target is not None else None,
         "mirror": mirror or generation.get("mirror", False),
+        "encoding": encoding or generation.get("encoding"),
     })
     qc.metadata = (qc.metadata or {}) | {"mqt_bench_generation": generation}
 
@@ -233,6 +237,7 @@ def get_benchmark_alg(
     benchmark: str,
     circuit_size: int,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -244,6 +249,7 @@ def get_benchmark_alg(
     benchmark: QuantumCircuit,
     circuit_size: None = None,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -255,6 +261,7 @@ def get_benchmark_alg(
     benchmark: str | QuantumCircuit,
     circuit_size: int | None = None,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -265,6 +272,7 @@ def get_benchmark_alg(
     benchmark: str | QuantumCircuit,
     circuit_size: int | None = None,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -274,19 +282,30 @@ def get_benchmark_alg(
     Arguments:
         benchmark: QuantumCircuit or name of the benchmark to be generated
         circuit_size: Input for the benchmark creation, in most cases this is equal to the qubit number
+        encoding: Name of an error-correcting code from `get_available_encoding_names()`, or "" for none.
         generate_mirror_circuit: If True, generates the mirror version (U @ U.inverse()) of the benchmark.
         random_parameters: If True, assigns random parameters to the circuit's parameters if they exist.
         kwargs: Additional keyword arguments passed to the circuit creation.
 
     Returns:
         Qiskit::QuantumCircuit representing the raw benchmark circuit without any hardware-specific compilation or mapping.
     """
+    valid_encodings = {"", *get_available_encoding_names()}
+    if encoding not in valid_encodings:
+        msg = f"Invalid `encoding` '{encoding}'. Must be one of {valid_encodings}."
+        raise ValueError(msg)
+
     qc, generation = _get_circuit(benchmark, circuit_size, random_parameters, **kwargs)
     if qc is benchmark:
         qc = qc.copy()
-    _record_generation(qc, BenchmarkLevel.ALG, generation, mirror=generate_mirror_circuit)
+    _record_generation(qc, BenchmarkLevel.ALG, generation, mirror=generate_mirror_circuit, encoding=encoding)
     if generate_mirror_circuit:
-        return _create_mirror_circuit(qc, inplace=True)
+        qc = _create_mirror_circuit(qc, inplace=True)
+
+    if encoding:
+        # The encoded circuit keeps the metadata, including the generation record.
+        qc = get_transpiler(encoding)(qc).transpile()
+
     return qc
 
 
@@ -574,6 +593,7 @@ def get_benchmark(
     target: Target | None = None,
     opt_level: int = 2,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -588,6 +608,7 @@ def get_benchmark(
     target: Target | None = None,
     opt_level: int = 2,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -602,6 +623,7 @@ def get_benchmark(
     target: Target | None = None,
     opt_level: int = 2,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -615,6 +637,7 @@ def get_benchmark(
     target: Target | None = None,
     opt_level: int = 2,
     *,
+    encoding: str = "",
     generate_mirror_circuit: bool = False,
     random_parameters: bool = True,
     **kwargs: Unpack[ConfigurationOptions],
@@ -628,19 +651,29 @@ def get_benchmark(
         target: `~qiskit.transpiler.target.Target` for the benchmark generation
                 (only used for "nativegates" and "mapped" level)
         opt_level: Optimization level to be used by the transpiler.
+        encoding: Name of an error-correcting code from `get_available_encoding_names()`, or "" for none.
+                Only supported for `BenchmarkLevel.ALG`; ignored (with a warning) for other levels.
         generate_mirror_circuit: If True, generates the mirror version (U @ U.inverse()) of the benchmark.
         random_parameters: If True, assigns random parameters to the circuit's parameters if they exist.
         kwargs: Additional keyword arguments passed to the circuit creation.
 
     Returns:
         Qiskit::QuantumCircuit object representing the benchmark with the selected options
     """
+    if level is not BenchmarkLevel.ALG and encoding:
+        warnings.warn(
+            f"`encoding` is only supported for BenchmarkLevel.ALG and will be ignored for level={level.name}.",
+            UserWarning,
+            stacklevel=2,
+        )
+
     if level is BenchmarkLevel.ALG:
         return get_benchmark_alg(
             benchmark=benchmark,
             circuit_size=circuit_size,
             generate_mirror_circuit=generate_mirror_circuit,
             random_parameters=random_parameters,
+            encoding=encoding,
             **kwargs,
         )
 

src/mqt/bench/benchmarks/seven_qubit_steane_code.py

@@ -13,127 +13,14 @@
 from qiskit import ClassicalRegister
 from qiskit.circuit import AncillaRegister, QuantumCircuit, QuantumRegister
 
-from ._registry import register_benchmark
-
-
-def _get_seven_qubit_steane_code_encoding_circuit() -> QuantumCircuit:
-    """Create the 7-qubit Steane code encoding circuit.
-
-    Encodes qubit 0 into the 7-qubit Steane code logical state:
-        - |0> -> (|0000000> + |1010101> + |0110011> + |1100110> + |0001111> + |1011010> + |0111100> + |1101001>)
-        - |1> -> (|1111111> + |0101010> + |1001100> + |0011001> + |1110000> + |0100101> + |1000011> + |0010110>).
-
-    Returns:
-        QuantumCircuit: 7-qubit encoding circuit.
-    """
-    out = QuantumCircuit(7)
-    # H
-    out.h(4)
-    out.h(5)
-    out.h(6)
-    # CNOT from 0
-    out.cx(0, 1)
-    out.cx(0, 2)
-    # CNOT from 6
-    out.cx(6, 3)
-    out.cx(6, 1)
-    out.cx(6, 0)
-    # CNOT from 5
-    out.cx(5, 3)
-    out.cx(5, 2)
-    out.cx(5, 0)
-    # CNOT from 4
-    out.cx(4, 3)
-    out.cx(4, 2)
-    out.cx(4, 1)
-    return out
-
-
-def _get_seven_qubit_steane_code_decoding_circuit() -> QuantumCircuit:
-    """Create the 7-qubit Steane code decoding circuit.
-
-    Reverses the encoding operation to extract the logical qubit back to qubit 0.
-
-    Returns:
-        QuantumCircuit: 7-qubit decoding circuit (qubit 0 is the output qubit).
-    """
-    return _get_seven_qubit_steane_code_encoding_circuit().inverse()
-
+from mqt.bench.components.steane_circuit_components import (
+    apply_seven_qubit_steane_code_correction,
+    get_seven_qubit_steane_code_decoding_circuit,
+    get_seven_qubit_steane_code_encoding_circuit,
+    get_seven_qubit_steane_code_syndrome_extraction_circuit,
+)
 
-def _get_seven_qubit_steane_code_syndrome_extraction_circuit() -> QuantumCircuit:
-    """Create the syndrome extraction circuit for the 7-qubit Steane code.
-
-    Extracts bit-flip and phase-flip syndromes using 6 ancilla qubits (3 for each type).
-
-    Bit-flip syndrome extraction:
-        Syndrome bits measure the parity of specific qubit subsets corresponding to
-        the X-stabilizer generators.
-
-    Phase-flip syndrome extraction:
-        Uses Hadamard gates to convert from Z to X basis, and control/target swapped
-        CNOTs to extract the phase-flip syndrome
-
-    Syndrome mapping: The 3-bit syndrome value (1-7) directly identifies which
-    data qubit experienced an error. Syndrome 0 indicates no error.
-
-    Returns:
-        QuantumCircuit: 13-qubit circuit (qubits 0-6 are data, 7-9 are bit-flip
-            syndrome ancillas, 10-12 are phase-flip syndrome ancillas).
-    """
-    logical_qubit, bit_flip_syndrome, phase_flip_syndrome = QuantumRegister(7), AncillaRegister(3), AncillaRegister(3)
-    out = QuantumCircuit(logical_qubit, bit_flip_syndrome, phase_flip_syndrome)
-    # Bit-flip
-    for ctrl in (0, 2, 4, 6):
-        out.cx(logical_qubit[ctrl], bit_flip_syndrome[0])
-    for ctrl in (1, 2, 5, 6):
-        out.cx(logical_qubit[ctrl], bit_flip_syndrome[1])
-    for ctrl in (3, 4, 5, 6):
-        out.cx(logical_qubit[ctrl], bit_flip_syndrome[2])
-    # Phase-flip
-    for i in range(3):
-        out.h(phase_flip_syndrome[i])
-    for targ in (0, 2, 4, 6):
-        out.cx(phase_flip_syndrome[0], logical_qubit[targ])
-    for targ in (1, 2, 5, 6):
-        out.cx(phase_flip_syndrome[1], logical_qubit[targ])
-    for targ in (3, 4, 5, 6):
-        out.cx(phase_flip_syndrome[2], logical_qubit[targ])
-    for i in range(3):
-        out.h(phase_flip_syndrome[i])
-    return out
-
-
-def _apply_seven_qubit_steane_code_correction(
-    qc: QuantumCircuit,
-    logical_qubit: QuantumRegister,
-    bit_flip_syndrome: AncillaRegister,
-    phase_flip_syndrome: AncillaRegister,
-    bit_flip_syndrome_measurement: ClassicalRegister,
-    phase_flip_syndrome_measurement: ClassicalRegister,
-) -> None:
-    """Apply error correction based on syndrome measurements.
-
-    Measures the 6 syndrome qubits and conditionally applies X/Z gates to correct
-    single-qubit errors on any of the 7 data qubits.
-
-    Arguments:
-        qc: The quantum circuit to modify.
-        logical_qubit: Register containing the 7 data qubits.
-        bit_flip_syndrome: Register containing the 3 bit-flip syndrome qubits.
-        phase_flip_syndrome: Register containing the 3 phase-flip syndrome qubits.
-        bit_flip_syndrome_measurement: Classical register for bit-flip syndrome results.
-        phase_flip_syndrome_measurement: Classical register for phase-flip syndrome results.
-    """
-    qc.measure(bit_flip_syndrome, bit_flip_syndrome_measurement)
-    qc.measure(phase_flip_syndrome, phase_flip_syndrome_measurement)
-    # Bit-flip correction: syndrome value directly indicates which qubit to correct
-    for i in range(7):
-        with qc.if_test((bit_flip_syndrome_measurement, i + 1)):
-            qc.x(logical_qubit[i])
-    # Phase-flip correction: syndrome value directly indicates which qubit to correct
-    for i in range(7):
-        with qc.if_test((phase_flip_syndrome_measurement, i + 1)):
-            qc.z(logical_qubit[i])
+from ._registry import register_benchmark
 
 
 def _create_single_logical_qubit_circuit(index: int) -> QuantumCircuit:
@@ -164,20 +51,20 @@ def _create_single_logical_qubit_circuit(index: int) -> QuantumCircuit:
     )
     # == Encoding ==
     qc.compose(
-        _get_seven_qubit_steane_code_encoding_circuit(),
+        get_seven_qubit_steane_code_encoding_circuit(),
         qubits=logical_qubit[:],
         inplace=True,
     )
     qc.barrier()
     # == Syndrome extraction ==
     qc.compose(
-        _get_seven_qubit_steane_code_syndrome_extraction_circuit(),
+        get_seven_qubit_steane_code_syndrome_extraction_circuit(),
         qubits=logical_qubit[:] + bit_flip_syndrome[:] + phase_flip_syndrome[:],
         inplace=True,
     )
     qc.barrier()
     # == Error correction ==
-    _apply_seven_qubit_steane_code_correction(
+    apply_seven_qubit_steane_code_correction(
         qc,
         logical_qubit,
         bit_flip_syndrome,
@@ -188,7 +75,7 @@ def _create_single_logical_qubit_circuit(index: int) -> QuantumCircuit:
     qc.barrier()
     # == Decoding ==
     qc.compose(
-        _get_seven_qubit_steane_code_decoding_circuit(),
+        get_seven_qubit_steane_code_decoding_circuit(),
         qubits=logical_qubit[:],
         inplace=True,
     )