Quantum-related components of a QUBO solver

Drive Shapping

BaseDriveShaper(instance, config, backend)

Bases: ABC

Abstract base class for generating Qoolqit drives based on a QUBO problem.

This class transforms the structure of a QUBOInstance into a quantum waveform sequence or drive that can be applied to a physical register. The register is passed at the time of drive generation, not during initialization.

ATTRIBUTE	DESCRIPTION
instance	The QUBO problem instance. TYPE: QUBOInstance
config	The solver configuration. TYPE: SolverConfig
drive	A saved current drive obtained by generate. TYPE: Drive
backend	Backend to use. TYPE: Backend
device	Device from backend. TYPE: Device

Initialize the drive shaping module with a QUBO instance.

PARAMETER	DESCRIPTION
instance	The QUBO problem instance. TYPE: QUBOInstance
config	The solver configuration. TYPE: SolverConfig
backend	Backend to use. TYPE: Backend

Source code in qubosolver/pipeline/drive.py

def __init__(self, instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend):
    """
    Initialize the drive shaping module with a QUBO instance.

    Args:
        instance (QUBOInstance): The QUBO problem instance.
        config (SolverConfig): The solver configuration.
        backend (Backend): Backend to use.
    """
    self.instance: QUBOInstance = instance
    self.config: SolverConfig = config
    self.drive: Drive | None = None
    self.backend = backend
    self.device = self.config.device

    # check if device allow DMM
    self.dmm = self.config.drive_shaping.dmm and (
        len(list(self.config.device._device.dmm_channels.keys())) > 0
    )

generate(register) abstractmethod

Generate a drive based on the problem and the provided register.

PARAMETER	DESCRIPTION
register	The physical register layout. TYPE: Register

RETURNS	DESCRIPTION
Drive	A generated Drive. TYPE: Drive
QUBOSolution	An instance of the qubo solution TYPE: QUBOSolution

Source code in qubosolver/pipeline/drive.py

@abstractmethod
def generate(
    self,
    register: Register,
) -> tuple[Drive, QUBOSolution]:
    """
    Generate a drive based on the problem and the provided register.

    Args:
        register (Register): The physical register layout.

    Returns:
        Drive: A generated Drive.
        QUBOSolution: An instance of the qubo solution
    """
    pass

HeuristicDriveShaper(instance, config, backend)

Bases: BaseDriveShaper

Heuristic schedule drive shaper.

With DMM

Without DMM

Source code in qubosolver/pipeline/drive.py

def __init__(self, instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend):
    """
    Initialize the drive shaping module with a QUBO instance.

    Args:
        instance (QUBOInstance): The QUBO problem instance.
        config (SolverConfig): The solver configuration.
        backend (Backend): Backend to use.
    """
    self.instance: QUBOInstance = instance
    self.config: SolverConfig = config
    self.drive: Drive | None = None
    self.backend = backend
    self.device = self.config.device

    # check if device allow DMM
    self.dmm = self.config.drive_shaping.dmm and (
        len(list(self.config.device._device.dmm_channels.keys())) > 0
    )

OptimizedDriveShaper(instance, config, backend)

Bases: BaseDriveShaper

Drive shaper that uses optimization to find the best drive parameters for solving QUBOs. Returns an optimized drive, the bitstrings, their counts, probabilities, and costs.

ATTRIBUTE	DESCRIPTION
drive	current drive. TYPE: Drive
best_cost	Current best cost. TYPE: float
best_bitstring	Current best bitstring. TYPE: Tensor | list
bitstrings	List of current bitstrings obtained. TYPE: Tensor | list
counts	Frequencies of bitstrings. TYPE: Tensor | list
probabilities	Probabilities of bitstrings. TYPE: Tensor | list
costs	Qubo cost. TYPE: Tensor | list
optimized_custom_qubo_cost	Apply a different qubo cost evaluation during optimization. Must be defined as: def optimized_custom_qubo_cost(bitstring: str, QUBO: torch.Tensor) -> float. Defaults to None, meaning we use the default QUBO evaluation. TYPE: Callable[[str, Tensor], float]
optimized_custom_objective_fn	For bayesian optimization, one can change the output of self.run_simulation to optimize differently. Instead of using the best cost out of the samples, one can change the objective for an average, or any function out of the form cost_eval = optimized_custom_objective_fn(bitstrings, counts, probabilities, costs, best_cost, best_bitstring) Defaults to None, which means we optimize using the best cost out of the samples. TYPE: Callable[[list, list, list, list, float, str], float]
optimized_callback_objective	Apply a callback during bayesian optimization. Only accepts one input dictionary created during optimization d = {"x": x, "cost_eval": cost_eval} hence should be defined as: def callback_fn(d: dict) -> None: Defaults to None, which means no callback is applied. TYPE: Callable[..., None]

Instantiate an OptimizedDriveShaper.

PARAMETER	DESCRIPTION
instance	Qubo instance. TYPE: QUBOInstance
config	Configuration for solving. TYPE: SolverConfig
backend	Backend to use during optimization. TYPE: Backend

Source code in qubosolver/pipeline/drive.py

def __init__(
    self,
    instance: QUBOInstance,
    config: SolverConfig,
    backend: concepts.Backend,
):
    """Instantiate an `OptimizedDriveShaper`.

    Args:
        instance (QUBOInstance): Qubo instance.
        config (SolverConfig): Configuration for solving.
        backend (Backend): Backend to use during optimization.

    """
    super().__init__(instance, config, backend)

    self.drive = None
    self.best_cost = None
    self.best_bitstring = None
    self.best_params = None
    self.bitstrings = None
    self.counts = None
    self.probabilities = None
    self.costs = None
    self.optimized_custom_qubo_cost = self.config.drive_shaping.optimized_custom_qubo_cost
    self.optimized_custom_objective_fn = self.config.drive_shaping.optimized_custom_objective
    self.optimized_callback_objective = self.config.drive_shaping.optimized_callback_objective

build_drive(params)

Build the drive waveform from a normalised parameter vector.

PARAMETER	DESCRIPTION
params	6 values — 3 amplitude breakpoints then 3 detuning breakpoints, all normalised to [0, 1] (or [-1, 1] for detuning). TYPE: list

RETURNS	DESCRIPTION
Drive	Drive sequence. TYPE: Drive

Source code in qubosolver/pipeline/drive.py

def build_drive(self, params: list) -> Drive:
    """Build the drive waveform from a normalised parameter vector.

    Args:
        params (list): 6 values — 3 amplitude breakpoints then 3 detuning
            breakpoints, all normalised to [0, 1] (or [-1, 1] for detuning).

    Returns:
        Drive: Drive sequence.
    """
    specs = self.device.specs
    max_seq_duration: float = specs["max_duration"] or 1e3
    max_amplitude: float = specs["max_amplitude"] or 1e4
    max_detuning: float = specs["max_abs_detuning"] or 1e4

    amp_params = [1e-9] + list(params[:3]) + [1e-9]
    det_params = list(params[3:])
    amp_params = [p * max_amplitude for p in amp_params]
    det_params = [p * max_detuning for p in det_params]

    amp_wave = InterpolatedWaveform(max_seq_duration, amp_params)
    det_wave = InterpolatedWaveform(max_seq_duration, det_params)

    dmm = None
    final_detuning = det_params[-1]
    if self.dmm and final_detuning > 0:
        dmm = constant_weighted_dmm(
            self.register,
            max_seq_duration,
            self.norm_weights_list,
            final_detuning=-final_detuning,
        )

    shaped_drive = Drive(amplitude=amp_wave, detuning=det_wave, dmm=dmm)

    return shaped_drive

compute_qubo_cost(bitstring, QUBO)

The qubo cost for a single bitstring to apply during optimization.

PARAMETER	DESCRIPTION
bitstring	candidate bitstring. TYPE: str
QUBO	qubo coefficients. TYPE: Tensor

RETURNS	DESCRIPTION
float	respective cost of bitstring. TYPE: float

Source code in qubosolver/pipeline/drive.py

def compute_qubo_cost(self, bitstring: str, QUBO: torch.Tensor) -> float:
    """The qubo cost for a single bitstring to apply during optimization.

    Args:
        bitstring (str): candidate bitstring.
        QUBO (torch.Tensor): qubo coefficients.

    Returns:
        float: respective cost of bitstring.
    """
    if self.optimized_custom_qubo_cost is None:
        return calculate_qubo_cost(bitstring, QUBO)

    return cast(float, self.optimized_custom_qubo_cost(bitstring, QUBO))

generate(register)

Generate a drive via Bayesian optimisation.

PARAMETER	DESCRIPTION
register	The physical register layout. TYPE: Register

RETURNS	DESCRIPTION
Drive	A generated Drive. TYPE: Drive
QUBOSolution	An instance of the qubo solution TYPE: QUBOSolution

Source code in qubosolver/pipeline/drive.py

def generate(
    self,
    register: Register,
) -> tuple[Drive, QUBOSolution]:
    """
    Generate a drive via Bayesian optimisation.

    Args:
        register (Register): The physical register layout.

    Returns:
        Drive: A generated Drive.
        QUBOSolution: An instance of the qubo solution
    """
    # TODO: Harmonize the output of the pulse_shaper generate
    QUBO = self.qubo_coefficients
    self.register = register

    self.norm_weights_list = self._compute_norm_weights()

    n_amp = 3
    n_det = 3

    eps = 0.0001
    zero = eps
    one = 1.0 - eps

    bounds = (
        [(zero, one)] * n_amp + [(-one, -zero)] + [(-one, one)] * (n_det - 2) + [(zero, one)]
    )
    x0 = (
        self.config.drive_shaping.optimized_initial_omega_parameters
        + self.config.drive_shaping.optimized_initial_detuning_parameters
    )

    def objective(x: list[float]) -> float:
        drive = self.build_drive(x)

        try:
            bitstrings, counts, probabilities, costs, cost_eval, best_bitstring = (
                self.run_simulation(
                    self.register,
                    drive,
                    QUBO,
                    convert_to_tensor=False,
                )
            )
            if self.optimized_custom_objective_fn is not None:
                cost_eval = self.optimized_custom_objective_fn(
                    bitstrings,
                    counts,
                    probabilities,
                    costs,
                    cost_eval,
                    best_bitstring,
                )
            if not np.isfinite(cost_eval):
                print(f"[Warning] Non-finite cost encountered: {cost_eval} at x={x}")
                cost_eval = 1e4

        except Exception as e:
            print(f"[Exception] Error during simulation at x={x}: {e}")
            cost_eval = 1e4

        if self.optimized_callback_objective is not None:
            self.optimized_callback_objective({"x": x, "cost_eval": cost_eval})
        return float(cost_eval)

    opt_result = gp_minimize(
        objective,
        bounds,
        x0=x0,
        n_calls=self.config.drive_shaping.optimized_n_calls,
        random_state=self.config.drive_shaping.optimized_seed,
    )

    if opt_result and opt_result.x:
        self.best_params = opt_result.x
        self.drive = self.build_drive(self.best_params)  # type: ignore[arg-type]

        (
            self.bitstrings,
            self.counts,
            self.probabilities,
            self.costs,
            self.best_cost,
            self.best_bitstring,
        ) = self.run_simulation(self.register, self.drive, QUBO, convert_to_tensor=True)

    if self.bitstrings is None or self.counts is None:
        # TODO: what needs to be returned here?
        # the generate function should always return a drive - even if it is not good.
        # we need to return a drive (self.drive) - which is none here.
        # return self.drive, QUBOSolution(None, None)
        raise RuntimeError("No solution found")

    assert self.costs is not None
    solution = QUBOSolution(
        bitstrings=self.bitstrings,
        counts=self.counts,
        probabilities=self.probabilities,
        costs=self.costs,
    )
    assert self.drive is not None
    return self.drive, solution

run_simulation(register, drive, QUBO, convert_to_tensor=True)

Run a quantum program using backend and returns a tuple of (bitstrings, counts, probabilities, costs, best cost, best bitstring).

PARAMETER	DESCRIPTION
register	register of quantum program. TYPE: Register
drive	drive to run on backend. TYPE: Drive
QUBO	Qubo coefficients. TYPE: Tensor
convert_to_tensor	Convert tuple components to tensors. Defaults to True. TYPE: bool DEFAULT: True

RETURNS	DESCRIPTION
tuple	tuple of (bitstrings, counts, probabilities, costs, best cost, best bitstring) TYPE: tuple

Source code in qubosolver/pipeline/drive.py

def run_simulation(
    self,
    register: Register,
    drive: Drive,
    QUBO: torch.Tensor,
    convert_to_tensor: bool = True,
) -> tuple:
    """Run a quantum program using backend and returns
        a tuple of (bitstrings, counts, probabilities, costs, best cost, best bitstring).

    Args:
        register (Register): register of quantum program.
        drive (Drive): drive to run on backend.
        QUBO (torch.Tensor): Qubo coefficients.
        convert_to_tensor (bool, optional): Convert tuple components to tensors.
            Defaults to True.

    Returns:
        tuple: tuple of (bitstrings, counts, probabilities, costs, best cost, best bitstring)
    """
    try:
        program = QuantumProgram(register=register, drive=drive)
        program.compile_to(
            self.device,
            profile=compiler_profile(self.config),
            device_max_duration_ratio=max_duration_ratio(self.config),
        )
        job = self.backend.run(program)
        bitstring_counts = job.results().final_bitstrings

        cost_dict = {b: self.compute_qubo_cost(b, QUBO) for b in bitstring_counts.keys()}

        best_bitstring = min(cost_dict, key=cost_dict.get)  # type: ignore[arg-type]
        best_cost = cost_dict[best_bitstring]

        if convert_to_tensor:
            keys = list(bitstring_counts.keys())
            values = list(bitstring_counts.values())

            bitstrings_tensor = torch.tensor(
                [[int(b) for b in bitstr] for bitstr in keys], dtype=torch.int32
            )
            counts_tensor = torch.tensor(values, dtype=torch.int32)
            probabilities_tensor = counts_tensor.float() / counts_tensor.sum()

            costs_tensor = torch.tensor(
                [self.compute_qubo_cost(b, QUBO) for b in keys], dtype=torch.float32
            )

            return (
                bitstrings_tensor,
                counts_tensor,
                probabilities_tensor,
                costs_tensor,
                best_cost,
                best_bitstring,
            )
        else:
            counts = list(bitstring_counts.values())
            nsamples = float(sum(counts))
            return (
                list(bitstring_counts.keys()),
                counts,
                [c / nsamples for c in counts],
                list(cost_dict.values()),
                best_cost,
                best_bitstring,
            )

    except Exception as e:
        print(f"Simulation failed: {e}")
        return (
            torch.tensor([]),
            torch.tensor([]),
            torch.tensor([]),
            torch.tensor([]),
            float("inf"),
            None,
        )

get_drive_shaper(instance, config, backend)

Method that returns the correct DriveShaper based on configuration. The correct drive shaping method can be identified using the config, and an object of this driveshaper can be returned using this function.

PARAMETER	DESCRIPTION
instance	The QUBO problem to embed. TYPE: QUBOInstance
config	The solver configuration used. TYPE: SolverConfig
backend	Backend to extract device from or to use during drive shaping. TYPE: Backend

RETURNS	DESCRIPTION
BaseDriveShaper	The representative Drive Shaper object.

Source code in qubosolver/pipeline/drive.py

def get_drive_shaper(
    instance: QUBOInstance,
    config: SolverConfig,
    backend: concepts.Backend,
) -> BaseDriveShaper:
    """
    Method that returns the correct DriveShaper based on configuration.
    The correct drive shaping method can be identified using the config, and an
    object of this driveshaper can be returned using this function.

    Args:
        instance (QUBOInstance): The QUBO problem to embed.
        config (SolverConfig): The solver configuration used.
        backend (Backend): Backend to extract device from or to use
            during drive shaping.

    Returns:
        (BaseDriveShaper): The representative Drive Shaper object.
    """
    if config.drive_shaping.drive_shaping_method == DriveType.HEURISTIC:
        return HeuristicDriveShaper(instance, config, backend)
    elif config.drive_shaping.drive_shaping_method == DriveType.OPTIMIZED:
        return OptimizedDriveShaper(instance, config, backend)
    elif issubclass(config.drive_shaping.drive_shaping_method, BaseDriveShaper):
        return cast(
            BaseDriveShaper,
            config.drive_shaping.drive_shaping_method(instance, config, backend),
        )
    else:
        raise NotImplementedError

Embedding

BLaDEmbedder(instance, config, backend)

Bases: BaseEmbedder

Atom-register embedder using the qoolqit BLaDe (Block-Layout and Degree-based) matrix-embedding algorithm.

BLaDe jointly optimises atom positions to match the logical adjacency structure of the QUBO graph with the physical Rydberg interaction matrix. Configuration is taken from config.embedding (BLaDe-specific fields: blade_steps_per_round, blade_starting_positions, blade_dimensions, min_distance).

Source code in qubosolver/pipeline/embedder.py

def __init__(self, instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend):
    """
    Args:
        instance (QUBOInstance): The QUBO problem to embed.
        config (SolverConfig): Solver configuration.
        backend (Backend): Execution backend providing device information.
    """
    self.instance: QUBOInstance = instance
    self.config: SolverConfig = config
    self.register: Register | None = None
    self.backend = backend

    # TODO: remove when bumping to qoolqit v1
    # for converting to qoolqit
    self._distance_conversion = self.config.device.converter.factors[2]

embed()

Run the BLaDe embedding algorithm and return the resulting register.

Reads embedding hyper-parameters from self.config.embedding, constructs a BladeConfig, runs Blade.embed on the QUBO coefficient matrix, optionally rescales coordinates to satisfy the min_distance constraint, and wraps the result as a Register. See Qoolqit's documentation (external) for details.

RETURNS	DESCRIPTION
Register	Atom register with positions optimised by BLaDe. TYPE: Register

Source code in qubosolver/pipeline/embedder.py

def embed(self) -> Register:
    """Run the BLaDe embedding algorithm and return the resulting register.

    Reads embedding hyper-parameters from ``self.config.embedding``,
    constructs a ``BladeConfig``, runs ``Blade.embed`` on the QUBO
    coefficient matrix, optionally rescales coordinates to satisfy the
    ``min_distance`` constraint, and wraps the result as a ``Register``.
    See [Qoolqit's documentation](https://pasqal-io.github.io/qoolqit/latest/reference/embedding/#qoolqit.embedding.BladeConfig) for details.


    Returns:
        Register: Atom register with positions optimised by BLaDe.
    """
    embed_config = self.config.embedding
    default = BladeConfig()
    step_per_round = embed_config.blade_steps_per_round
    if step_per_round is None:
        step_per_round = default.steps_per_round
    if embed_config.blade_starting_positions is not None:
        starting_positions = embed_config.blade_starting_positions.numpy()
    else:
        starting_positions = None

    min_distance = self.config.embedding.min_distance
    max_radial_distance = self.config.device.specs["max_radial_distance"]
    if min_distance is None or max_radial_distance is None:
        device = self.config.device
        max_min_dist_ratio = None
    else:
        device = None
        max_min_dist_ratio = max_radial_distance / min_distance

    config = BladeConfig(
        steps_per_round=step_per_round,
        starting_positions=starting_positions,
        dimensions=tuple(embed_config.blade_dimensions),
        max_min_dist_ratio=max_min_dist_ratio,
        device=device,
    )

    _blade = Blade(config)
    graph = _blade.embed(self.instance.coefficients.numpy())
    if min_distance is not None:
        graph.rescale_coords(spacing=min_distance)
    register = Register.from_graph(graph)

    return register

BaseEmbedder(instance, config, backend)

Bases: ABC

Abstract base class for all embedders.

Prepares the geometry (register) of atoms based on the QUBO instance and returns a Register compatible with Pasqal/Pulser devices.

ATTRIBUTE	DESCRIPTION
instance	The QUBO problem to embed. TYPE: QUBOInstance
config	Solver configuration including embedding settings. TYPE: SolverConfig
register	The generated register (set after embed). TYPE: Register | None
backend	The execution backend (used to access device specs). TYPE: Backend

Note

PARAMETER	DESCRIPTION
instance	The QUBO problem to embed. TYPE: QUBOInstance
config	Solver configuration. TYPE: SolverConfig
backend	Execution backend providing device information. TYPE: Backend

Source code in qubosolver/pipeline/embedder.py

def __init__(self, instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend):
    """
    Args:
        instance (QUBOInstance): The QUBO problem to embed.
        config (SolverConfig): Solver configuration.
        backend (Backend): Execution backend providing device information.
    """
    self.instance: QUBOInstance = instance
    self.config: SolverConfig = config
    self.register: Register | None = None
    self.backend = backend

    # TODO: remove when bumping to qoolqit v1
    # for converting to qoolqit
    self._distance_conversion = self.config.device.converter.factors[2]

embed() abstractmethod

Create a register (atom layout) for the QUBO instance.

RETURNS	DESCRIPTION
Register	The register. TYPE: Register

Source code in qubosolver/pipeline/embedder.py

@abstractmethod
def embed(self) -> Register:
    """Create a register (atom layout) for the QUBO instance.

    Returns:
        Register: The register.
    """
    ...

GreedyEmbedder(instance, config, backend)

Bases: BaseEmbedder

Create an embedding in a greedy fashion.

At each step, place one logical node onto one trap to minimize the incremental mismatch between the logical QUBO matrix Q and the physical interaction matrix U (approx. C / ||r_i - r_j||^6).

Source code in qubosolver/pipeline/embedder.py

def __init__(self, instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend):
    """
    Args:
        instance (QUBOInstance): The QUBO problem to embed.
        config (SolverConfig): Solver configuration.
        backend (Backend): Execution backend providing device information.
    """
    self.instance: QUBOInstance = instance
    self.config: SolverConfig = config
    self.register: Register | None = None
    self.backend = backend

    # TODO: remove when bumping to qoolqit v1
    # for converting to qoolqit
    self._distance_conversion = self.config.device.converter.factors[2]

embed()

Creates a layout of atoms as the register.

RETURNS	DESCRIPTION
Register	The register. TYPE: Register

Source code in qubosolver/pipeline/embedder.py

@typing.no_type_check
def embed(self) -> Register:
    """
    Creates a layout of atoms as the register.

    Returns:
        Register: The register.
    """
    if self.config.embedding.greedy_traps == -1:
        self.config.embedding.greedy_traps = self._number_of_traps_from_device(
            self.config.device
        )

    if self.config.embedding.greedy_traps < self.instance.size:
        raise ValueError(
            "Number of traps must be at least equal to the number of atoms on the register."
        )

    # compute density (unchanged)
    self.config.embedding.greedy_density = calculate_density(
        self.instance.coefficients, self.instance.size
    )

    # build params for the Greedy algorithm
    params = {
        "device": self.config.device._device,
        "layout": self.config.embedding.greedy_layout,
        "traps": int(self.config.embedding.greedy_traps),
        "spacing": float(self.config.embedding.greedy_spacing),
        # animation controls (all read by Greedy)
        "draw_steps": bool(self.config.embedding.draw_steps),  # collect per-step data
        "animation": bool(self.config.embedding.draw_steps),  # render animation after run
        "animation_save_path": self.config.embedding.animation_save_path,  # optional export
    }

    # --- DEBUG / INFO: show where Greedy comes from + the params we’ll pass
    dev = params["device"]
    dev_str = (
        getattr(dev, "name", None)
        or getattr(dev, "device_name", None)
        or dev.__class__.__name__
    )
    printable = dict(params)
    printable["device"] = dev_str  # avoid dumping the whole object
    # --- Call Greedy (unchanged public signature)
    best, _, coords, _, _ = Greedy().launch_greedy(
        Q=self.instance.coefficients,
        params=params,
        # no extra kwargs; Greedy reads animation/draw/save_path from params
    )
    min_distance = self.config.embedding.min_distance
    if min_distance is not None:
        min_reg_distance = torch.cdist(coords, coords).fill_diagonal_(float("inf")).min()
        coords *= min_distance / min_reg_distance
    else:
        coords /= self._distance_conversion

    # build the register (unchanged)
    qubits = {f"q{i}": coord for i, coord in enumerate(coords)}
    register = Register(qubits)
    return register

get_embedder(instance, config, backend)

Method that returns the correct embedder based on configuration. The correct embedding method can be identified using the config, and an object of this embedding can be returned using this function.

PARAMETER	DESCRIPTION
instance	The QUBO problem to embed. TYPE: QUBOInstance
config	The quantum device to target. TYPE: Device

RETURNS	DESCRIPTION
BaseEmbedder	The representative embedder object.

Source code in qubosolver/pipeline/embedder.py

def get_embedder(
    instance: QUBOInstance, config: SolverConfig, backend: concepts.Backend
) -> BaseEmbedder:
    """
    Method that returns the correct embedder based on configuration.
    The correct embedding method can be identified using the config, and an
    object of this embedding can be returned using this function.

    Args:
        instance (QUBOInstance): The QUBO problem to embed.
        config (Device): The quantum device to target.

    Returns:
        (BaseEmbedder): The representative embedder object.
    """

    if config.embedding.embedding_method == EmbedderType.BLADE:
        return BLaDEmbedder(instance, config, backend)
    elif config.embedding.embedding_method == EmbedderType.GREEDY:
        return GreedyEmbedder(instance, config, backend)
    elif issubclass(config.embedding.embedding_method, BaseEmbedder):
        return typing.cast(
            BaseEmbedder, config.embedding.embedding_method(instance, config, backend)
        )
    else:
        raise NotImplementedError