Simulation types

Every run is simulated by Maestro. MaestroBackend picks Maestro’s simulation type for each run from the noise in it, unless you pick one yourself.

How the type is picked

With the default simulation_type=None:

Run	Maestro simulation type
'pauli' (rate overrides included) or 'none'	Stabilizer, sampled on Pauli frames
any run with t1= but no coherent noise	Stabilizer, shot by shot (T1 decay is not a Pauli channel)
'coherent' or 'full'	MatrixProductState
any run, with simulation_type= set	that simulation type

Pauli frames sample a Clifford circuit with Pauli noise as fast as Stim does (see Performance). Coherent over-rotations, which no Clifford simulator can run, need the matrix product state (MPS), whose bond dimension has to be checked: see Bond dimension.

config_for returns the maestro.SimulatorConfig a run uses, so its simulation_type says which type that is:

from deltakit_maestro import MaestroBackend

backend = MaestroBackend()
backend.config_for('pauli').simulation_type                 # SimulationType.Stabilizer
backend.config_for('pauli', t1=1e-3).simulation_type        # SimulationType.Stabilizer
backend.config_for('coherent').simulation_type              # SimulationType.MatrixProductState
backend.config_for('coherent', coherent=0).simulation_type  # SimulationType.Stabilizer

config_for doesn’t see the circuit. For 'coherent' and 'full' the coherent strength is the coherent= keyword, else p_2q=. Without either, the strength is the circuit’s two-qubit gate noise, which config_for can’t know, so it takes it to be nonzero and answers MatrixProductState. The sampler knows the circuit and decides exactly.

Picking the type yourself

Pass a maestro.SimulationType to run everything with it, Pauli runs included:

import maestro

mps = MaestroBackend(
    simulation_type=maestro.SimulationType.MatrixProductState,
    max_bond_dimension=64,
)

That is how the noiseless check tests the bond dimension. The simulation type also changes how T1 decay runs: DensityMatrix and MatrixProductOperator apply amplitude damping, and every other type resets the qubit to |0⟩ (see The decoder’s detector error model).

The type is pinned

The type that runs is pinned (fixed_backend=True). Unpinned, Maestro samples any Clifford circuit on Pauli frames whatever the type, so an MPS run of a Pauli circuit would never touch the MPS. Pass fixed_backend=False to allow that:

MaestroBackend(simulation_type=maestro.SimulationType.MatrixProductState, fixed_backend=False)

A pinned Stabilizer still uses Pauli frames.

Other simulator options

MaestroBackend takes any other maestro.SimulatorConfig field as a keyword argument, such as:

• simulator_type=maestro.SimulatorType.Gpu to run on your GPU (get GPU access);

• max_simulators= to cap the threads one sampler uses.

The exception is seed, which simulate and compile_sampler take instead (see Seeds). The fields are checked when the backend is created, so a misspelt one raises TypeError at once.