qat.mps.mpo.StateMPO

class qat.mps.mpo.StateMPO(tensor_list: list = None, tensor_types: list = None, external_dims: list = None)

MPO implementation :param tensor_list: list of tensors for internal MPS representation :type tensor_list: list(array) :param tensor_types: list of tensor types for internal MPS representation :type tensor_types: list(array) :param external_dims: the list of external dims (ket, bra) :type external_dims: list(pair(int)

contract(max_qubit_memory_limit: int = 12)

Contract the MPO into its statevector representation.

Parameters:

max_qubit_memory_limit (int, optional) – Limits the size of the MPO to be contracted to a specific number of qubit to avoid memory issues. Default to 12.

Returns:

The density matrix.

Return type:

np.ndarray

expectation_value(obs: Observable) → complex

Compute the expectation value of the Observable.

Parameters:

obs (Observable) – The observable to compute.

Returns:

Expectation value for given observable.

Return type:

complex

get_memory_used()

Compute memory used by the tensor network in megabytes (MB).

Returns:

Number of MB used

Return type:

float

load(filepath: str)

Load the MPO from an NPZ file.

Parameters:

filepath (str) – Path of the NPZ file.

sample(state_index: int) → float

Get probability of input state.

Parameters:

state_index (int) – State index LSB ordered (0 = |00…00>, 1 = |00…01>, …etc)

Returns:

Probability of the realisation of input state index.

Return type:

float

save(filepath: str)

Save the MPO to the disk as NumPy NPZ file.

Parameters:

filepath (str) – Path where the NPZ file will be saved.

trace() → complex

Compute trace of MPO.