paddle_quantum.state.state

The basic class of the quantum state.

class paddle_quantum.state.state.State(data, num_qubits=None, backend=None, dtype=None, override=False)

Bases: object

The quantum state class.

Parameters:

  • data (Tensor | ndarray | QEnv) – The mathematical analysis of quantum state.

  • num_qubits (int | None) – The number of qubits contained in the quantum state. Defaults to None, which means it will be inferred by the data.

  • backend (Backend | None) – Used to specify the backend used. Defaults to None, which means to use the default backend.

  • dtype (str | None) – Used to specify the data dtype of the data. Defaults to None, which means to use the default data type.

  • override (bool | None) – whether override the input test. ONLY for internal use. Defaults to False.

Raises:

ValueError – Cannot recognize the backend.

property ket: Tensor

Return the ket form in state_vector backend

Raises:

ValueError – the backend must be in StateVector

Returns:

ket form of the state

property bra: Tensor

Return the bra form in state_vector backend

Raises:

ValueError – the backend must be in StateVector

Returns:

bra form of the state

normalize()

Normalize this state

Raises:

NotImplementedError – does not support normalization for the backend

evolve(H, t)

Evolve the state under the Hamiltonian H i.e. apply unitary operator \(e^{-itH}\)

Parameters:

  • H (ndarray | Tensor | Hamiltonian) – the Hamiltonian of the system

  • t (float) – the evolution time

Raises:

NotImplementedError – does not support evolution for the backend

kron(other)

Kronecker product between states

Parameters:

other (State) – a quantum state

Returns:

the tensor product of these two states

Return type:

State

numpy()

Get the data in numpy.

Returns:

The numpy array of the data for the quantum state.

Return type:

ndarray

to(backend, dtype=None, device=None, blocking=None)

Change the property of the state.

Parameters:

  • backend (str) – Specify the new backend of the state.

  • dtype (str | None) – Specify the new data type of the state.

  • device (str | None) – Specify the new device of the state.

  • blocking (str | None) – Specify the new blocking of the state.

Raises

NotImplementedError: only support transformation between StateVector and DensityMatrix NotImplementedError: Transformation for device or blocking is not supported.

clone()

Return a copy of the quantum state.

Returns:

A new state which is identical to this state.

Return type:

State

property oper_history: List[Dict[str, str | List[int] | Tensor]]

The operator history stored for the QPU backend

Raises:

  • NotImplementedError – This property should be called for the backend quleaf only.

  • ValueError – This state does not have operator history: run the circuit first.

expec_val(hamiltonian, shots=0)

The expectation value of the observable with respect to the quantum state.

Parameters:

  • hamiltonian (Hamiltonian) – Input observable.

  • shots (int | None) – Number of measurement shots.

Raises:

NotImplementedError – If the backend is wrong or not implemented.

Returns:

The expectation value of the input observable for the quantum state.

Return type:

float

measure(shots=0, qubits_idx=None, plot=False, record=False)

Measure the quantum state

Parameters:

  • shots (int | None) – the number of measurements on the quantum state output by the quantum circuit. Default is 0, which means the exact probability distribution of measurement results are returned.

  • qubits_idx (Iterable[int] | int | None) – The index of the qubit to be measured. Defaults to None, which means all qubits are measured.

  • plot (bool | None) – Whether to draw the measurement result plot. Defaults to False which means no plot.

  • record (bool | None) – Whether to return the original measurement record. Defaults to False which means no record.

Raises:

  • ValueError – The number of shots should be greater than 0.

  • NotImplementedError – When the backend is Quleaf, record is not supprted .

  • NotImplementedError – If the backend is wrong or not implemented.

  • NotImplementedError – The qubit index is wrong or not supported.

  • ValueError – Returning records requires the number of shots to be greater than 0.

Returns:

Measurement results

Return type:

dict

reset_sequence(target_sequence=None)

reset the qubit order to a given sequence

Parameters:

target_sequence (List[int] | None) – target sequence. Defaults to None.

Returns:

state with given qubit order

Return type:

State