qiskit.aqua.components.initial_states.Custom

class Custom(num_qubits, state='zero', state_vector=None, circuit=None)

The custom initial state.

A custom initial state can be created with this component. It allows a state to be defined in the form of custom probability distribution with the state_vector, or by providing a desired circuit to set the state.

Also state can be used having a few pre-defined initial states for convenience:

• ‘zero’: configures the state vector with the zero probability distribution, and is effectively equivalent to the Zero initial state.

• ‘uniform’: This setting configures the state vector with the uniform probability distribution. All the qubits are set in superposition, each of them being initialized with a Hadamard gate, which means that a measurement will have equal probabilities to become \(1\) or \(0\).

• ‘random’: This setting assigns the elements of the state vector according to a random probability distribution.

The custom initial state will be set from the circuit, the state_vector, or state, in that order. For state_vector the provided custom probability distribution will be internally normalized so the total probability represented is \(1.0\).

Parameters

• num_qubits (int) – Number of qubits, has a minimum value of 1.

• state (str) – Use a predefined state of (‘zero’ | ‘uniform’ | ‘random’)

• state_vector (Union[ndarray, StateFn, None]) – An optional vector of complex or float representing the state as a probability distribution which will be normalized to a total probability of 1 when initializing the qubits. The length of the vector must be \(2^q\), where \(q\) is the num_qubits value. When provided takes precedence over state.

• circuit (Optional[QuantumCircuit]) – A quantum circuit for the desired initial state. When provided takes precedence over both state_vector and state.

Raises

AquaError – invalid input

__init__(num_qubits, state='zero', state_vector=None, circuit=None)

Parameters

• num_qubits (int) – Number of qubits, has a minimum value of 1.

• state (str) – Use a predefined state of (‘zero’ | ‘uniform’ | ‘random’)

• state_vector (Union[ndarray, StateFn, None]) – An optional vector of complex or float representing the state as a probability distribution which will be normalized to a total probability of 1 when initializing the qubits. The length of the vector must be \(2^q\), where \(q\) is the num_qubits value. When provided takes precedence over state.

• circuit (Optional[QuantumCircuit]) – A quantum circuit for the desired initial state. When provided takes precedence over both state_vector and state.

Raises

AquaError – invalid input

Methods

__init__(num_qubits[, state, state_vector, …])	type num_qubits int
construct_circuit([mode, register])	Construct the statevector of desired initial state.

Attributes

bitstr

property bitstr

construct_circuit(mode='circuit', register=None)

Construct the statevector of desired initial state.

Parameters

• mode – vector or circuit. The vector mode produces the vector. While the circuit constructs the quantum circuit corresponding that vector.

• register – qubits for circuit construction.

Returns

statevector.

Return type

QuantumCircuit or numpy.ndarray

Raises

AquaError – when mode is not ‘vector’ or ‘circuit’.