# qml.BasisState¶

class BasisState(n, wires)[source]

Prepares a single computational basis state.

Details:

• Number of wires: Any (the operation can act on any number of wires)

• Number of parameters: 1

• Gradient recipe: None (integer parameters not supported)

Note

If the BasisState operation is not supported natively on the target device, PennyLane will attempt to decompose the operation into PauliX operations.

Parameters
• n (array) – prepares the basis state $$\ket{n}$$, where n is an array of integers from the set $$\{0, 1\}$$, i.e., if n = np.array([0, 1, 0]), prepares the state $$|010\rangle$$.

• wires (Sequence[int] or int) – the wire(s) the operation acts on

 base_name Get base name of the operator. do_check_domain generator Generator of the operation. grad_method grad_recipe inverse Boolean determining if the inverse of the operation was requested. matrix Matrix representation of an instantiated operator in the computational basis. name Get and set the name of the operator. num_params num_wires par_domain parameters Current parameter values. string_for_inverse wires Wire values.
base_name

Get base name of the operator.

do_check_domain = True
generator

Generator of the operation.

A length-2 list [generator, scaling_factor], where

• generator is an existing PennyLane operation class or $$2\times 2$$ Hermitian array that acts as the generator of the current operation

• scaling_factor represents a scaling factor applied to the generator operation

For example, if $$U(\theta)=e^{i0.7\theta \sigma_x}$$, then $$\sigma_x$$, with scaling factor $$s$$, is the generator of operator $$U(\theta)$$:

generator = [PauliX, 0.7]


Default is [None, 1], indicating the operation has no generator.

grad_method = None
grad_recipe = None
inverse

Boolean determining if the inverse of the operation was requested.

matrix

Matrix representation of an instantiated operator in the computational basis.

Example:

>>> U = qml.RY(0.5, wires=1)
>>> U.matrix
>>> array([[ 0.96891242+0.j, -0.24740396+0.j],
[ 0.24740396+0.j,  0.96891242+0.j]])

Returns

matrix representation

Return type

array

name

Get and set the name of the operator.

num_params = 1
num_wires = -1
par_domain = 'A'
parameters

Current parameter values.

Fixed parameters are returned as is, free parameters represented by VariableRef instances are replaced by their current numerical value.

Returns

parameter values

Return type

list[Any]

string_for_inverse = '.inv'
wires

Wire values.

Returns

wire values

Return type

tuple[int]

 check_domain(p[, flattened]) Check the validity of a parameter. decomposition(n, wires) Returns a template decomposing the operation into other quantum operations. Multiplier and shift for the given parameter, based on its gradient recipe. Inverts the operation, such that the inverse will be used for the computations by the specific device. Append the operator to a BaseQNode queue.
check_domain(p, flattened=False)

Check the validity of a parameter.

VariableRef instances can represent any real scalars (but not arrays).

Parameters
• p (Number, array, VariableRef) – parameter to check

• flattened (bool) – True means p is an element of a flattened parameter sequence (affects the handling of ‘A’ parameters)

Raises
• TypeError – parameter is not an element of the expected domain

• ValueError – parameter is an element of an unknown domain

Returns

p

Return type

Number, array, VariableRef

static decomposition(n, wires)[source]

Returns a template decomposing the operation into other quantum operations.

get_parameter_shift(idx)

Multiplier and shift for the given parameter, based on its gradient recipe.

Parameters

idx (int) – parameter index

Returns

multiplier, shift

Return type

float, float

inv()

Inverts the operation, such that the inverse will be used for the computations by the specific device.

This method concatenates a string to the name of the operation, to indicate that the inverse will be used for computations.

Any subsequent call of this method will toggle between the original operation and the inverse of the operation.

Returns

operation to be inverted

Return type

Operator

queue()

Append the operator to a BaseQNode queue.