DensityMatrix

class DensityMatrix(data, dims=None)

DensityMatrix class

Initialize a density matrix object.

Parameters

• data (matrix_like or vector_like) – a density matrix or statevector. If a vector the density matrix is constructed as the projector of that vector.

• dims (int or tuple or list) – Optional. The subsystem dimension of the state (See additional information).

Raises

QiskitError – if input data is not valid.

Additional Information:

The dims kwarg can be None, an integer, or an iterable of integers.

• Iterable – the subsystem dimensions are the values in the list with the total number of subsystems given by the length of the list.

• Int or None – the leading dimension of the input matrix specifies the total dimension of the density matrix. If it is a power of two the state will be initialized as an N-qubit state. If it is not a power of two the state will have a single d-dimensional subsystem.

Attributes

DensityMatrix.atol	The absolute tolerance parameter for float comparisons.
DensityMatrix.data	Return data.
DensityMatrix.dim	Return total state dimension.
DensityMatrix.num_qubits	Return the number of qubits if a N-qubit state or None otherwise.
DensityMatrix.rtol	The relative tolerance parameter for float comparisons.

Methods

DensityMatrix.__mul__(other)
DensityMatrix.add(other)	Return the linear combination self + other.
DensityMatrix.conjugate()	Return the conjugate of the density matrix.
DensityMatrix.copy()	Make a copy of current operator.
DensityMatrix.dims([qargs])	Return tuple of input dimension for specified subsystems.
DensityMatrix.evolve(other[, qargs])	Evolve a quantum state by an operator.
DensityMatrix.expand(other)	Return the tensor product state other ⊗ self.
DensityMatrix.from_instruction(instruction)	Return the output density matrix of an instruction.
DensityMatrix.from_int(i, dims)	Return a computational basis state density matrix.
DensityMatrix.from_label(label)	Return a tensor product of Pauli X,Y,Z eigenstates.
DensityMatrix.is_valid([atol, rtol])	Return True if trace 1 and positive semidefinite.
DensityMatrix.measure([qargs])	Measure subsystems and return outcome and post-measure state.
DensityMatrix.multiply(other)	Return the scalar multipled state other * self.
DensityMatrix.probabilities([qargs, decimals])	Return the subsystem measurement probability vector.
DensityMatrix.probabilities_dict([qargs, …])	Return the subsystem measurement probability dictionary.
DensityMatrix.purity()	Return the purity of the quantum state.
DensityMatrix.reset([qargs])	Reset state or subsystems to the 0-state.
DensityMatrix.sample_counts(shots[, qargs])	Sample a dict of qubit measurement outcomes in the computational basis.
DensityMatrix.sample_memory(shots[, qargs])	Sample a list of qubit measurement outcomes in the computational basis.
DensityMatrix.seed([value])	Set the seed for the quantum state RNG.
DensityMatrix.set_atol(value)	Set the class default absolute tolerance parameter for float comparisons.
DensityMatrix.set_rtol(value)	Set the class default relative tolerance parameter for float comparisons.
DensityMatrix.subtract(other)	Return the linear operator self - other.
DensityMatrix.tensor(other)	Return the tensor product state self ⊗ other.
DensityMatrix.to_counts()	Returns the density matrix as a counts dict of probabilities.
DensityMatrix.to_dict([decimals])	Convert the density matrix to dictionary form.
DensityMatrix.to_operator()	Convert to Operator
DensityMatrix.trace()	Return the trace of the density matrix.
DensityMatrix.__mul__(other)