DensityMatrix¶

class DensityMatrix(data, dims=None)[source]¶

Bases: qiskit.quantum_info.states.quantum_state.QuantumState, qiskit.quantum_info.operators.mixins.tolerances.TolerancesMixin

DensityMatrix class

Initialize a density matrix object.

Parameters

(np.ndarray or list or matrix_like or QuantumCircuit or (data) – qiskit.circuit.Instruction): A statevector, quantum instruction or an object with a to_operator or to_matrix method from which the density matrix can be constructed. If a vector the density matrix is constructed as the projector of that vector. If a quantum instruction, the density matrix is constructed by assuming all qubits are initialized in the zero state.
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.

Methods

`conjugate`	Return the conjugate of the density matrix.
`copy`	Make a copy of current operator.
`dims`	Return tuple of input dimension for specified subsystems.
`draw`	Return a visualization of the Statevector.
`evolve`	Evolve a quantum state by an operator.
`expand`	Return the tensor product state other ⊗ self.
`expectation_value`	Compute the expectation value of an operator.
`from_instruction`	Return the output density matrix of an instruction.
`from_int`	Return a computational basis state density matrix.
`from_label`	Return a tensor product of Pauli X,Y,Z eigenstates.
`is_valid`	Return True if trace 1 and positive semidefinite.
`measure`	Measure subsystems and return outcome and post-measure state.
`probabilities`	Return the subsystem measurement probability vector.
`probabilities_dict`	Return the subsystem measurement probability dictionary.
`purity`	Return the purity of the quantum state.
`reset`	Reset state or subsystems to the 0-state.
`reverse_qargs`	Return a DensityMatrix with reversed subsystem ordering.
`sample_counts`	Sample a dict of qubit measurement outcomes in the computational basis.
`sample_memory`	Sample a list of qubit measurement outcomes in the computational basis.
`seed`	Set the seed for the quantum state RNG.
`tensor`	Return the tensor product state self ⊗ other.
`to_dict`	Convert the density matrix to dictionary form.
`to_operator`	Convert to Operator
`to_statevector`	Return a statevector from a pure density matrix.
`trace`	Return the trace of the density matrix.

Attributes

num_qubits¶: Return the number of qubits if a N-qubit state or None otherwise.