# DensityMatrix¶

class DensityMatrix(data, dims=None)[Quellcode]

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

DensityMatrix class

Initialize a density matrix object.

Parameter
• (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).

Verursacht

QiskitError – if input data is not valid.

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

atol = 1e-08
data

Return data.

dim

num_qubits
rtol = 1e-05