PhaseEstimation¶

class
PhaseEstimation
(num_evaluation_qubits, unitary, iqft=None, name='QPE')[source]¶ Bases:
qiskit.circuit.quantumcircuit.QuantumCircuit
Phase Estimation circuit.
In the Quantum Phase Estimation (QPE) algorithm [1, 2, 3], the Phase Estimation circuit is used to estimate the phase \(\phi\) of an eigenvalue \(e^{2\pi i\phi}\) of a unitary operator \(U\), provided with the corresponding eigenstate \(psi\rangle\). That is
\[U\psi\rangle = e^{2\pi i\phi} \psi\rangle\]This estimation (and thereby this circuit) is a central routine to several wellknown algorithms, such as Shor’s algorithm or Quantum Amplitude Estimation.
References:
 [1]: Kitaev, A. Y. (1995). Quantum measurements and the Abelian Stabilizer Problem. 1–22.
 [2]: Michael A. Nielsen and Isaac L. Chuang. 2011.
Quantum Computation and Quantum Information: 10th Anniversary Edition (10th ed.). Cambridge University Press, New York, NY, USA.
 [3]: Qiskit
 Parameters
num_evaluation_qubits (
int
) – The number of evaluation qubits.unitary (
QuantumCircuit
) – The unitary operation \(U\) which will be repeated and controlled.iqft (
Optional
[QuantumCircuit
]) – A inverse Quantum Fourier Transform, per default the inverse ofQFT
is used. Note that the QFT should not include the usual swaps!name (
str
) – The name of the circuit.
Note
The inverse QFT should not include a swap of the qubit order.
 Reference Circuit:
Attributes

ancillas
¶ Returns a list of ancilla bits in the order that the registers were added.

calibrations
¶ Return calibration dictionary.
 The custom pulse definition of a given gate is of the form
{‘gate_name’: {(qubits, params): schedule}}

clbits
¶ Returns a list of classical bits in the order that the registers were added.

data
¶ Return the circuit data (instructions and context).
 Returns
a listlike object containing the tuples for the circuit’s data.
Each tuple is in the format
(instruction, qargs, cargs)
, where instruction is an Instruction (or subclass) object, qargs is a list of Qubit objects, and cargs is a list of Clbit objects. Return type
QuantumCircuitData

extension_lib
= 'include "qelib1.inc";'¶

global_phase
¶ Return the global phase of the circuit in radians.

header
= 'OPENQASM 2.0;'¶

instances
= 16¶

metadata
¶ The user provided metadata associated with the circuit
The metadata for the circuit is a user provided
dict
of metadata for the circuit. It will not be used to influence the execution or operation of the circuit, but it is expected to be passed between all transforms of the circuit (ie transpilation) and that providers will associate any circuit metadata with the results it returns from execution of that circuit.

num_ancillas
¶ Return the number of ancilla qubits.

num_clbits
¶ Return number of classical bits.

num_parameters
¶ Convenience function to get the number of parameter objects in the circuit.

num_qubits
¶ Return number of qubits.

parameters
¶ Convenience function to get the parameters defined in the parameter table.

prefix
= 'circuit'¶

qubits
¶ Returns a list of quantum bits in the order that the registers were added.