Parameters¶

Overview¶

QuantumRingsLib supports parameterized quantum circuits (PQCs). In a parameterized circuit, gate arguments can be defined using symbols and later assigned concrete values before execution.

This page shows:

how to create parameters (Parameter and ParameterVector)
how to use them in a QuantumCircuit
how to assign values using QuantumCircuit.assign_parameters(...)

For the end-to-end workflow (provider → backend → circuit → run), see Circuits.

Parameter objects¶

Named parameters¶

Use Parameter(name) to create a named symbolic parameter.

from QuantumRingsLib import Parameter

theta = Parameter("theta")

Parameter vectors¶

Use ParameterVector(name, length) to create a vector of named parameters. Access individual parameters using subscripts (myparamvec[i]).

from QuantumRingsLib import ParameterVector

myparamvec = ParameterVector("test", 6)
# Example: test[0], test[1], ... test[5]
p0 = myparamvec[0]

Using parameters in a circuit¶

Parameters can be used as arguments to parameterized gates.

import math
from QuantumRingsLib import QuantumRegister, ClassicalRegister, QuantumCircuit
from QuantumRingsLib import Parameter, ParameterVector

q = QuantumRegister(5, "q")
c = ClassicalRegister(5, "c")
qc = QuantumCircuit(q, c)

myparamvec = ParameterVector("test", 6)
theta = Parameter("theta")
phi = Parameter("phi")

qc.h(q[0])
qc.mcp(theta, [q[0], q[1], q[3]], q[2])
qc.rx(phi, 3)
qc.rz(myparamvec[5], 0)
qc.u(myparamvec[0], myparamvec[1], myparamvec[2], 1)

Assigning values¶

Use qc.assign_parameters(dict_parameters, inplace=...) to replace symbolic parameters with numeric values.

Quantum Rings documentation notes:

all required parameter values must be provided together in a single dictionary
if inplace is True, the existing circuit is updated
if inplace is False, a circuit with applied parameters is returned

Example:

import math

values = {
    "test[0]": math.pi,
    "test[1]": math.pi / 2,
    "test[2]": math.pi / 3,
    "test[5]": math.pi / 7,
    "theta":   math.pi / 8,
    "phi":     math.pi / 9,
}

qc.assign_parameters(values, inplace=True)

After assignment, the circuit can be executed using the same workflow as any other circuit. See Circuits.

Notes¶

The QuantumCircuit.assign_parameters(...) API also includes flat_input and strict parameters in its signature; Quantum Rings documentation describes these as unused.
QuantumCircuit.num_parameters exists but is documented as “currently not used”.