Noise models

QB Qristal has built-in noise models that are useful for:

• Emulating the noise inherent in hardware quantum gates, and

• Optimizing qubit assignment for a given quantum circuit.

For details on the simulators that support these noise models, please see this link.

Summary of built-in noise models

default

Model name	default
Total # qubits	User defined
Fully connected degree	All-to-all
Fidelity of 2-qubit gate	99.9%
Fidelity of 1-qubit gate	99.9%
Readout error p(0|1)	0.01
Readout error p(1|0)	0.01
QObj generator	“xacc-qobj”
Basis gate set	u1, u2, u3, cx

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

This model takes the number of qubits specified by the user and generates a fully connected topology between all qubits. Quantum gate noise is modelled using single-qubit depolarization and 2-qubit depolarization channels. The channels are uniform across all qubits. Readout errors are also accounted for in this model.

qb-nm1

Model name	qb-nm1
QObj generator	“qristal-qobj”
Basis gate set	rx, ry, cz

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

qb-nm2

Model name	qb-nm2
QObj generator	“qristal-qobj”
Basis gate set	rx, ry, cz

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

qb-nm3

Model name	qb-nm3
QObj generator	“qristal-qobj”
Basis gate set	rx, ry, cz

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

qb-qdk1

Model name	qb-qdk1
QObj generator	“qristal-qobj”
Basis gate set	rx, ry, cz

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

qb-dqc2

Model name	qb-dqc2
QObj generator	“qristal-qobj”
Basis gate set	rx, ry, cz

This model is applicable to:

• Open source releases: 2023 onwards

• Commercial emulator releases: 2023 onwards

Examples showing the use of a built-in noise model

C++

This example can be found at examples/cpp/noise_model, along with a CMakeLists.txt file for building it.

#include "qb/core/session.hpp"
int main(int argc, char * argv[])
{
    auto my_sim = qb::session();
    my_sim.qb12();          // Set up meaningful defaults
    my_sim.set_qn(2);       // 2 qubits
    my_sim.set_acc("aer");  // Aer simulator selected
    my_sim.set_noise(true); // Set this to true for noise models to be active
    my_sim.set_noise_model("default"); // Also available from the Qristal Emulator: "qb-nm1" , "qb-nm2" , "qb-qdk1"
    my_sim.set_instring(R"(
       OPENQASM 2.0;
       include "qelib1.inc";
       creg c[2];
       h q[0];
       cx q[0],q[1];
       measure q[1] -> c[1];
       measure q[0] -> c[0];
       )");
    my_sim.run();
    std::string result = ((my_sim.get_out_raws()).at(0)).at(0);
    std::cout << result << std::endl;
    return 0;
}

Python

This example can be found at examples/python/noise_model.py.

import qb.core
my_sim = qb.core.session()
my_sim.qb12()
my_sim.qn = 2
my_sim.acc = "aer"
my_sim.noise = True
my_sim.noise_model = "default"
my_sim.instring = '''
    OPENQASM 2.0;
    include "qelib1.inc";
    creg c[2];
    h q[0];
    cx q[0],q[1];
    measure q[1] -> c[1];
    measure q[0] -> c[0];
'''
my_sim.run()
print(my_sim.out_raws[0])

User defined noise models

QB Qristal allows an end-user to implement noise models. First use NoiseProperties to set up noise model parameters. Then pass the parameters to the constructor of qb::NoiseModel.

Modifying the default noise model

See the source code for the default noise model [DefaultNoiseModelFactory] in:

core/src/noise_model/noise_model_factory.cpp

See the constructor [NoiseModel::NoiseModel(const NoiseProperties &noise_props)] in:

core/src/noise_model/noise_model.cpp

Noise channels

Name	Description
amplitude_damp	Amplitude damping with parameter \(\gamma\)
phase_damp	Phase damping with parameter \(\gamma\)
depolarize	Single-qubit and two-qubit depolarization with probability \(p\)
generalized_phase_amplitude_damp	Generalized amplitude and phase damping with 3 parameters: excited state population, amplitude damping, phase damping
generalized_amplitude_damp	Generalized amplitude damping with 2 parameters: excited state population, gamma

See the header code in:

core/include/qb/core/noise_model/noise_model.hpp