Creating Physical Noise Models

Noise Mechanisms currently supported

The current version of the HQS Noise App supports single-qubit physical noise in the form of damping, dephasing, and depolarisation, with user-given decoherence rates. We assume that the noise is the same for all gate types.

Setting up the HQS Noise App

The HQS Noise App has no parameters for initialization.

However, there are some settings that have default values and can be set with setter functions with the same name as the setting.

• number_measurements : The number of projective measurements used when measuring observables (defaults to 100000).
• use_bath_as_control: True/False to use/not use bath qubits as control when solving system-bath problems (defaults to False).
• algorithm : Options are: ParityBased, QSWAP, QSWAPMolmerSorensen, VariableMolmerSorensen, (defaults to ParityBased).
• noise_symmetrization : Whether or not to apply noise symmetrization, which controls whether the Trotterstep is symmetrized with respect to damping noise. When the overall noise has the tendency to favor one state (|0> or |1>), the Trotterstep can be symmetrized by doubling the Trotter circuit and flipping the definition of |0> and |1> for the second circuit. This process will bring the effective noise closer to a balanced noise at the cost of larger decoherence overall. This option defaults to false.
• trotterization_order : Trotterization order of time-evolution operator, 1 or 2 (defaults to 1)
• parallelization_blocks : The way noise is added to a quantum circuit. By default, this is set to false, so the noise will be inserted on all qubits, according to the user-specified NoiseModels (see the section on Creating a noise model, below). If the parallelization_blocks option is set to true, the noise mode is changed to ParallelizationBlocks. In this case, the noise model adds noise on the qubits that are involved in a block or parallel operations. These noise terms are added after a PragmaStopParallelBlock, which signals the end of the parallel operations in a qoqo circuit.

Creating a Device

We can define an AllToAllDevice device with the following settings:

• number_of_qubits : The number of qubits for the device.
• single_qubit_gates : The list of single-qubit gates available on the quantum computer.
• two_qubit_gates : The list of two-qubit gates available on the quantum computer.
• default_gate_time : The default gate time of the specified gates.

The single_qubit_gates option can be any list of single qubit gates available in the HQS qoqo library as long as it contains one of the following combinations:

• RotateX and RotateZ
• RotateY and RotateZ
• RotateX and RotateY
• RotateZ and SqrtPauliX and InvSqrtPauliX

The supported options for two_qubit_gates are:

• CNOT
• ControlledPauliZ
• ControlledPhaseShift
• MolmerSorensenXX
• VariableMSXX

An example code for setting device information is given below.

from qoqo import devices

# Setting up the device.
number_of_qubits=5
single_qubit_gates = ["RotateX", "RotateZ", "RotateY"]
two_qubit_gates = ["CNOT"]
default_gate_time = 1.0
device = devices.AllToAllDevice(
    number_of_qubits, single_qubit_gates, two_qubit_gates, default_gate_time
)

Creating a Noise Model

We can define a ContinuousDecoherenceModel noise model with the following types of noise:

• dephasing: Using the add_dephasing_rate function.
• depolarisation: Using the add_depolarising_rate function.
• damping: Using the add_damping_rate function.
• excitations: Using the add_excitation_rate function.

Each of these functions takes a list of qubits to apply the noise to and a noise rate (float), and returns the modified ContinuousDecoherenceModel. An example code of setting noise model information, including the damping of qubits, reads as follows.

from qoqo import noise_models

# Setting up the noise model.
damping = 1e-3
dephasing = 5e-4
noise_model = (
    noise_models.ContinuousDecoherenceModel()
    .add_damping_rate([0, 1, 2], damping)
    .add_dephasing_rate([3, 4], dephasing)
)