Network Nodes¶

A quantum network is constructed from a collection of quantum devices serving as nodes in the network. Each network node operates on its local set of qubits. Each node’s operation can be conditioned upon both classical inputs and the measurement results of other nodes in the network.

class qnetvo.NetworkNode(num_in=1, num_out=1, wires=[], cc_wires_in=[], cc_wires_out=[], ansatz_fn=None, num_settings=0)[source]¶

A quantum network node.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
num_out (int) – The number of classical outputs for the node.
wires (list[int]) – The wires on which the node operates.
cc_wires_in (list[int]) – The classical communication wires input to the node.
cc_wires_out (list[int]) – The classical communication wires to output measurement results on.
ansatz_fn (function) – A PennyLane quantum circuit function called either as circuit(settings, wires), or as circuit(settings, wires, cc_wires) where settings is an array[float] of length num_settings and cc_wires contains the measurement results received from upstream nodes.
num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

Returns:

An instance of the NetworkNode class.

Calling a Network Node’s Ansatz Function:

Given an instantiated network node, node = NetworkNode(*args), its ansatz quantum circuit functtion can be called as node(settings, cc_wires) or, if node.cc_wires_in==[], the node can be called as node(settings) provided that cc_wires=[].

Attributes:

All inputs are stored as class attributes under the same name, e.g., the num_in argument is stored as node.num_in.

Network nodes are categorized by their function:

Prepare Node: Initializes a quantum state on the local qubits.
Processing Node: Applies an operation to its local qubits.
Noise Node: Applies noise to the local qubits.
Measure Node: Measures local qubits and outputs a classical value.
CC Sender Node: Measures local qubits and sends the result to classical communication (CC) receiver nodes.
CC Receiver Node: Applies an operation to its local qubits conditioned upon receieved classical data.

Prepare Nodes¶

class qnetvo.PrepareNode(num_in=1, wires=[], ansatz_fn=None, num_settings=0)[source]¶

A network node that initializes a state on its local qubit wires where the preparation can be conditioned on a classical input or upstream measurement results.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
wires (list[int]) – The wires on which the node operates.

ansatz_fn (function) –

A PennyLane quantum circuit function that takes the following form:

def prepare_ansatz(settings, wires):
    # initalize quantum state from |0...0>
    qml.ArbitraryStatePreparation(settings[0:6], wires=wires[0:2])

where settings is an array[float] of length num_settings.

num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

All attributes are inherited from the qnetvo.NetworkNode class.

Returns:: An instantiated PrepareNode class.

Processing Nodes¶

class qnetvo.ProcessingNode(num_in=1, wires=[], ansatz_fn=None, num_settings=0)[source]¶

A network node that operates upon its local qubit wires where the operation can be conditioned upon a classical input or upstream measurement results.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
wires (list[int]) – The wires on which the node operates.

ansatz_fn (function) –

A PennyLane quantum circuit function that takes the following form:

def processing_ansatz(settings, wires):
    # apply processing operation
    qml.ArbitraryUnitary(settings[0:16], wires=wires[0:2])

where settings is an array[float] of length num_settings.

num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

All attributes are inherited from the qnetvo.NetworkNode class.

Returns:: An instantiated ProcessingNode class.

Measure Nodes¶

class qnetvo.MeasureNode(num_in=1, num_out=1, wires=[], ansatz_fn=None, num_settings=0)[source]¶

A network node that measures its local qubit wires where the measurement can be conditioned on a classical input or upstream measurement results.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
num_out (int) – The number of classical outputs for the node.
wires (list[int]) – The wires on which the node operates.
ansatz_fn (function) –
A PennyLane quantum circuit function that takes the following form:
```
def measure_ansatz(settings, wires):
    # rotate measurement basis
    qml.Rot(*settings[0:3], wires=wires[0])
```
where settings is an array[float] of length num_settings. Note that the measurement ansatz does not apply a measurement operation. Measurement operations are specified later when qnetvo.NetworkAnsatz class is used to construct qnodes and cost functions.
num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

All attributes are inherited from the qnetvo.NetworkNode class. In addition, the number of classical outputs are specified.

Returns:: An instantiated MeasureNode class.

Classical Communication Nodes¶

class qnetvo.CCSenderNode(num_in=1, wires=[], cc_wires_out=[], ansatz_fn=None, num_settings=0)[source]¶

A network node that measures one or more of its local qubits and sends the measurement result(s) to one or more downstream qnetvo.CCReceiverNode instances.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
wires (list[int]) – The wires on which the node operates.
cc_wires_out (list[int]) – The classical communication wires to output measurement results on.

ansatz_fn (function) –

A PennyLane quantum circuit function that takes the following form:

def cc_sender_ansatz(settings, wires):
    # apply quantum circuit operations
    qml.Rot(*settings[0:3], wires=wires[0])

    # measure qubit to obtain classical communication bit
    cc_bit_out = qml.measure(wires[0])

    # output list of measurement results
    return [cc_bit_out]

where settings is an array[float] of length num_settings. Note that for each wire specified in cc_wires_out, there should be a corresponding cc_bit_out result obtained using qml.measure.

num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

All attributes are inherited from the qnetvo.NetworkNode class.

Returns:: An instantiated CCSenderNode class.

class qnetvo.CCReceiverNode(num_in=1, wires=[], cc_wires_in=[], ansatz_fn=None, num_settings=0)[source]¶

A network node that receives classical communication from an upstream qnetvo.CCSenderNode.

Parameters:

num_in (int) – The number of discrete classical inputs that the node accepts.
wires (list[int]) – The wires on which the node operates.
cc_wires_in (list[int]) – The classical communication wires input to the node.

ansatz_fn (function) –

A PennyLane quantum circuit function that takes the following form:

def cc_receive_ansatz(settings, wires, cc_wires):
    # apply quantum operations conditioned on classical communication
    qml.cond(cc_wires[0], qml.Rot)(*settings[0:3], wires=wires[0])
    qml.cond(cc_wires[1], qml.Rot)(*settings[3:6], wires=wires[0])

where settings is an array[float] of length num_settings and cc_wires contains the measurement results received from upstream nodes.

num_settings (int) – The number of settings parameterizing the ansatz_fn circuit.

All attributes are inherited from the qnetvo.NetworkNode class.

Note that the classical inputs specified by num_in are distinct from the classical communication inputs passed through cc_wires. That is, the classical inputs num_in are known before the network simulation is run whereas the classical communication in cc_wires are determined during the simulation.

Returns:: An instantiated CCReceiverNode class.

Noise Nodes¶

class qnetvo.NoiseNode(wires=[], ansatz_fn=None)[source]¶

A network node that applies noise to its local qubit wires.

Parameters:

wires (list[int) – The wires on which the node operates.
ansatz_fn (function) –
A PennyLane quantum circuit function <https://docs.pennylane.ai/en/stable/introduction/circuits.html> that takes the following form:
```
def noise_ansatz(settings, wires):
    # apply noise operation
    qml.Depolarizing(0.5, wires=wires[0])
    qml.AmplitudeDamping(0.5, wires=wires[1])
```
where settings=[] is unused because noise is considered to be static.

We model noise to be independent from classical inputs and upstream measurement results. Therefore, only the wires and ansatz_fn attributes can be set. All attributes are inherited from the qnetvo.NetworkNode class.

Returns:: An instantiated NoiseNode class.