compositeGate

Construct composite gate for quantum computing

Since R2023a

Installation Required: This functionality requires MATLAB Support Package for Quantum Computing.

Syntax

cg = compositeGate(circuit,targetQubits)

cg = compositeGate(gates,targetQubits)

cg = compositeGate(___,Name=name)

Description

cg = compositeGate(circuit,targetQubits) constructs a composite gate from an inner quantum circuit and returns a quantum.gate.CompositeGate object. The specified target qubits map each qubit of the inner circuit to a qubit of the outer circuit containing the composite gate.

The length of the targetQubits vector must be equal to the number of qubits in circuit. The Name property of circuit is copied to the Name property of cg.

cg = compositeGate(gates,targetQubits) constructs a composite gate from an array of inner gates. The specified target qubits map each qubit that the gates act on to a qubit of the outer circuit containing the composite gate.

The length of the targetQubits vector must be greater than or equal to the largest qubit index in gates.

cg = compositeGate(___,Name=name) sets the Name property of cg to name. You can use this option in addition to any of the input argument combinations in previous syntaxes.

Examples

Construct Composite Gate from Inner Circuit

Create a quantum circuit that consists of Hadamard and controlled NOT gates to entangle two qubits. Name the circuit as "bell".

innerGates = [hGate(1); cxGate(1,2)];
innerCircuit = quantumCircuit(innerGates,Name="bell")

innerCircuit = 

  quantumCircuit with properties:

    NumQubits: 2
        Gates: [2×1 quantum.gate.SimpleGate]
         Name: "bell"

Create an outer circuit that consists of two composite gates constructed from this inner "bell" circuit. The first composite gate acts on qubits 1 and 3 of the outer circuit containing this gate. The second composite gate acts on qubits 2 and 4 of the outer circuit containing this gate. The qubits of the inner circuit (qubits 1 and 2) are mapped to the qubits of the outer circuit (qubits 1 and 3 for the first composite gate, and qubits 2 and 4 for the second composite gate).

outerGates = [compositeGate(innerCircuit,[1 3])
              compositeGate(innerCircuit,[2 4])];
outerCircuit = quantumCircuit(outerGates)

outerCircuit = 

  quantumCircuit with properties:

    NumQubits: 4
        Gates: [2×1 quantum.gate.CompositeGate]
         Name: ""

Plot the outer circuit.

plot(outerCircuit)

In a circuit diagram, each solid horizontal line represents a qubit. The top line is a qubit with index 1 and the remaining lines from top to bottom are labeled sequentially. In this example, the plotted outer circuit consists of four qubits with indices 1, 2, 3, and 4. The plot shows that qubits 1 and 3 of the outer circuit are mapped to qubits 1 and 2 of the inner circuit of the first composite gate, and qubits 2 and 4 of the outer circuit are mapped to qubits 1 and 2 of the inner circuit of the second composite gate.

Click one of the composite gate blocks in the plot. A new figure showing the internal gates of the composite gate appears.

Construct Composite Gates from Inner Gates

Create an array of inner gates that consists of a Pauli X gate, a Hadamard gate, and a swap gate.

gates = [xGate(1); hGate(2); swapGate(1,2)]

gates = 

  3×1 SimpleGate array with gates:

    Id   Gate   Control   Target
     1   x                1     
     2   h                2     
     3   swap             [1,2] 

Create two composite gates from the array of inner gates. The first composite gate acts on qubits 1 and 4 of the outer circuit containing this gate. The second composite gate acts on qubits 2 and 3 of the outer circuit containing this gate.

cg1 = compositeGate(gates,[1 4],Name="custom");
cg2 = compositeGate(gates,[2 3],Name="custom");

Create a quantum circuit that consists of these two composite gates.

circuit = quantumCircuit([cg1; cg2])

circuit = 

  quantumCircuit with properties:

    NumQubits: 4
        Gates: [2×1 quantum.gate.CompositeGate]
         Name: ""

Plot the circuit.

plot(circuit)

The plotted circuit consists of four qubits with indices 1, 2, 3, and 4. The plot shows that qubits 1 and 4 of the circuit are mapped to qubits 1 and 2 of the inner gates of the first composite gate, and qubits 2 and 3 of the circuit are mapped to qubits 1 and 2 of the inner gates of the second composite gate.

Input Arguments

circuit — Inner circuit

quantumCircuit object

Inner circuit to construct the composite gate, specified as a quantumCircuit object.

gates — Inner gates

vector of gates

Inner gates to construct the composite gate, specified as a vector containing all the inner gates. The elements of this vector are of type SimpleGate or CompositeGate.

targetQubits — Target qubits of outer circuit

positive integer vector

Target qubits of the outer circuit, specified as a positive integer vector of qubit indices. The targetQubits vector maps each qubit of the inner circuit to a qubit of the outer circuit containing the composite gate. This vector must contain unique qubit indices.

name — Name of composite gate

string scalar | character vector

Name of the composite gate, specified as a string scalar or character vector. The name input must start with a letter, followed by letters, digits, or underscores (with no white space). This name is used in the plot of the composite gate and the function name in the generated QASM code.

If you construct a composite gate from an existing quantumCircuit object and you do not specify this name input, then the Name property of the circuit is copied to the Name property of the composite gate.

Version History

Introduced in R2023a