Gates

A gate is a unitary operation applied to one or more qubits. FQkit provides a Gate base class plus ready-made factories for the common gates.

Single-qubit gates

Gate	Call	Parameterized	Description
Hadamard	`Hadamard()`	no	Creates superposition
RX	`RX(theta)`	yes	Rotation about the X axis
RY	`RY(theta)`	yes	Rotation about the Y axis
RZ	`RZ(theta)`	yes	Rotation about the Z axis

Multi-qubit gates

Gate	Call	Qubits	Description
CNOT	`CNOT()`	2	Controlled-NOT (control, target)
CZ	`CZ()`	2	Controlled-Z
SWAP	`SWAP()`	2	Swaps two qubits
Toffoli	`Toffoli()`	3	Controlled-controlled-NOT

What each gate looks like

Qubit 0 is the top wire. These are the same symbols used in the tutorials and in the notebooks.

Hadamard

RX, a rotation about X

RY, a rotation about Y

RZ, a rotation about Z

CNOT. The dot is the control, the plus is the target.

CZ. Both qubits get a dot.

SWAP

Toffoli. Two controls, then a target.

Using a gate

Gates are added to a circuit with add_gate(gate, targets). The first target qubit is the gate’s most significant qubit. For CNOT, that is the control.


from fqkit import QuantumCircuit, Hadamard, CNOT, SWAP
 
qc = QuantumCircuit(3)
qc.add_gate(Hadamard(), [0])
qc.add_gate(CNOT(), [0, 1])      # control=0, target=1
qc.add_gate(SWAP(), [1, 2])

Parameterized gates

Rotation gates take an angle in radians. Pass a number directly, or a symbolic Parameter to bind later:


from fqkit import RX, Parameter
 
qc.add_gate(RX(1.5708), [0])          # numeric angle
 
theta = Parameter("theta")
qc.add_gate(RX(theta), [0])           # symbolic: bind before running

Custom gates

You can build any gate from its unitary matrix:


from fqkit import Gate
 
# A single-qubit identity gate
my_gate = Gate("I", 1, matrix=[[1, 0], [0, 1]])