Variational Gate — VQGate

Deprecated: The VariationalGate class has been removed from pyqpanda3. Variational gates are now created through VQCircuit and VQGate. See VQCircuit for the current API.

API reference for parameterized (variational) gate variants used in variational quantum circuits (VQAs). These gates differ from standard gates in that their rotation parameters are symbolic references (ParamExpression) into a Parameter array rather than fixed numeric values.

VQGate

Base class for variational quantum gates. VQGate objects are created by the variational gate factory functions (which are overloaded versions of standard gate functions taking a ParamExpression instead of a float) and can be appended to VQCircuit.

Signature

class VQGate

VQGate instances hold a gate type together with ParamExpression references into a Parameter array. At circuit execution time, concrete values are bound through VQCircuit.__call__().

ParamExpression and Parameter are defined in pyqpanda3.vqcircuit; ParamExpression instances are produced by VQCircuit.Param(...).

Variational Gate Factory Functions

Each function returns a VQGate. A param argument of type ParamExpression references a position in the Parameter array that supplies the rotation angle.

Single-Qubit Variational Gates

P (variational)

P(qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param	ParamExpression	Symbolic reference into the Parameter array

Returns a variational P gate.

RX (variational)

RX(qbit_idx: int, param: ParamExpression) -> VQGate

Returns a variational $R_X$ gate.

RY (variational)

RY(qbit_idx: int, param: ParamExpression) -> VQGate

Returns a variational $R_Y$ gate.

RZ (variational)

RZ(qbit_idx: int, param: ParamExpression) -> VQGate

Returns a variational $R_Z$ gate.

U1 (variational)

U1(qbit_idx: int, param: ParamExpression) -> VQGate

Returns a variational U1 gate.

IDLE (variational)

IDLE(qbit_idx: int, param: ParamExpression) -> VQGate

Returns a variational IDLE gate.

Two-Parameter Variational Gates

U2 (variational, overload 1)

U2(qbit_idx: int, param1: ParamExpression, param2: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	ParamExpression	Mutable parameter index for first angle
param2	Union[float, ParamExpression]	Fixed value or mutable parameter index for second angle

U2 (variational, overload 2)

U2(qbit_idx: int, param1: float, param2: ParamExpression) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	ParamExpression	Mutable parameter index for second angle

RPhi (variational, overload 1)

RPhi(qbit_idx: int, param1: ParamExpression, param2: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	ParamExpression	Mutable parameter index for theta
param2	Union[float, ParamExpression]	Fixed value or mutable parameter index for phi

RPhi (variational, overload 2)

RPhi(qbit_idx: int, param1: float, param2: ParamExpression) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for theta
param2	ParamExpression	Mutable parameter index for phi

Three-Parameter Variational Gates

U3 (variational, overload 1)

U3(qbit_idx: int, param1: ParamExpression, param2: Union[float, ParamExpression], param3: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	ParamExpression	Mutable parameter index for first angle
param2	Union[float, ParamExpression]	Fixed value or mutable parameter index for second angle
param3	Union[float, ParamExpression]	Fixed value or mutable parameter index for third angle

U3 (variational, overload 2)

U3(qbit_idx: int, param1: float, param2: ParamExpression, param3: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	ParamExpression	Mutable parameter index for second angle
param3	Union[float, ParamExpression]	Fixed value or mutable parameter index for third angle

U3 (variational, overload 3)

U3(qbit_idx: int, param1: float, param2: float, param3: ParamExpression) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	float	Fixed value for second angle
param3	ParamExpression	Mutable parameter index for third angle

Four-Parameter Variational Gates

U4 (variational, overload 1)

U4(qbit_idx: int, param1: ParamExpression, param2: Union[float, ParamExpression], param3: Union[float, ParamExpression], param4: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	ParamExpression	Mutable parameter index for first angle
param2	Union[float, ParamExpression]	Fixed value or mutable parameter index for second angle
param3	Union[float, ParamExpression]	Fixed value or mutable parameter index for third angle
param4	Union[float, ParamExpression]	Fixed value or mutable parameter index for fourth angle

U4 (variational, overload 2)

U4(qbit_idx: int, param1: float, param2: ParamExpression, param3: Union[float, ParamExpression], param4: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	ParamExpression	Mutable parameter index for second angle
param3	Union[float, ParamExpression]	Fixed value or mutable parameter index for third angle
param4	Union[float, ParamExpression]	Fixed value or mutable parameter index for fourth angle

U4 (variational, overload 3)

U4(qbit_idx: int, param1: float, param2: float, param3: ParamExpression, param4: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	float	Fixed value for second angle
param3	ParamExpression	Mutable parameter index for third angle
param4	Union[float, ParamExpression]	Fixed value or mutable parameter index for fourth angle

U4 (variational, overload 4)

U4(qbit_idx: int, param1: float, param2: float, param3: float, param4: ParamExpression) -> VQGate

Parameter	Type	Description
qbit_idx	int	Target qubit index
param1	float	Fixed value for first angle
param2	float	Fixed value for second angle
param3	float	Fixed value for third angle
param4	ParamExpression	Mutable parameter index for fourth angle

Two-Qubit Variational Gates

CU (variational, overload 1)

CU(control_qbit_idx: int, target_qbit_idx: int, param1: ParamExpression, param2: Union[float, ParamExpression], param3: Union[float, ParamExpression], param4: Union[float, ParamExpression]) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param1	ParamExpression	Mutable parameter index for first angle
param2	Union[float, ParamExpression]	Fixed value or mutable parameter index for second angle
param3	Union[float, ParamExpression]	Fixed value or mutable parameter index for third angle
param4	Union[float, ParamExpression]	Fixed value or mutable parameter index for fourth angle

CU (variational, overloads 2-4)

Additional overloads follow the same pattern as U4, with one additional fixed value per overload. Each overload takes control_qbit_idx and target_qbit_idx as the first two arguments.

CP (variational)

CP(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

CRX (variational)

CRX(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

CRY (variational)

CRY(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

CRZ (variational)

CRZ(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

CR (variational, alias for CP)

CR(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

RXX (variational)

RXX(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

RYY (variational)

RYY(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

RZZ (variational)

RZZ(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

RZX (variational)

RZX(control_qbit_idx: int, target_qbit_idx: int, param: ParamExpression) -> VQGate

Parameter	Type	Description
control_qbit_idx	int	Control qubit index
target_qbit_idx	int	Target qubit index
param	ParamExpression	Mutable parameter index

Usage with VQCircuit

Variational gates are the building blocks of VQCircuit. A ParamExpression produced by VQCircuit.Param(...) refers to a position in the Parameter array:

from pyqpanda3.vqcircuit import VQCircuit
from pyqpanda3.core import RX, CP

# Create a variational circuit
vqc = VQCircuit()

# Initialize the parameter array: 1D with 3 elements, dimension label "params"
vqc.set_Param([3], ["params"])

# Create parameter placeholders at specific indices with element labels
p0 = vqc.Param([0], "rx0")   # parameter for first RX
p1 = vqc.Param([1], "rx1")   # parameter for second RX
p2 = vqc.Param([2], "cp")    # parameter for controlled-phase

# Add variational gates using parameter indices
vqc << RX(0, p0)         # RX on qubit 0, angle from p0
vqc << RX(1, p1)         # RX on qubit 1, angle from p1
vqc << CP(0, 1, p2)      # Controlled-Phase using p2
vqc << RX(0, p2)         # RX on qubit 0, angle from p2

# Get parameter values and bind concrete values
import numpy as np
theta = np.array([0.5, 0.3, 0.1])
result = vqc(theta)  # pass concrete values
print(type(result).__name__)

Output:

VQCResult

See Also

• VQCircuit — Variational quantum circuit class
• Parameter — Parameter vector class
• Gates — Standard (non-variational) gate functions
• Gradient — Gradient computation with variational gates