squander::density::PhaseDampingOp Class Reference

Phase damping channel (T2 dephasing): loss of coherence. More...

#include <noise_operation.h>

Inheritance diagram for squander::density::PhaseDampingOp:

Public Member Functions
void	apply_to_density (const double *params, int param_count, DensityMatrix &rho) override
	Apply this operation to the density matrix. More...
std::unique_ptr< IDensityOperation >	clone () const override
	Create a deep copy of this operation. More...
double	get_lambda () const
std::string	get_name () const override
	Get operation name for debugging/display. More...
int	get_parameter_num () const override
	Get number of free parameters this operation requires. More...
int	get_target_qbit () const
bool	is_parametric () const
bool	is_unitary () const override
	Check if this is a unitary operation (gate) or non-unitary (noise) More...
	PhaseDampingOp (int target_qbit, double lambda)
	Create phase damping with fixed lambda. More...
	PhaseDampingOp (int target_qbit)
	Create parametric phase damping (1 parameter) More...

Private Member Functions
void	apply_phase_damping (DensityMatrix &rho, double lambda)

Private Attributes
double	fixed_lambda_
bool	is_parametric_
int	target_qbit_

Detailed Description

Phase damping channel (T2 dephasing): loss of coherence.

Models phase randomization without energy loss. Represents decoherence in real quantum systems where the environment measures the qubit in the computational basis.

Kraus operators:

• K₀ = [[1, 0], [0, √(1-λ)]]
• K₁ = [[0, 0], [0, √λ]]

where λ = 1 - exp(-t/T2) is the dephasing parameter.

Properties:

• λ = 0: No dephasing (identity channel)
• λ = 1: Complete dephasing (diagonal state)
• Only affects off-diagonal elements (coherences)
• Diagonal elements unchanged

Can be parametric (λ from parameter array) or fixed.

Definition at line 208 of file noise_operation.h.

Constructor & Destructor Documentation

PhaseDampingOp() [1/2]

squander::density::PhaseDampingOp::PhaseDampingOp	(	int	target_qbit,
		double	lambda
	)

Create phase damping with fixed lambda.

Parameters

target_qbit	Target qubit index
lambda	Dephasing parameter λ = 1 - exp(-t/T2) ∈ [0, 1]

Definition at line 320 of file noise_operation.cpp.

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PhaseDampingOp() [2/2]

squander::density::PhaseDampingOp::PhaseDampingOp ( int  target_qbit )

explicit

Create parametric phase damping (1 parameter)

Parameters

target_qbit

Target qubit index

Definition at line 330 of file noise_operation.cpp.

Member Function Documentation

apply_phase_damping()

void squander::density::PhaseDampingOp::apply_phase_damping ( DensityMatrix &  rho, double  lambda  )

private

Definition at line 358 of file noise_operation.cpp.

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apply_to_density()

void squander::density::PhaseDampingOp::apply_to_density ( const double *  params, int  param_count, DensityMatrix &  rho  )

overridevirtual

Apply this operation to the density matrix.

Parameters

params	Pointer to this operation's parameters (may be nullptr if param_count=0)
param_count	Number of parameters for this operation
rho	The density matrix to modify in-place

Implements squander::density::IDensityOperation.

Definition at line 337 of file noise_operation.cpp.

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clone()

std::unique_ptr< IDensityOperation > squander::density::PhaseDampingOp::clone ( ) const

overridevirtual

Create a deep copy of this operation.

Returns

Unique pointer to the cloned operation

Implements squander::density::IDensityOperation.

Definition at line 388 of file noise_operation.cpp.

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get_lambda()

double squander::density::PhaseDampingOp::get_lambda ( ) const

inline

Definition at line 233 of file noise_operation.h.

get_name()

std::string squander::density::PhaseDampingOp::get_name ( ) const

inlineoverridevirtual

Get operation name for debugging/display.

Returns

Human-readable name (e.g., "H", "CNOT", "Depolarizing")

Implements squander::density::IDensityOperation.

Definition at line 227 of file noise_operation.h.

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get_parameter_num()

int squander::density::PhaseDampingOp::get_parameter_num ( ) const

inlineoverridevirtual

Get number of free parameters this operation requires.

Returns

Number of parameters (0 for constant gates/fixed noise)

Implements squander::density::IDensityOperation.

Definition at line 226 of file noise_operation.h.

get_target_qbit()

int squander::density::PhaseDampingOp::get_target_qbit ( ) const

inline

Definition at line 232 of file noise_operation.h.

is_parametric()

bool squander::density::PhaseDampingOp::is_parametric ( ) const

inline

Definition at line 234 of file noise_operation.h.

is_unitary()

bool squander::density::NoiseOperation::is_unitary ( ) const

inlineoverridevirtualinherited

Check if this is a unitary operation (gate) or non-unitary (noise)

Returns

true for unitary gates, false for noise channels

Implements squander::density::IDensityOperation.

Definition at line 38 of file noise_operation.h.

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Member Data Documentation

fixed_lambda_

double squander::density::PhaseDampingOp::fixed_lambda_

private

Definition at line 238 of file noise_operation.h.

is_parametric_

bool squander::density::PhaseDampingOp::is_parametric_

private

Definition at line 239 of file noise_operation.h.

target_qbit_

int squander::density::PhaseDampingOp::target_qbit_

private

Definition at line 237 of file noise_operation.h.

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The documentation for this class was generated from the following files:

• noise_operation.h
• noise_operation.cpp