Main user-facing entry points for building and using Q2NS. More...

Classes
class	q2ns::NetController
	Main user-facing facade for creating and configuring a quantum network. More...

class	q2ns::QNode
	Main user-facing per-node API for quantum operations and transmission. More...

class	q2ns::Qubit
	Lightweight handle for one qubit inside a registry-managed state. More...

Functions
double	q2ns::analysis::Fidelity (const QState &a, const QState &b)
	Compute fidelity between two QState objects of the same backend type.

double	q2ns::analysis::Purity (const QState &s)
	Compute the purity of a quantum state.

bool	q2ns::analysis::IsPure (const QState &s, double tol=1e-12)
	Check whether a quantum state is pure within a numerical tolerance.

double	q2ns::analysis::VonNeumannEntropy (const QState &s)
	Compute the von Neumann entropy of a quantum state in bits.

double	q2ns::analysis::TraceDistance (const QState &a, const QState &b)
	Compute the trace distance between two QState objects of the same backend type.

Detailed Description

Main user-facing entry points for building and using Q2NS.

Function Documentation

◆ Fidelity()

double q2ns::analysis::Fidelity	(	const QState &	a,
		const QState &	b
	)

Compute fidelity between two QState objects of the same backend type.

Currently supported backend pairings are:

Mixed backend comparisons are not yet supported and throw.

Parameters

a	First state.
b	Second state.

Returns: Fidelity in the range [0.0, 1.0].

Exceptions

std::invalid_argument	if the states are empty.
std::runtime_error	if the states have different sizes, use unsupported backends, or require unavailable backend-specific functionality.

See also: QState

Definition at line 207 of file q2ns-analysis.cc.

References q2ns::QState::NumQubits().

Referenced by main(), q2ns::SwapApp::TryApply(), anonymous_namespace{q2ns-5-noisy-teleportation-example.cc}::TryCorrections(), and anonymous_namespace{q2ns-5-noisy-teleportation-advanced-example.cc}::TryCorrections().

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◆ IsPure()

bool q2ns::analysis::IsPure	(	const QState &	s,
		double	tol = `1e-12`
	)

Check whether a quantum state is pure within a numerical tolerance.

This function evaluates purity and compares it against 1.0. It is intended as a convenience helper for diagnostics, tests, and analysis code.

Parameters

s	Input state.
tol	Absolute tolerance for comparing purity against 1.0.

Returns: True if the state is pure within tolerance, false otherwise.

Exceptions

std::invalid_argument	if the state is empty or if tol is negative.
std::runtime_error	if the backend is unsupported or requires unavailable backend-specific functionality.

See also: Purity; QState

Definition at line 280 of file q2ns-analysis.cc.

References q2ns::analysis::Purity().

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◆ Purity()

double q2ns::analysis::Purity ( const QState & s )

Compute the purity of a quantum state.

Purity is defined as Tr(rho^2), where rho is the density matrix of the state. It is equal to 1 for pure states and less than 1 for mixed states.

For backend-specific reasons, this function currently operates only on a single QState and therefore does not involve cross-backend comparison.

Parameters

s	Input state.

Returns: Purity in the range [0.0, 1.0], up to numerical tolerance.

Exceptions

std::invalid_argument	if the state is empty.
std::runtime_error	if the backend is unsupported or requires unavailable backend-specific functionality.

See also: IsPure; VonNeumannEntropy; QState

Definition at line 264 of file q2ns-analysis.cc.

References q2ns::QState::NumQubits().

Referenced by q2ns::analysis::IsPure().

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◆ TraceDistance()

double q2ns::analysis::TraceDistance	(	const QState &	a,
		const QState &	b
	)

Compute the trace distance between two QState objects of the same backend type.

The trace distance is defined as D(rho, sigma) = 0.5 * ||rho - sigma||_1, where ||.||_1 is the trace norm.

Currently supported backend pairings are:

Mixed backend comparisons are not supported and throw.

Parameters

a	First state.
b	Second state.

Returns: Trace distance in the range [0.0, 1.0], up to numerical tolerance.

Exceptions

std::invalid_argument	if the states are empty.
std::runtime_error	if the states have different sizes, use unsupported backends, or require unavailable backend-specific functionality.

See also: Fidelity; VonNeumannEntropy; QState

Definition at line 337 of file q2ns-analysis.cc.

References q2ns::QState::NumQubits().

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◆ VonNeumannEntropy()

double q2ns::analysis::VonNeumannEntropy ( const QState & s )

Compute the von Neumann entropy of a quantum state in bits.

The von Neumann entropy is defined as S(rho) = -Tr(rho log2 rho).

Eigenvalues whose magnitude is below numerical tolerance are treated as zero and do not contribute to the sum.

Parameters

s	Input state.

Returns: von Neumann entropy in bits.

Exceptions

std::invalid_argument	if the state is empty.
std::runtime_error	if the backend is unsupported, if the backend requires unavailable functionality, or if the density matrix is not positive semidefinite within numerical tolerance.

See also: Purity; TraceDistance; QState

Definition at line 290 of file q2ns-analysis.cc.

References q2ns::H, and q2ns::QState::NumQubits().

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Classes

Functions

Detailed Description

Function Documentation

◆ Fidelity()

◆ IsPure()

◆ Purity()

◆ TraceDistance()

◆ VonNeumannEntropy()