Density-matrix concrete QState backend using qpp::cmat. More...

#include <q2ns-qstate-dm.h>

Inheritance diagram for q2ns::QStateDM:

Collaboration diagram for q2ns::QStateDM:

Public Member Functions
	QStateDM (std::size_t numQubits)
	Construct the \|0...0><0...0\| state on numQubits qubits.

	QStateDM (qpp::cmat rho)
	Construct from an existing density matrix.

int64_t	AssignStreams (int64_t stream) override
	Assign RNG streams for deterministic randomness.

void	Print (std::ostream &os) const override
	Print a human-readable representation of the state.

std::size_t	NumQubits () const override
	Return the number of logical qubits in the state.

void	Apply (const QGate &g, const std::vector< q2ns::Index > &targets) override
	Apply a gate to the given target qubits.

std::shared_ptr< QState >	MergeDisjoint (const QState &other) const override
	Return the disjoint merge of this state and another density-matrix backend.

MeasureResult	Measure (q2ns::Index target, q2ns::Basis basis=q2ns::Basis::Z) override
	Measure one qubit in the requested basis and split the result.

const qpp::cmat &	GetRho () const
	Return the underlying density matrix.

void	SetRho (const qpp::cmat &rho)
	Replace the underlying density matrix after validation.

std::shared_ptr< QState >	PartialTrace (const std::vector< q2ns::Index > &subsystemA)
	Extract a subsystem by partial trace.

Public Member Functions inherited from q2ns::QState
virtual	~QState ()
	Virtual destructor.

StateId	GetStateId () const
	Get the registry-assigned state id.

void	SetStateId (StateId id)
	Set the registry-assigned state id.

virtual void	Apply (const QGate &g, const std::vector< Index > &targets)=0
	Apply a gate to the given target indices.

Static Private Member Functions
static void	ValidateDensityMatrix (const qpp::cmat &rho)
	Validate basic density-matrix structure.

Private Attributes
qpp::cmat	rho_
	Backend density matrix.

Additional Inherited Members
Protected Member Functions inherited from q2ns::QState
void	PrintHeader (std::ostream &os, const char *backendName) const
	Print a standard backend header.

Static Protected Member Functions inherited from q2ns::QState
static uint64_t	SplitMix64 (uint64_t x)
	Mix a 64-bit value deterministically.

static uint64_t	DeriveSeed64 (uint32_t seed, uint32_t run, int64_t stream, uint64_t salt)
	Derive a deterministic 64-bit seed from ns-3 seed/run and a stream.

static std::seed_seq	MakeSeedSeq (uint64_t s64)
	Build a std::seed_seq from a 64-bit seed.

static void	CheckSeedRunNonZero (uint32_t seed, uint32_t run)
	Abort if ns-3 seed or run is zero.

template<uint64_t SALT>
static bool	ShouldReseed (uint32_t seed, uint32_t run, int64_t stream)
	Return whether a backend-global RNG should be reseeded.

template<uint64_t SALT, typename ReseedFn >
static int64_t	AssignStreamsGlobal (int64_t stream, ReseedFn reseed_fn)
	Helper for backends that reseed a global RNG source.

Detailed Description

Density-matrix concrete QState backend using qpp::cmat.

QStateDM stores an N-qubit state as a 2^N by 2^N density matrix and implements the common QState interface.

Supported behavior includes:

general unitary evolution
single-qubit measurement via basis rotation and projective measurement
disjoint merge by tensor product
partial trace extraction of subsystems

Constructors validate basic density-matrix structure such as square shape, power-of-two dimension, and trace close to one.

See also: QState; QStateKet

Definition at line 45 of file q2ns-qstate-dm.h.

Constructor & Destructor Documentation

◆ QStateDM() [1/2]

q2ns::QStateDM::QStateDM ( std::size_t numQubits )

explicit

Construct the |0...0><0...0| state on numQubits qubits.

Parameters

numQubits Number of qubits.

Definition at line 80 of file q2ns-qstate-dm.cc.

References rho_, and ValidateDensityMatrix().

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◆ QStateDM() [2/2]

q2ns::QStateDM::QStateDM ( qpp::cmat rho )

explicit

Construct from an existing density matrix.

Parameters

rho	Density matrix.

Exceptions

std::invalid_argument if the matrix is not square, not Hermitian, not positive semidefinite, not of dimension 2^N, or does not have trace one.

Definition at line 89 of file q2ns-qstate-dm.cc.

References rho_, and ValidateDensityMatrix().

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Member Function Documentation

◆ Apply()

void q2ns::QStateDM::Apply	(	const QGate &	g,
		const std::vector< q2ns::Index > &	targets
	)

override

Apply a gate to the given target qubits.

Parameters

g	Gate descriptor.
targets	Target qubit indices.

Definition at line 120 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), q2ns::Custom, q2ns::MatrixOf(), and rho_.

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◆ AssignStreams()

int64_t q2ns::QStateDM::AssignStreams ( int64_t stream )

overridevirtual

Assign RNG streams for deterministic randomness.

This seeds qpp's random source for measurement and other stochastic qpp operations used by this backend.

Parameters

stream Starting stream index.

Returns: Number of streams consumed.

Reimplemented from q2ns::QState.

Definition at line 95 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), and q2ns::QState::MakeSeedSeq().

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◆ GetRho()

const qpp::cmat & q2ns::QStateDM::GetRho ( ) const

inline

Return the underlying density matrix.

Returns: Reference to the backend density matrix.

See also: SetRho

Definition at line 120 of file q2ns-qstate-dm.h.

References rho_.

◆ Measure()

QState::MeasureResult q2ns::QStateDM::Measure	(	q2ns::Index	target,
		q2ns::Basis	basis = `q2ns::Basis::Z`
	)

overridevirtual

Measure one qubit in the requested basis and split the result.

The returned measured state is a 1-qubit density matrix expressed in the requested measurement basis. The survivors state contains the remaining qubits in their original relative order.

Parameters

target	Index of the qubit to measure.
basis	Measurement basis. Defaults to Z.

Returns: Measurement result containing outcome, measured state, and survivor state.

Implements q2ns::QState.

Definition at line 156 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), q2ns::H, NumQubits(), rho_, q2ns::S, q2ns::X, q2ns::Y, and q2ns::Z.

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◆ MergeDisjoint()

std::shared_ptr< QState > q2ns::QStateDM::MergeDisjoint ( const QState & other ) const

overridevirtual

Return the disjoint merge of this state and another density-matrix backend.

The merged qubit order is [this-qubits..., other-qubits...].

Parameters

other Other state to merge with.

Returns: Newly allocated merged state.

Implements q2ns::QState.

Definition at line 144 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), and rho_.

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◆ NumQubits()

std::size_t q2ns::QStateDM::NumQubits ( ) const

overridevirtual

Return the number of logical qubits in the state.

Returns: Number of logical qubits.

Implements q2ns::QState.

Definition at line 106 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), and rho_.

Referenced by Measure(), and PartialTrace().

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◆ PartialTrace()

std::shared_ptr< QState > q2ns::QStateDM::PartialTrace ( const std::vector< q2ns::Index > & subsystemA )

Extract a subsystem by partial trace.

The qubits listed in subsystemA are kept in the returned state. This object is mutated to become the complementary subsystem.

Parameters

subsystemA Indices of the subsystem to keep in the returned state.

Returns: New state representing subsystemA.

Definition at line 204 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), NumQubits(), rho_, and ValidateDensityMatrix().

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◆ Print()

void q2ns::QStateDM::Print ( std::ostream & os ) const

overridevirtual

Print a human-readable representation of the state.

Parameters

os	Output stream.

Implements q2ns::QState.

Definition at line 113 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), q2ns::QState::PrintHeader(), and rho_.

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◆ SetRho()

void q2ns::QStateDM::SetRho ( const qpp::cmat & rho )

Replace the underlying density matrix after validation.

Parameters

rho	New density matrix.

Exceptions

std::invalid_argument if the matrix is not square, not Hermitian, not positive semidefinite, not of dimension 2^N, or does not have trace one.

See also: GetRho

Definition at line 252 of file q2ns-qstate-dm.cc.

References q2ns::QState::AssignStreamsGlobal(), rho_, and ValidateDensityMatrix().

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◆ ValidateDensityMatrix()

void q2ns::QStateDM::ValidateDensityMatrix ( const qpp::cmat & rho )

staticprivate

Validate basic density-matrix structure.

Parameters

rho	Density matrix to validate.

Definition at line 25 of file q2ns-qstate-dm.cc.

References q2ns::H.

Referenced by PartialTrace(), QStateDM(), QStateDM(), and SetRho().

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Member Data Documentation

◆ rho_

qpp::cmat q2ns::QStateDM::rho_

private

Backend density matrix.

Definition at line 152 of file q2ns-qstate-dm.h.

Referenced by Apply(), GetRho(), Measure(), MergeDisjoint(), NumQubits(), PartialTrace(), Print(), QStateDM(), QStateDM(), and SetRho().

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

Public Member Functions

Static Private Member Functions

Private Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ QStateDM() [1/2]

◆ QStateDM() [2/2]

Member Function Documentation

◆ Apply()

◆ AssignStreams()

◆ GetRho()

◆ Measure()

◆ MergeDisjoint()

◆ NumQubits()

◆ PartialTrace()

◆ Print()

◆ SetRho()

◆ ValidateDensityMatrix()

Member Data Documentation

◆ rho_