v0.2.12

[0.2.12] - 2026-04-28

Added

• Path Integral simulation backend — new exact-amplitude simulator (kPathIntegral) integrated into the QCSim common interface, supporting amplitudes, measurements, sampling, and Pauli-string expectation values. Exposed through the factory and the SimulatorConfig(simulator_type="path_integral") Python API
• Path Integral Python bindings — amplitude_from_zero() and amplitude() methods on QuantumCircuit for computing exact transition amplitudes via path integrals
• IsBranching() method on all quantum gate types, used by the path integral simulator to identify branching operations
• Path Integral via Network interface — SimpleDisconnectedNetwork now dispatches path integral jobs; multithreading is disabled for path integral simulators in networks when measurements are only at the end
• Coherent noise model — NoiseModel now supports deterministic rotation-gate noise injection (Rx/Ry/Rz) alongside stochastic Pauli channels. Coherent angle is derived from error probability via ε = 2·arcsin(√p) to match per-gate infidelity
• Coherent noise setters: set_coherent_depolarizing(), set_coherent_dephasing(), set_coherent_bit_flip(), set_coherent_rotation(), set_all_coherent_depolarizing()
• T1 amplitude damping noise — set_t1(), set_all_t1(), set_t1_from_time() for per-qubit T1 decay with physical time-constant conversion (γ = 1 − e^(−t_gate/T₁))
• ZZ crosstalk noise — set_crosstalk() for pairwise qubit coupling injection
• coherent_execute / coherent_estimate — Python bindings for executing circuits and estimating expectation values with coherent rotation noise
• full_noise_execute / full_noise_estimate — combined noise pipeline applying coherent + crosstalk + T1 + Pauli noise in a single call
• Comprehensive test suites: 600+ lines of path integral C++ tests (random circuits, amplitudes, measurements, sampling, Pauli strings), 290+ lines of network simulator tests, 1200+ lines of new Python binding tests covering all noise modes
• Noise simulation and path integral sections in TUTORIAL.md with usage examples

Changed

• NoiseModel header expanded to support Pauli, coherent, T1, and crosstalk noise in a unified model — both modes can be configured on the same instance
• QCSimSimulator routes all gate types through the path integral backend when kPathIntegral simulation type is selected
• QCSimState extended with path integral simulator state management, amplitude computation, and measurement support
• Doxygen upgraded to latest version; docs CI workflow updated
• Python package version bumped to 0.2.12

Fixed

• Missing public: access specifier on PathIntegralSimulator class methods
• Include path issues for Linux compilation in network simulator tests
• Compile warnings in NetworkJob.h and SimpleDisconnectedNetwork.h