Changelog

Improvements

• Introduce providers and rework backends (#376).
  • Split backends into local and ibmq.
  • Each provider derives from the following classes for its specific requirements.
    BaseProvider class.
    BaseBackend class.
    BaseJob class.
  • Allow querying result by both circuit name and QuantumCircuit instance.
• Introduce the QISKit wrapper (#376).
  • Introduce convenience wrapper functions around commonly used QISKit components
    (e.g. compile and execute functions).
  • Introduce the DefaultQISKitProvider, which acts as a context manager for the current session
    (e.g. providing easy access to all available_backends).
  • Avoid relying on QuantumProgram (eventual deprecation).
  • The functions are also available as top-level functions (for example,
    qiskit.get_backend()).
• Introduce BaseJob class and asynchronous jobs (#403).
  • Return BaseJob after run().
  • Mechanisms for querying status and results, or to cancel a job
• Introduce a skip_transpiler flag for compile() (#411).
• Introduce schemas for validating interfaces between qiskit and backends (#434)
  • qobj_schema
  • result_schema
  • job_status_schema
  • default_pulse_config_schema
  • backend_config_schema
  • backend_props_schema
  • backend_status_schema
• Improve C++ simulator (#386)
  • Add tensor_index.hpp for multi-partite qubit vector indexing.
  • Add qubit_vector.hpp for multi-partite qubit vector algebra.
  • Rework C++ simulator backends to use QubitVector class instead of std::vector.
• Improve interface to simulator backends (#435)
  • Introduce local_statevector_simulator_py and local_statevector_simulator_cpp.
  • Introduce aliased and deprecated backend names and mechanisms for resolving them.
  • Introduce optional compact flag to query backend names only by unique function.
  • Introduce result convenience functions get_statevector, get_unitary
  • Add snapshot command for caching a copy of the current simulator state.
• Introduce circuit drawing via circuit_drawer() and plot_circuit() (#295, #414)
• Introduce benchmark suite for performance testing (test/performance) (#277)
• Introduce more robust probability testing via assertDictAlmostEqual (#390)
• Allow combining circuits across both depth and width (#389)
• Enforce string token names (#395)

Bug Fixes

• Fix coherent error bug in local_qasm_simulator_cpp (#318)
• Fix the order and format of result bits obtained from device backends (#430)
• Fix support for noises in the idle gate of local_clifford_simulator_cpp (#440)
• Fix JobProcessor modifying input qobj (#392) (and removed JobProcessor during #403)
• Fix ability to apply all gates on register (#369)

Backward-incompatible changes

• Some methods of QuantumProgram are soon to be deprecated. Please use the
  top-level functions instead.
• The Register instantiation now expects size, name. Using
  name, size is still supported but will be deprecated in the future.
• Simulators no longer return wavefunction by setting shots=1. Instead,
  use the local_statevector_simulator, or explicitly ask for snapshot.
• Return job instance after run(), rather than result.
• Rename simulators according to PROVIDERNAME_SIMPLEALIAS_simulator_LANGUAGEORPROJECT
• Move simulator extensions to qiskit/extensions/simulator
• Move Rzz and CSwap to standard extension library