Changelog

Added

• Added DAG visualizer which requires Graphivz <https://www.graphviz.org/>_
  (#1059)
• Added an ASCII art circuit visualizer (#909)
• The QuantumCircuit class now returns an ASCII art visualization when treated
  as a string (#911)
• The QuantumCircuit class now has a draw() method which behaves the same
  as the qiskit.tools.visualization.circuit_drawer() function for visualizing
  the quantum circuit (#911)
• A new method hinton can be used on
  qiskit.tools.visualization.plot_state() to draw a hinton diagram (#1246)
• Two new constructor methods, from_qasm_str() and from_qasm_file(), to
  create a QuantumCircuit object from OpenQASM were added to the
  QuantumCircuit class. (#1172)
• New methods in QuantumCircuit for common circuit metrics:
  size(), depth(), width(), count_ops(), num_tensor_factors() (#1285)
• Added backend_monitor and backend_overview Jupyter magics,
  as well as plot_coupling_map (#1231)
• Added a Layout object (#1313)
• New plot_bloch_multivector() to plot Bloch vectors from a tensored state
  vector or density matrix. (#1359)
• Per-shot measurement results are available in simulators and select devices.
  Request them by setting memory=True in compile()/execute(),
  and retrieve them from result.get_memory() (#1385).
• Added a qiskit.converters module for translation between commonly used
  representations of a circuit: dag_to_circuits, circuits_to_dag,
  qobj_to_circuits, circuits_to_qobj, ast_to_dag.
• PassManager can schedule passes at init time (#1510).
• Added a .qobj() method for IBMQ and local simulator Jobs (#1532).
• New Decompose pass for decomposing a gate according to a rule (#1487).
• New Unroller pass in the transpiler for unrolling up to some basis (#1455).
• New BarrierBeforeFinalMeasurements pass for preventing final
  measure reorder (#1538).
• New CommutationAnalysis and CommutationTransformation transpiler
  passes for modifying a DAG based on gate commutativity relations (#1500).
• New transpiler mapper pass: BasicSwap (#1270).
• New transpiler mapper pass: LookaheadSwap (#1140).
• New transpiler mapper pass: StochasticSwap (#1520).
• New CXDirection pass for fixing the direction of cx gates (#1410).
• New CheckMap pass for checking if circuit meets mapping requirements (#1433).
• New Optimize1QGate pass for combining chains of 1q rotations (#1442).

Changed

• Evolved pass-based transpiler to support advanced functionality (#1060)
• .retrieve_job() and .jobs() no longer returns results by default,
  instead the result must be accessed by the result() method on the job
  objects (#1082).
• Make backend.status() dictionary conform with schema.
• The different output backends for the circuit_drawer() visualizations
  have been moved into separate private modules in
  qiskit.tools.visualizations. (#1105, #1111)
• DAG nodes contain pointers to Register and Instruction objects, rather
  than their string names (#1189).
• Upgraded some external dependencies to:
  • networkx>=2.2 (#1267).
• The qiskit.tools.visualization.circuit_drawer() method now returns
  a matplotlib.Figure object when the mpl output is used and a
  TextDrawer object when text output is used. (#1224, #1181)
• Speed up the Pauli class and extended its operators (#1271 #1166).
• IBMQ.save_account() now takes an overwrite option to replace an existing
  account on disk. Default is False (#1295).
• Backend and Provider methods defined in the specification use model objects
  rather than dicts, along with validation against schemas (#1249, #1277,
  #1350). The updated methods include:
  • backend.status() (#1301).
  • backend.configuration() (and __init__) (#1323).
  • backend.properties(), returning None for sims (#1331, #1401).
  • qiskit.Result (#1360).
• backend.provider() is now a method instead of a property (#1312).
• Remove local backend (Aer) fallback (#1303)
• The signatures for the plotting functions in
  qiskit.tools.visualization._counts_visualization.py,
  qiskit.tools.visualization._state_visualization.py, and
  qiskit.tools.visualization.interactive have been modified to make them
  in-line with standard Matplotlib calling conventions (#1359).
• Remove local backend (Aer) fallback (#1303).
• DAGCircuits store Instruction and Register objects, instead of name
  references. The DAGCircuit class methods are updated accordingly (#1210).
• transpile() now takes QuantumCircuit(s) to QuantumCircuit(s), and DAG
  processing is only done internally (#1397).
• The different unrollers are deprecated. The only unrolling happens
  from DAG to DAG (#1210).
• Moved all the circuit modules into a circuit module but for most users it
  is still imported in the top level for QuantumCircuit, QuantumRegister,
  ClassicalRegister
• qiskit.backends has been renamed to qiskit.providers (#1531).
• qiskit.backends.aer has been removed in favor of
  qiskit.providers.builtinsimulators (Python simulators) and
  qiskit.providers.legacysimulators (C++ simulators) (#1484)
• Aer in qiskit root module depends on having the
  qiskit-aer package installed, by default it is not present. Instead there are
  2 new provider instances in the root module BasicAer which provides the
  Python simulators and LegacySimulators which provides the old C++
  simulators in qiskit-terra. (#1484)

Deprecated

• plot_circuit(), latex_circuit_drawer(), generate_latex_source(),
  and matplotlib_circuit_drawer() from qiskit.tools.visualization are
  deprecated. Instead the circuit_drawer() function from the same module
  should be used. (#1055)
• The current default output of circuit_drawer() (using latex and falling
  back on python) is deprecated and will be changed in the future. (#1055)
• The qiskit.wrapper.load_qasm_string() and qiskit.wrapper.load_qasm_file()
  functions are deprecated and the QuantumCircuit.from_qasm_str() and
  QuantumCircuit.from_qasm_file() contstructor methods should be used instead
  (#1172)
• The plot_barriers and reverse_bits keys in the style kwarg dict
  are deprecated, instead the qiskit.tools.visualization.circuit_drawer()
  kwargs plot_barriers and reverse_bits should be used instead. (#1180)
• The transpile_dag() function format kwarg for emitting different
  output formats is deprecated (#1319).
• Several methods of qiskit.Result have been deprecated (#1360).
• The functions plot_state() and iplot_state() have been depreciated.
  Instead the functions plot_state_*() and iplot_state_*() should be
  called. (#1359)
• The skip_transpiler arg has been deprecated from compile() and
  execute() in favor of using the PassManager directly.

Fixed

• Fixed a variety of typos throughout sources (#1139)
• Fixed horizontal spacing when drawing barriers before CCNOT gates in latex
  circuit plots (#1051)
• Use case insensitive matching when comparing premium account URLs. (#1102)
• Fixed AerJob status when the submitted Job is in a PENDING state. (#1215)
• Add fallback for when CPU count can't be determined (#1214)
• Fix random_state from returning nan (#1258)
• The Clifford simulator run() method now works correctly with the updated
  AerJob usage (#1125)
• Fixed an edge case when connection checks would raise an unhandled exception
  (#1226)
• Fixed a bug where the transpiler moved middle-of-circuit measurements to the
  end (#1334)
• The number_to_keep kwarg in plot_histgram() now functions correctly
  (#1359).
• parallel_map no longer creates a progress bar for a single circuit (#1394).
• The timeout parameter is now passed into the inner _wait_for_submission
  function in IBMQJob from _wait_for_result (#1542).

Removed

• Remove register, available_backends (#1131).
• Remove tools/apps (#1184).
• Removed the dependency on IBMQuantumExperience, as it is now included
  in qiskit.backends.IBMQ (#1198).
• matplotlib is no longer in the package requirements and is now an
  optional dependency. In order to use any matplotlib based visualizations
  (which includes the qiskit.tools.visualization.circuit_drawer()
mpl output,
  qiskit.tools.visualization.plot_state,
  qiskit.tools.visualization.plot_histogram, and
  qiskit.tools.visualization.plot_bloch_vector you will now need to ensure
  you manually install and configure matplotlib independently.
• The basis kwarg for the circuit_drawer() function to provide an
  alternative list of basis gates has been removed. Instead users should adjust
  the basis gates prior to visualizing the circuit. (#1151)
• backend.parameters() and backend.calibration() have been fully
  deprecated, in favour of backend.properties() (#1305).
• The qiskit.tools.file_io module has been removed. Conversion between
  qiskit.Result and json can be achieved using .to_dict() and
  .from_dict() directly (#1360).
• The qiskit.Result class method for len() and indexing have been
  removed, along with the functions that perform post-processing (#1351).
• The get_snapshot() and get_snapshots() method from the Result
  class has been removed. Instead you can access the snapshots in a Result
  using Result.data()['snapshots'].
• Completed the deprecation of job.backend_name(), job.id(), and the
  backend_name parameter in its constructor.
• The qiskit.Result class now does post-processing of results returned
  from backends if they are called via the Result.get_xxx() methods
  (i.e. get_counts(), get_memory(), get_statevector(),
  get_unitary()). The raw data is accessible through Result.data()
  (#1404).
• The transpile() function kwarg format has been removed and will
  always return a circuit object. Instead you'll need to manually convert the
  output with the functions provided in qiskit.converters.