---
upgrade:
  - |
    Add ``gate_length_units`` kwarg to
    :meth:`qiskit.providers.aer.noise.NoiseModel.from_device`
    for specifying custom ``gate_lengths`` in the device noise model function
    to handle unit conversions for internal code.
fixes:
  - |
    Fix error in gate time unit conversion for device noise model with thermal
    relaxation errors and gate errors. The error probability the depolarizing
    error was being  calculated with gate time in microseconds, while for
    thermal relaxation it was being calculated in nanoseconds. This resulted
    in no depolarizing error being applied as the incorrect units would make
    the device seem to be coherence limited.
  - |
    Fix bug in incorrect composition of QuantumErrors when the qubits of
    composed instructions differ.
