Results of sampling circuit with custom unitary don't match between qiskit 1.4 and qiskit 2 #2347
Description
Informations
- Qiskit Aer version: 0.17.1
- Python version: 3.11
- Operating system: Linux
What is the current behavior?
When sampling - using Aer 0.17.1 - from a circuit with some custom unitaries, I'm seeing markedly different counts being returned.
- With Qiskit 1.4.3
Counts: {'011011': 38, '101100': 149, '001111': 123, '101010': 55, '111111': 48, '000011': 401, '000111': 135, '100100': 149, '100101': 37, '001101': 131, '110101': 47, '000010': 378, '110111': 46, '010100': 161, '010111': 47, '001100': 417, '001000': 388, '111101': 57, '101101': 42, '010000': 413, '100000': 417, '100110': 34, '101110': 48, '111001': 51, '001010': 166, '111100': 123, '110000': 411, '110001': 151, '011101': 46, '011010': 43, '000001': 470, '100001': 136, '010101': 41, '000000': 1230, '011110': 35, '100111': 48, '000100': 439, '111011': 57, '011000': 131, '001011': 160, '011100': 144, '110010': 151, '011001': 48, '101000': 127, '110110': 39, '100011': 131, '110100': 134, '111110': 65, '000110': 140, '010001': 136, '100010': 122, '111000': 145, '010011': 147, '011111': 59, '010010': 132, '001001': 140, '001110': 149, '101011': 49, '101111': 44, '101001': 42, '111010': 41, '010110': 34, '000101': 148, '110011': 134}
- With Qiskit 2.0.2
Counts: {'000011': 1700, '000010': 1630, '000000': 5015, '000001': 1655}
Tagging @fpietra and @matteacrossi who've been investigating this issue on our side. I've also opened Qiskit/qiskit#14569, as I don't know whether the problem lies with Qiskit, Aer, or the interaction of the two
Steps to reproduce the problem
The reproducer circuit and script are in this repo Building the two Dockerfiles will provide two images with the dependencies to run the comparison for the two different qiskit versions.
What is the expected behavior?
I'd expect the behavior from qiskit 1.4.3 to be preserved with the new major release series. I'm not sure whether this is a problem with Qiskit Aer though.