add support for single circuit on exeuctor run method (unitaryfund#2099)

* add support for single circuit on exeuctor run method

* upate authors list

* downgrade qiskit_aer version due to incompatibilities

DiagonalGate cannot be imported with version 0.13

* add single circuit tests to run method of executor

* run black on addded tests

AUTHORS

@@ -54,4 +54,5 @@ Mohammad Zuhair Khan
 Brian Goldsmith
 Farzad Kianvash
 Yash Prabhat
-Vladimir Kozhukalov
+Vladimir Kozhukalov
+Emiliano Godinez

dev_requirements.txt

@@ -1,6 +1,6 @@
 # Third-party integration.
 qiskit~=0.44.3
-qiskit-aer~=0.13.0
+qiskit-aer~=0.12.2
 qiskit-ibm-provider~=0.7.2
 pyquil~=3.5.4
 pennylane-qiskit~=0.33.0

mitiq/executor/executor.py

@@ -211,19 +211,22 @@ def evaluate(
 
     def run(
         self,
-        circuits: Sequence[QPROGRAM],
+        circuits: Union[QPROGRAM, Sequence[QPROGRAM]],
         force_run_all: bool = True,
         **kwargs: Any,
     ) -> Sequence[QuantumResult]:
         """Runs all input circuits using the least number of possible calls to
         the executor.
 
         Args:
-            circuits: Sequence of circuits to execute using the executor.
+            circuits: Circuit or sequence thereof to execute with the executor.
             force_run_all: If True, force every circuit in the input sequence
                 to be executed (if some are identical). Else, detects identical
                 circuits and runs a minimal set.
         """
+        if not isinstance(circuits, Sequence):
+            circuits = [circuits]
+
         start_result_index = len(self._quantum_results)
 
         if force_run_all:

mitiq/executor/tests/test_executor.py

@@ -101,6 +101,15 @@ def test_executor_non_hermitian_observable():
         executor.evaluate(circuits, obs)
 
 
+def test_run_executor_single_circuit():
+    collector = Executor(executor=executor_serial)
+    circuit = cirq.Circuit(cirq.H(cirq.LineQubit(0)))
+    results_no_sequence = collector.run(circuit)
+    results_sequence = collector.run([circuit])
+    assert np.allclose(results_no_sequence, np.zeros(1))
+    assert np.allclose(results_no_sequence, results_sequence)
+
+
 @pytest.mark.parametrize("ncircuits", (5, 10, 25))
 @pytest.mark.parametrize("executor", (executor_batched, executor_serial))
 def test_run_executor_identical_circuits_batched(ncircuits, executor):