Merge pull request #368 from ohuettenhofer/fix_qiskit

* Fix current Qiskit versions

* Update ci_backends.yml

.github/workflows/ci_backends.yml

@@ -32,7 +32,7 @@ jobs:
             # myqlm does not work in python3.7
             pip install "cirq" "qiskit>=0.30" "qulacs" "qibo==0.1.1"
         elif [ $ver -eq 8 ]; then
-            pip install "cirq" "qiskit>=0.30" "qulacs" "qibo==0.1.1" "myqlm" "cirq-google"
+            pip install "cirq" "qiskit" "qulacs" "qibo==0.1.1" "myqlm" "cirq-google"
         fi
         pip install -e .
     - name: Lint with flake8

README.md

@@ -342,12 +342,7 @@ You can avoid it by downgrading cirq and openfermion
 ```bash
 pip install --upgrade "openfermion<=1.0.0"
 pip install --upgrade "cirq<=0.9.1"
-```  
-
-
-## Qiskit backend
-Qiskit version 0.25 is not yet supported.
-`pip install --upgrade qiskit<0.25` fixes potential issues. If not: Please let us know.
+```
 
 ## Circuit drawing
 Standard graphical circuit representation within a Jupyter environment is often done using `tq.draw`.

src/tequila/simulators/simulator_qiskit.py

@@ -1,22 +1,26 @@
 from tequila.simulators.simulator_base import BackendCircuit, QCircuit, BackendExpectationValue
+from tequila.utils.bitstrings import reverse_int_bits
 from tequila.wavefunction.qubit_wavefunction import QubitWaveFunction
 from tequila import TequilaException, TequilaWarning
 from tequila import BitString, BitNumbering, BitStringLSB
 from tequila.utils.keymap import KeyMapRegisterToSubregister
 from tequila.utils import to_float
-import qiskit, numpy, warnings
+import warnings
+import numpy as np
+import qiskit, qiskit_aer, qiskit.providers.fake_provider
 
-HAS_NOISE=True
+HAS_NOISE = True
 try:
-    from qiskit_aer import noise as qiskitnoise
+    from qiskit_aer import noise as qiskitnoise, AerSimulator
 except:
     HAS_NOISE = False
 
-HAS_IBMQ=True
+HAS_IBMQ = True
 try:
-    from qiskit.providers.ibmq import IBMQBackend
+    from qiskit_ibm_runtime import IBMBackend
 except:
-    HAS_IBMQ=False
+    HAS_IBMQ = False
+
 
 def get_bit_flip(p):
     """
@@ -70,16 +74,24 @@ def get_phase_flip(p):
     'multicontrol': 3
 }
 
-full_basis = ['x', 'y', 'z', 'id', 'u1', 'u2', 'u3', 'h','unitary','sx',
+full_basis = ['x', 'y', 'z', 'id', 'u1', 'u2', 'u3', 'h', 'unitary', 'sx',
               'cx', 'cy', 'cz', 'cu3', 'ccx']
 
+
 def qiskit_device_dict():
-    devices = {}
-    devices.update({str(x).lower():x for x in qiskit.Aer.backends()})
-    devices.update({str(x).lower():x for x in qiskit.test.mock.FakeProvider().backends()})
+    # As of Quiskit Aer 0.15.0, backends() also returns legacy backends which are not AerSimulators that will be
+    # deprecated in the future
+    # TODO: Instead of building a dict with all backends just to search it, search directly with `get_backend`
+    # https://qiskit.github.io/qiskit-aer/stubs/qiskit_aer.AerProvider.html#qiskit_aer.AerProvider.get_backend
+    devices = {backend.name.lower(): backend for backend in qiskit_aer.AerProvider().backends()
+               if isinstance(backend, AerSimulator)}
+
+    # FakeProvider has been removed, see https://github.com/Qiskit/qiskit/issues/10954
+    # devices.update({str(x).lower(): x for x in qiskit.test.mock.FakeProvider().backends()})
 
     return devices
 
+
 class TequilaQiskitException(TequilaException):
     def __str__(self):
         return "Error in qiskit backend:" + self.message
@@ -125,6 +137,8 @@ class BackendCircuitQiskit(BackendCircuit):
         transform a tequila NoiseModel into a qiskit noise model.
 
     """
+    STATEVECTOR_DEVICE_NAME = "aer_simulator_statevector"
+
     compiler_arguments = {
         "trotterized": True,
         "swap": False,
@@ -145,7 +159,7 @@ class BackendCircuitQiskit(BackendCircuit):
     }
 
     numbering = BitNumbering.LSB
-            
+
     def __init__(self, abstract_circuit: QCircuit, variables, qubit_map=None, noise=None,
                  device=None, *args, **kwargs):
         """
@@ -188,8 +202,9 @@ def __init__(self, abstract_circuit: QCircuit, variables, qubit_map=None, noise=
         if qubit_map is None:
             qubit_map = {q: i for i, q in enumerate(abstract_circuit.qubits)}
         else:
-            warnings.warn("reveived custom qubit_map = {}\n"
-                          "This is not fully integrated with qiskit and might result in unexpected behaviour".format(qubit_map), TequilaWarning)
+            warnings.warn(f"reveived custom qubit_map = {qubit_map}\n"
+                          "This is not fully integrated with qiskit and might result in unexpected behaviour",
+                          TequilaWarning)
 
         n_qubits = max(qubit_map.values()) + 1
 
@@ -201,7 +216,7 @@ def __init__(self, abstract_circuit: QCircuit, variables, qubit_map=None, noise=
 
         self.classical_map = self.make_classical_map(qubit_map=self.qubit_map)
 
-        if noise != None:
+        if noise is not None:
             self.noise_lookup = {
                 'phase damp': qiskitnoise.phase_damping_error,
                 'amplitude damp': qiskitnoise.amplitude_damping_error,
@@ -211,12 +226,12 @@ def __init__(self, abstract_circuit: QCircuit, variables, qubit_map=None, noise=
                 'depolarizing': qiskitnoise.depolarizing_error
             }
 
-            if isinstance(noise, str): #string noise means "use the same noise as the device I tell you to get."
+            if isinstance(noise, str):  # string noise means "use the same noise as the device I tell you to get."
                 try:
                     self.check_device(noise)
                     self.noise_model = qiskitnoise.NoiseModel.from_backend(noise)
                 except TequilaQiskitException:
-                    raise TequilaException("noise init from string requires that noise names a device. Got {}".format(noise))
+                    raise TequilaException(f"noise init from string requires that noise names a device. Got {noise}")
 
             else:
                 self.noise_model = self.noise_model_converter(noise)
@@ -235,7 +250,7 @@ def make_qubit_map(self, qubits: dict = None):
         qubit_map = super().make_qubit_map(qubits=qubits)
         mapped_qubits = [q.number for q in qubit_map.values()]
         for k, v in qubit_map.items():
-            qubit_map[k].instance = self.q [v.number]
+            qubit_map[k].instance = self.q[v.number]
 
         return qubit_map
 
@@ -266,10 +281,12 @@ def do_simulate(self, variables, initial_state=0, *args, **kwargs) -> QubitWaveF
         """
         if self.noise_model is None:
             if self.device is None:
-                qiskit_backend = self.retrieve_device('statevector_simulator')
+                qiskit_backend = self.retrieve_device(self.STATEVECTOR_DEVICE_NAME)
             else:
                 if 'statevector' not in str(self.device):
-                    raise TequilaException('For simulation, only state vector simulators are supported; recieved device={}, you might have forgoten to set the samples keyword - e.g. (device={}, samples=1000). If not set, tequila assumes that full wavefunction simualtion is demanded which is not compatible with qiskit devices or fake devices except for device=statevector'.format(self.device, self.device))
+                    raise TequilaException(
+                        'For simulation, only state vector simulators are supported; recieved device={}, you might have forgoten to set the samples keyword - e.g. (device={}, samples=1000). If not set, tequila assumes that full wavefunction simualtion is demanded which is not compatible with qiskit devices or fake devices except for device=statevector'.format(
+                            self.device, self.device))
                 else:
                     qiskit_backend = self.retrieve_device(self.device)
         else:
@@ -279,22 +296,24 @@ def do_simulate(self, variables, initial_state=0, *args, **kwargs) -> QubitWaveF
         if "optimization_level" in kwargs:
             optimization_level = kwargs['optimization_level']
 
-        opts = {}
+        circuit = self.circuit.assign_parameters(self.resolver)
+
         if initial_state != 0:
-            array = numpy.zeros(shape=[2 ** self.n_qubits])
-            i = BitStringLSB.from_binary(BitString.from_int(integer=initial_state, nbits=self.n_qubits).binary)
-            print(initial_state, " -> ", i)
-            array[i.integer] = 1.0
-            opts = {"initial_statevector": array}
+            state = np.zeros(2 ** self.n_qubits)
+            initial_state = reverse_int_bits(initial_state, self.n_qubits)
+            state[initial_state] = 1.0
+            init_circuit = qiskit.QuantumCircuit(self.q, self.c)
+            init_circuit.set_statevector(state)
+            circuit = init_circuit.compose(circuit)
 
-        circuit = self.circuit.bind_parameters(self.resolver)
+        circuit.save_statevector()
 
-        qiskit_job = qiskit_backend.run(circuit,optimization_level=optimization_level,**opts)
+        backend_result = qiskit_backend.run(circuit, optimization_level=optimization_level).result()
 
-        backend_result = qiskit_job.result()
         return QubitWaveFunction.from_array(arr=backend_result.get_statevector(circuit), numbering=self.numbering)
 
-    def do_sample(self, circuit: qiskit.QuantumCircuit, samples: int, read_out_qubits, *args, **kwargs) -> QubitWaveFunction:
+    def do_sample(self, circuit: qiskit.QuantumCircuit, samples: int, read_out_qubits, *args,
+                  **kwargs) -> QubitWaveFunction:
         """
         Helper function for performing sampling.
         Parameters
@@ -319,17 +338,18 @@ def do_sample(self, circuit: qiskit.QuantumCircuit, samples: int, read_out_qubit
         else:
             qiskit_backend = self.retrieve_device(self.device)
 
-        if isinstance(qiskit_backend,IBMQBackend):
+        if isinstance(qiskit_backend, IBMBackend):
             if self.noise_model is not None:
-                raise TequilaException('Cannot combine backend {} with custom noise models.'.format(str(qiskit_backend)))
-            circuit = circuit.bind_parameters(self.resolver)  # this is necessary in spite of qiskit "fixing" it
+                raise TequilaException(
+                    'Cannot combine backend {} with custom noise models.'.format(str(qiskit_backend)))
+            circuit = circuit.assign_parameters(self.resolver)  # this is necessary in spite of qiskit "fixing" it
             circuit = qiskit.transpile(circuit, qiskit_backend)
-            return self.convert_measurements(qiskit_backend.run(circuit,shots=samples,
-                                                            optimization_level=optimization_level),
+            return self.convert_measurements(qiskit_backend.run(circuit, shots=samples,
+                                                                optimization_level=optimization_level),
                                              target_qubits=read_out_qubits)
         else:
-            if isinstance(qiskit_backend, qiskit.test.mock.FakeBackend):
-                circuit = circuit.bind_parameters(self.resolver)  # this is necessary in spite of qiskit "fixing" it
+            if isinstance(qiskit_backend, qiskit.providers.fake_provider.FakeBackend):
+                circuit = circuit.assign_parameters(self.resolver)  # this is necessary in spite of qiskit "fixing" it
                 coupling_map = qiskit_backend.configuration().coupling_map
                 from_back = qiskitnoise.NoiseModel.from_backend(qiskit_backend)
                 if self.noise_model is not None:
@@ -343,15 +363,15 @@ def do_sample(self, circuit: qiskit.QuantumCircuit, samples: int, read_out_qubit
                                            optimization_level=optimization_level
                                            )
 
-                job=qiskit_backend.run(circuit, shots=samples)
-                return self.convert_measurements(job,target_qubits=read_out_qubits)
+                job = qiskit_backend.run(circuit, shots=samples)
+                return self.convert_measurements(job, target_qubits=read_out_qubits)
             else:
                 if self.noise_model is not None:
                     qiskit_backend.set_options(noise_model=self.noise_model)  # fits better with our methodology.
                     use_basis = full_basis
                 else:
                     use_basis = qiskit_backend.configuration().basis_gates
-                circuit = circuit.bind_parameters(self.resolver)  # this is necessary -- see qiskit-aer issue 1346
+                circuit = circuit.assign_parameters(self.resolver)  # this is necessary -- see qiskit-aer issue 1346
                 circuit = qiskit.transpile(circuit, backend=qiskit_backend,
                                            basis_gates=use_basis,
                                            optimization_level=optimization_level
@@ -436,7 +456,8 @@ def add_parametrized_gate(self, gate, circuit, *args, **kwargs):
             par = float(gate.parameter)
         if gate.is_controlled():
             if len(gate.control) > 2:
-                raise TequilaQiskitException("multi-controls beyond 2 not yet supported for the qiskit backend. Gate was:\n{}".format(gate) )
+                raise TequilaQiskitException(
+                    "multi-controls beyond 2 not yet supported for the qiskit backend. Gate was:\n{}".format(gate))
             ops[1](circuit)(par, self.qubit(gate.control[0]), self.qubit(gate.target[0]))
         else:
             ops[0](circuit)(par, self.qubit(gate.target[0]))
@@ -590,7 +611,7 @@ def check_device(self, device):
         if device is None:
             return
 
-        elif isinstance(device,qiskit.providers.Backend):
+        elif isinstance(device, qiskit.providers.Backend):
             return
 
         elif isinstance(device, dict):

src/tequila/utils/bitstrings.py

@@ -178,7 +178,7 @@ def numbering(self) -> BitNumbering:
         return BitNumbering.LSB
 
 
-def _reverse_int_bits(x: int, nbits: int) -> int:
+def reverse_int_bits(x: int, nbits: int) -> int:
     if nbits is None:
         nbits = x.bit_length()
     assert nbits <= 32
@@ -193,7 +193,7 @@ def _reverse_int_bits(x: int, nbits: int) -> int:
 
 def initialize_bitstring(integer: int, nbits: int = None, numbering_in: BitNumbering = BitNumbering.MSB,
                          numbering_out: BitNumbering = BitNumbering.MSB):
-    integer = _reverse_int_bits(integer, nbits) if numbering_in != numbering_out else integer
+    integer = reverse_int_bits(integer, nbits) if numbering_in != numbering_out else integer
     if numbering_out == BitNumbering.MSB:
         return BitString.from_int(integer=integer, nbits=nbits)
     else: