Bugfix: change API to modularized cirq package. (#308)

* Refactor circuit build to `cirq_google` module.
* Add check for `cirq_google`, add test.
* 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"
+            pip install "cirq" "qiskit>=0.30" "qulacs" "qibo==0.1.1" "myqlm" "cirq-google"
         fi
         pip install -e .
     - name: Lint with flake8

requirements.txt

@@ -13,6 +13,7 @@ qulacs # default simulator (best integration), remove if the installation gives
 
 #optional quantum backends
 #cirq >= 0.9.2 #
+#cirq_google
 #qiskit>=0.30
 #pyquil<3.0 # you also need to install the forest-sdk
 #qulacs-gpu # you can't have qulacs and qulacs-gpu at the same time

src/tequila/simulators/simulator_cirq.py

@@ -5,10 +5,12 @@
 import sympy
 from tequila.utils import to_float
 
+import importlib
 import numpy as np
 import typing, numbers
 
 import cirq
+import cirq_google
 
 map_1 = lambda x: {'exponent': x}
 map_2 = lambda x: {'exponent': x / np.pi, 'global_shift': -0.5}
@@ -356,35 +358,23 @@ def build_device_circuit(self, ignore_failures=False):
         line = None
         circuit = None
         if isinstance(device, cirq.Device):
-            if isinstance(device, cirq.google.devices.XmonDevice) or isinstance(device,
-                                                                                cirq.google.devices.serializable_device.SerializableDevice):
-                options = ['xmon', 'xmon_partial_cz', 'sqrt_iswap', 'sycamore']
-                if device in [cirq.google.Sycamore, cirq.google.Sycamore23]:
-                    options = ['sycamore', 'sqrt_iswap', 'xmon', 'xmon_partial_cz']
-                for option in options:
-                    try:
-                        line = cirq.google.line_on_device(device, length=len(self.abstract_circuit.qubits))
-
-                        circuit = cirq.google.optimized_for_sycamore(circuit=c, new_device=device,
-                                                                     optimizer_type=option,
-                                                                     qubit_map=lambda q: line[q.x])
-                    except:
-                        line = None
-                        pass
-                if circuit is None:
-                    raise TequilaCirqException('could not optimize for device={}'.format(device))
-
+            HAS_GOOGLE = importlib.util.find_spec('cirq_google')
+            assert HAS_GOOGLE, TequilaCirqException(' cirq_google package is not installed.')
+
+            if device in [cirq_google.Sycamore, cirq_google.Sycamore23]:
+                try:
+                    circuit = cirq.optimize_for_target_gateset(circuit=c, gateset=cirq_google.SycamoreTargetGateset())
+                except ValueError as E:
+                    original_message = str(E)
+                    raise TequilaCirqException('original message:\n{}\n\ncould not optimize for device={}'.format(original_message,device))
             else:
                 ### under construction (potentially on other branches)
-                raise TequilaException('Only known and Xmon devices currently functional. Sorry!')
+                raise TequilaException('Only Sycamore and Sycamore23 devices currently functional. Sorry!')
+
         else:
             raise TequilaException(
                 'build_device_circuit demands a cirq.Device object; received {}, of type {}'.format(str(device),
                                                                                                     type(device)))
-
-        if line is not None:
-            for k in self.qubit_map.keys():
-                self.qubit_map[k].instance = line[self.qubit_map[k].instance.x]
         return circuit
 
     def build_noisy_circuit(self, noise):
@@ -447,7 +437,7 @@ def retrieve_device(self, device):
             the device on which to execute cirq circuits.
         """
         if isinstance(device, str):
-            return getattr(cirq.google, device)
+            return getattr(cirq_google, device)
         else:
             if device is None:
                 return device
@@ -474,7 +464,7 @@ def check_device(self, device):
             return
         else:
             assert isinstance(device, str)
-            if device.lower() in ['foxtail', 'sycamore', 'sycamore23', 'bristlecone']:
+            if device.lower() in ['sycamore', 'sycamore23']:
                 pass
             else:
                 raise TequilaException('requested device {} could not be found!'.format(device))

tests/test_simulator_backends.py

@@ -2,6 +2,7 @@
 All Backends need to be installed for full testing
 """
 
+import importlib
 import numpy
 import pytest
 import random
@@ -16,6 +17,20 @@
 import os, glob
 
 
+HAS_GOOGLE = importlib.util.find_spec('cirq_google')
+@pytest.mark.skipif(condition=HAS_GOOGLE, reason="cirq_google not installed")
+def test_cirq_google_devices():
+    import cirq_google
+
+    U = tq.paulis.X(0)
+    U += tq.gates.Givens(0, 1, angle=numpy.pi/4)    # Givens rotation with angle = pi/4 gives 1/sqrt(2)|01> + 1/sqrt(2)|10> (up to a phase factor).
+    wfn = tq.simulate(U, device="Sycamore", backend="cirq")
+    wfnx0 = tq.simulate(tq.paulis.X(0))
+    assert numpy.isclose(numpy.abs(wfn.inner(wfnx0))**2, 0.5)
+    wfnx1 = tq.simulate(tq.paulis.X(1))
+    assert numpy.isclose(numpy.abs(wfn.inner(wfnx1))**2, 0.5)
+
+
 def teardown_function(function):
     [os.remove(x) for x in glob.glob("*.npy")]
     [os.remove(x) for x in glob.glob("qvm.log")]