add circuit inverse method

Author: refraction-ray

CHANGELOG.md

@@ -14,6 +14,8 @@
 
 - Add `enable_dlpack` option on interfaces and torchnn
 
+- Add `inverse` method for Circuit (#26)
+
 ### Changed
 
 - Refactor `interfaces` code as a submodule and add pytree support for args

examples/hybrid_gpu_pipeline.py

@@ -76,6 +76,7 @@ def qpreds(x, weights):
     use_jit=True,
     enable_dlpack=True,
 )
+# enable_dlpack = False for old version of ML libs
 
 
 model = torch.nn.Sequential(quantumnet, torch.nn.Linear(9, 1), torch.nn.Sigmoid())

tensorcircuit/circuit.py

@@ -713,6 +713,40 @@ def from_qir(
         c = cls._apply_qir(c, qir)
         return c
 
+    def inverse(self, circuit_params: Optional[Dict[str, Any]] = None) -> "Circuit":
+        """
+        inverse the circuit, return a new inversed circuit
+
+        :EXAMPLE:
+
+        >>> c = tc.Circuit(2)
+        >>> c.H(0)
+        >>> c.rzz(1, 2, theta=0.8)
+        >>> c1 = c.inverse()
+
+        :param circuit_params: keywords dict for initialization the new circuit, defaults to None
+        :type circuit_params: Optional[Dict[str, Any]], optional
+        :return: the inversed circuit
+        :rtype: Circuit
+        """
+        if circuit_params is None:
+            circuit_params = {}
+        if "nqubits" not in circuit_params:
+            circuit_params["nqubits"] = self._nqubits
+
+        c = type(self)(**circuit_params)
+        for d in reversed(self._qir):
+            if "parameters" not in d:
+                c.apply_general_gate_delayed(d["gatef"].adjoint(), d["name"], mpo=d["mpo"])(  # type: ignore
+                    c, *d["index"], split=d["split"]  # type: ignore
+                )
+            else:
+                c.apply_general_variable_gate_delayed(d["gatef"].adjoint(), d["name"], mpo=d["mpo"])(  # type: ignore
+                    c, *d["index"], **d["parameters"], split=d["split"]  # type: ignore
+                )
+
+        return c
+
     def append_from_qir(self, qir: List[Dict[str, Any]]) -> None:
         """
         Apply the ciurict in form of quantum intermediate representation after the current cirucit.

tensorcircuit/gates.py

@@ -13,6 +13,7 @@
 from scipy.stats import unitary_group
 
 from .cons import backend, dtypestr, npdtype
+from .backends import get_backend  # type: ignore
 
 thismodule = sys.modules[__name__]
 
@@ -234,14 +235,25 @@ def __init__(
         self.ctrl = ctrl
 
     def __call__(self, *args: Any, **kws: Any) -> Gate:
+        # m = array_to_tensor(self.m)
+        # m = backend.cast(m, dtypestr)
         m = self.m.astype(npdtype)
         return Gate(deepcopy(m), name=self.n)
 
-    def adjoint(self, *args: Any, **kws: Any) -> "GateF":
-        m = self.__call__(*args, **kws)
-        ma = backend.adjoint(m.tensor)
-        return GateF(ma, self.n + "d", self.ctrl)
-        # TODO(@refraction-ray): adjoint gate convention finally determined
+    def adjoint(self) -> "GateF":
+        m = self.__call__()
+        npb = get_backend("numpy")
+        shape0 = npb.shape_tuple(m.tensor)
+        m0 = npb.reshapem(m.tensor)
+        ma = npb.adjoint(m0)
+        if np.allclose(m0, ma, atol=1e-5):
+            name = self.n
+        else:
+            name = self.n + "d"
+        ma = npb.reshape(ma, shape0)
+        return GateF(ma, name, self.ctrl)
+
+    # TODO(@refraction-ray): adjoint gate convention finally determined
 
     def controlled(self, *args: Any, **kws: Any) -> "GateF":
         def f(*args: Any, **kws: Any) -> Any:
@@ -304,6 +316,22 @@ def __init__(
     def __call__(self, *args: Any, **kws: Any) -> Gate:
         return self.f(*args, **kws)
 
+    def adjoint(self) -> "GateVF":
+        def f(*args: Any, **kws: Any) -> Gate:
+            m = self.__call__(*args, **kws)
+            npb = get_backend("numpy")
+            shape0 = npb.shape_tuple(m.tensor)
+            m0 = npb.reshapem(m.tensor)
+            ma = npb.adjoint(m0)
+            if np.allclose(m0, ma, atol=1e-5):
+                name = self.n
+            else:
+                name = self.n + "d"
+            ma = npb.reshape(ma, shape0)
+            return Gate(ma, name)
+
+        return GateVF(f, self.n + "d", self.ctrl)
+
 
 def meta_gate() -> None:
     """

tests/test_circuit.py

@@ -1017,3 +1017,17 @@ def construct_c(pbc=True):
         m1 = c.expectation_ps(z=[0], enable_lightcone=True)
         m2 = c.expectation_ps(z=[0])
         np.testing.assert_allclose(m1, m2, atol=1e-5)
+
+
+@pytest.mark.parametrize("backend", [lf("npb"), lf("tfb"), lf("jaxb")])
+def test_circuit_inverse(backend):
+    inputs = np.random.uniform(size=[8])
+    inputs /= np.linalg.norm(inputs)
+    c = tc.Circuit(3, inputs=inputs)
+    c.H(1)
+    c.rx(0, theta=0.5)
+    c.cnot(1, 2)
+    c.rzz(0, 2, theta=-0.8)
+    c1 = c.inverse()
+    c.append(c1)
+    np.testing.assert_allclose(c.state(), inputs, atol=1e-5)