add qasm U gate support

Author: refraction-ray

examples/tcgates.inc

@@ -110,8 +110,4 @@ gate rzz(θ) a, b { cx a, b; rz(θ) b; cx a, b; }
 gate iswap(θ) a, b {cx a, b; h a; cx b, a; phase(θ*π/2) a; cx b, a; phase(-θ*π/2) a; h a; cx a,b; }
 
 // wroot
-gate wroot a {U(π/2, -π/4, π/4) a; }
-
-// to be determined
-// gate r()
-// gate cr() a, b { ctrl @ r() a, b; }
+gate wroot a { U(π/2, -π/4, π/4) a; }

tensorcircuit/abstractcircuit.py

@@ -28,6 +28,8 @@
 vgates = [
     "r",
     "cr",
+    "u",
+    "cu",
     "rx",
     "ry",
     "rz",

tensorcircuit/experimental.py

@@ -258,16 +258,3 @@ def grad_f(*args: Any, **kws: Any) -> Any:
         return grad_values[0]
 
     return grad_f
-
-
-def IBMUgate(theta: float, phi: float, lbd: float) -> Tensor:
-    # not jittable: just for correctness check
-    return np.array(
-        [
-            [np.cos(theta / 2), -np.exp(1.0j * lbd) * np.sin(theta / 2)],
-            [
-                np.exp(1.0j * phi) * np.sin(theta / 2),
-                np.exp(1.0j * (phi + lbd)) * np.cos(theta / 2),
-            ],
-        ]
-    )

tensorcircuit/gates.py

@@ -466,6 +466,41 @@ def phase_gate(theta: float = 0) -> Gate:
     return Gate(unitary)
 
 
+def u_gate(theta: float = 0, phi: float = 0, lbd: float = 0) -> Gate:
+    r"""
+    IBMQ U gate following the converntion of OpenQASM3.0.
+    See `OpenQASM doc <https://openqasm.com/language/gates.html#built-in-gates>`_
+
+    .. math::
+
+        \begin{split}U(\theta,\phi,\lambda) := \left(\begin{array}{cc}
+        \cos(\theta/2) & -e^{i\lambda}\sin(\theta/2) \\
+        e^{i\phi}\sin(\theta/2) & e^{i(\phi+\lambda)}\cos(\theta/2) \end{array}\right).\end{split}
+
+    :param theta: _description_, defaults to 0
+    :type theta: float, optional
+    :param phi: _description_, defaults to 0
+    :type phi: float, optional
+    :param lbd: _description_, defaults to 0
+    :type lbd: float, optional
+    :return: _description_
+    :rtype: Gate
+    """
+    i00, i01, i10, i11 = array_to_tensor(
+        np.array([[1, 0], [0, 0]]),
+        np.array([[0, 1], [0, 0]]),
+        np.array([[0, 0], [1, 0]]),
+        np.array([[0, 0], [0, 1]]),
+    )
+    unitary = (
+        backend.cos(theta / 2) * i00
+        - backend.exp(1.0j * lbd) * backend.sin(theta / 2) * i01
+        + backend.exp(1.0j * phi) * backend.sin(theta / 2) * i10
+        + backend.exp(1.0j * (phi + lbd)) * backend.cos(theta / 2) * i11
+    )
+    return Gate(unitary)
+
+
 def r_gate(theta: float = 0, alpha: float = 0, phi: float = 0) -> Gate:
     r"""
     General single qubit rotation gate
@@ -871,6 +906,7 @@ def mpo_gate(mpo: Operator, name: str = "mpo") -> Operator:
 def meta_vgate() -> None:
     for f in [
         "r",
+        "u",
         "rx",
         "ry",
         "rz",
@@ -886,7 +922,7 @@ def meta_vgate() -> None:
     ]:
         for funcname in [f, f + "gate", f + "_gate"]:
             setattr(thismodule, funcname, GateVF(getattr(thismodule, f + "_gate"), f))
-    for f in ["crx", "cry", "crz"]:
+    for f in ["cu", "crx", "cry", "crz"]:
         for funcname in [f, f + "gate", f + "_gate"]:
             setattr(thismodule, funcname, getattr(thismodule, f[1:]).controlled())
     for f in ["ox", "oy", "oz", "orx", "ory", "orz"]:

tests/test_gates.py

@@ -22,6 +22,15 @@ def test_phase_gate():
     np.testing.assert_allclose(c.state()[1], 0.7071j, atol=1e-4)
 
 
+def test_cu_gate():
+    c = tc.Circuit(2)
+    c.cu(0, 1, theta=np.pi / 2, phi=-np.pi / 4, lbd=np.pi / 4)
+    m = c.matrix()
+    print(m)
+    np.testing.assert_allclose(m[2:, 2:], tc.gates._wroot_matrix, atol=1e-5)
+    np.testing.assert_allclose(m[:2, :2], np.eye(2), atol=1e-5)
+
+
 def test_exp_gate():
     c = tc.Circuit(2)
     c.exp(