Move to method dispatch using act_on for CliffordState, Tableau and ChForm (#3456)

Delete all the now-unneeded methods.

Remaining work: refactor the measurement code

#2948 #2423

Author: smitsanghavi

cirq/sim/clifford/__init__.py

@@ -1,10 +1,3 @@
-from cirq.sim.clifford.clifford_simulator import (
-    CliffordSimulator,
-    CliffordState,
-    CliffordTrialResult,
-    CliffordSimulatorStepResult,
-)
-
 from cirq.sim.clifford.clifford_tableau import (
     CliffordTableau,)
 
@@ -14,8 +7,15 @@
 from cirq.sim.clifford.act_on_stabilizer_ch_form_args import (
     ActOnStabilizerCHFormArgs,)
 
-from cirq.sim.clifford.stabilizer_sampler import (
-    StabilizerSampler,)
-
 from cirq.sim.clifford.stabilizer_state_ch_form import (
     StabilizerStateChForm,)
+
+from cirq.sim.clifford.clifford_simulator import (
+    CliffordSimulator,
+    CliffordState,
+    CliffordTrialResult,
+    CliffordSimulatorStepResult,
+)
+
+from cirq.sim.clifford.stabilizer_sampler import (
+    StabilizerSampler,)

cirq/sim/clifford/clifford_simulator.py

@@ -37,12 +37,10 @@
 
 import cirq
 from cirq import circuits, study, ops, protocols, value
-from cirq.ops import pauli_gates
 from cirq.ops.clifford_gate import SingleQubitCliffordGate
 from cirq.ops.dense_pauli_string import DensePauliString
-from cirq.protocols import unitary
-from cirq.sim import simulator
-from cirq.sim.clifford import clifford_tableau, stabilizer_state_ch_form
+from cirq.protocols import act_on, unitary
+from cirq.sim import clifford, simulator
 from cirq._compat import deprecated, deprecated_parameter
 
 
@@ -277,9 +275,8 @@ def __init__(self, qubit_map, initial_state=0):
         self.qubit_map = qubit_map
         self.n = len(qubit_map)
 
-        self.tableau = clifford_tableau.CliffordTableau(self.n, initial_state)
-        self.ch_form = stabilizer_state_ch_form.StabilizerStateChForm(
-            self.n, initial_state)
+        self.tableau = clifford.CliffordTableau(self.n, initial_state)
+        self.ch_form = clifford.StabilizerStateChForm(self.n, initial_state)
 
     def _json_dict_(self):
         return {
@@ -336,94 +333,18 @@ def wave_function(self):
         return self.state_vector()
 
     def apply_unitary(self, op: 'cirq.Operation'):
-        if len(op.qubits) == 1:
-            self.apply_single_qubit_unitary(op)
-        elif isinstance(op, GlobalPhaseOperation):
-            self.ch_form.omega *= op.coefficient
-        elif op.gate == cirq.CNOT:
-            self.tableau._CNOT(self.qubit_map[op.qubits[0]],
-                               self.qubit_map[op.qubits[1]])
-            self.ch_form._CNOT(self.qubit_map[op.qubits[0]],
-                               self.qubit_map[op.qubits[1]])
-        elif op.gate == cirq.CZ:
-            self.tableau._CZ(self.qubit_map[op.qubits[0]],
-                             self.qubit_map[op.qubits[1]])
-            self.ch_form._CZ(self.qubit_map[op.qubits[0]],
-                             self.qubit_map[op.qubits[1]])
-        else:
+        tableau_args = clifford.ActOnCliffordTableauArgs(
+            self.tableau, [self.qubit_map[i] for i in op.qubits],
+            np.random.RandomState(), {})
+        ch_form_args = clifford.ActOnStabilizerCHFormArgs(
+            self.ch_form, [self.qubit_map[i] for i in op.qubits])
+        try:
+            act_on(op, tableau_args)
+            act_on(op, ch_form_args)
+        except TypeError:
             raise ValueError('%s cannot be run with Clifford simulator.' %
                              str(op.gate))  # type: ignore
-
-    def apply_single_qubit_unitary(self, op: 'cirq.Operation'):
-        qubit = self.qubit_map[op.qubits[0]]
-        if op.gate == cirq.I:
-            return
-
-        if op.gate == cirq.X:
-            self._apply_X(qubit)
-            return
-
-        if op.gate == cirq.Y:
-            self._apply_Y(qubit)
-            return
-
-        if op.gate == cirq.Z:
-            self._apply_Z(qubit)
-            return
-
-        if op.gate == cirq.H:
-            self._apply_H(qubit)
-            return
-
-        u = unitary(op)
-        clifford_gate = SingleQubitCliffordGate.from_unitary(u)
-        if clifford_gate is None:
-            raise ValueError('%s cannot be run with Clifford simulator.' %
-                             str(op.gate))
-
-        h = unitary(ops.H)
-        s = unitary(ops.S)
-        applied_unitary = np.eye(2)
-        for axis, quarter_turns in clifford_gate.decompose_rotation():
-            for _ in range(quarter_turns % 4):
-                if axis == pauli_gates.X:
-                    self._apply_H(qubit)
-                    self._apply_S(qubit)
-                    self._apply_H(qubit)
-                    applied_unitary = h @ s @ h @ applied_unitary
-                elif axis == pauli_gates.Y:
-                    self._apply_S(qubit)
-                    self._apply_S(qubit)
-                    self._apply_H(qubit)
-                    applied_unitary = h @ s @ s @ applied_unitary
-                else:
-                    assert axis == pauli_gates.Z
-                    self._apply_S(qubit)
-                    applied_unitary = s @ applied_unitary
-
-        max_idx = max(np.ndindex(*u.shape), key=lambda t: abs(u[t]))
-        phase_shift = u[max_idx] / applied_unitary[max_idx]
-        self.ch_form.omega *= phase_shift
-
-    def _apply_H(self, qubit: int):
-        self.tableau._H(qubit)
-        self.ch_form._H(qubit)
-
-    def _apply_S(self, qubit: int):
-        self.tableau._S(qubit)
-        self.ch_form._S(qubit)
-
-    def _apply_X(self, qubit: int):
-        self.tableau._X(qubit)
-        self.ch_form._X(qubit)
-
-    def _apply_Z(self, qubit: int):
-        self.tableau._Z(qubit)
-        self.ch_form._Z(qubit)
-
-    def _apply_Y(self, qubit: int):
-        self.tableau._Y(qubit)
-        self.ch_form._Y(qubit)
+        return
 
     @deprecated_parameter(
         deadline='v0.10.0',

cirq/sim/clifford/clifford_tableau.py

@@ -136,35 +136,6 @@ def _str_full_(self) -> str:
 
         return string
 
-    def _CZ(self, q, r):
-        self._H(r)
-        self._CNOT(q, r)
-        self._H(r)
-
-    def _X(self, q):
-        self.rs[:] ^= self.zs[:, q]
-
-    def _Y(self, q):
-        self.rs[:] ^= self.xs[:, q] ^ self.zs[:, q]
-
-    def _Z(self, q):
-        self.rs[:] ^= self.xs[:, q]
-
-    def _S(self, q):
-        self.rs[:] ^= (self.xs[:, q] & self.zs[:, q])
-        self.zs[:, q] ^= self.xs[:, q]
-
-    def _H(self, q):
-        (self.xs[:, q], self.zs[:, q]) = (self.zs[:, q].copy(),
-                                          self.xs[:, q].copy())
-        self.rs[:] ^= (self.xs[:, q] & self.zs[:, q])
-
-    def _CNOT(self, q1, q2):
-        self.rs[:] ^= self.xs[:,q1] & self.zs[:,q2] & \
-            (~(self.xs[:,q2] ^ self.zs[:,q1]))
-        self.xs[:, q2] ^= self.xs[:, q1]
-        self.zs[:, q1] ^= self.zs[:, q2]
-
     def _rowsum(self, q1, q2):
         """Implements the "rowsum" routine defined by
         Aaronson and Gottesman.

cirq/sim/clifford/stabilizer_state_ch_form.py

@@ -17,6 +17,8 @@
 
 import cirq
 from cirq import protocols, value
+from cirq.ops import pauli_gates
+from cirq.sim import clifford
 from cirq.value import big_endian_int_to_digits
 from cirq._compat import deprecated
 
@@ -60,7 +62,8 @@ def __init__(self, num_qubits: int, initial_state: int = 0) -> None:
                                          digit_count=num_qubits,
                                          base=2)):
             if val:
-                self._X(i)
+                protocols.act_on(pauli_gates.X,
+                                 clifford.ActOnStabilizerCHFormArgs(self, [i]))
 
     def _json_dict_(self) -> Dict[str, Any]:
         return protocols.obj_to_dict_helper(
@@ -133,66 +136,23 @@ def state_vector(self) -> np.ndarray:
     def wave_function(self) -> np.ndarray:
         return self.state_vector()
 
-    def _S(self, q):
-        self.M[q, :] ^= self.G[q, :]
-        self.gamma[q] = (self.gamma[q] - 1) % 4
-
     def _S_right(self, q):
         r"""Right multiplication version of S gate."""
         self.M[:, q] ^= self.F[:, q]
         self.gamma[:] = (self.gamma[:] - self.F[:, q]) % 4
 
-    def _Z(self, q):
-        self._S(q)
-        self._S(q)
-
-    def _X(self, q):
-        self._H(q)
-        self._Z(q)
-        self._H(q)
-
-    def _Y(self, q):
-        self._Z(q)
-        self._X(q)
-        self.omega *= 1j
-
-    def _CZ(self, q, r):
-        self.M[q, :] ^= self.G[r, :]
-        self.M[r, :] ^= self.G[q, :]
-
     def _CZ_right(self, q, r):
         r"""Right multiplication version of CZ gate."""
         self.M[:, q] ^= self.F[:, r]
         self.M[:, r] ^= self.F[:, q]
         self.gamma[:] = (self.gamma[:] + 2 * self.F[:, q] * self.F[:, r]) % 4
 
-    def _CNOT(self, q, r):
-        self.gamma[q] = (self.gamma[q] + self.gamma[r] + 2 *
-                         (sum(self.M[q, :] & self.F[r, :]) % 2)) % 4
-        self.G[r, :] ^= self.G[q, :]
-        self.F[q, :] ^= self.F[r, :]
-        self.M[q, :] ^= self.M[r, :]
-
     def _CNOT_right(self, q, r):
         r"""Right multiplication version of CNOT gate."""
         self.G[:, q] ^= self.G[:, r]
         self.F[:, r] ^= self.F[:, q]
         self.M[:, q] ^= self.M[:, r]
 
-    def _H(self, p):
-        t = self.s ^ (self.G[p, :] & self.v)
-        u = self.s ^ (self.F[p, :] & (~self.v)) ^ (self.M[p, :] & self.v)
-
-        alpha = sum(self.G[p, :] & (~self.v) & self.s) % 2
-        beta = sum(self.M[p, :] & (~self.v) & self.s)
-        beta += sum(self.F[p, :] & self.v & self.M[p, :])
-        beta += sum(self.F[p, :] & self.v & self.s)
-        beta %= 2
-
-        delta = (self.gamma[p] + 2 * (alpha + beta)) % 4
-
-        self.update_sum(t, u, delta=delta, alpha=alpha)
-
     def update_sum(self, t, u, delta=0, alpha=0):
         """ Implements the transformation (Proposition 4 in Bravyi et al)