update

unitary/alpha/quantum_world.py

@@ -305,6 +305,27 @@ def _interpret_result(self, result: Union[int, Iterable[int]]) -> int:
             return result_list[0]
         return result
 
+    def unhook(self, object: QuantumObject) -> None:
+        """Replace all usages of the given `object` in the circuit with a new ancilla,
+        so that
+         - all former operations on `object` will be applied on the new ancilla;
+         - future operations on `object` start with its new reset value.
+
+        Note that we don't do force measurement on it, since we don't care about its
+        current value but just want to reset it.
+        """
+        # Create a new ancilla.
+        new_ancilla = self._add_ancilla(object.name)
+        # Replace operations of the given `object` with the new ancilla.
+        qubit_remapping_dict = {
+            object.qubit: new_ancilla.qubit,
+            new_ancilla.qubit: object.qubit,
+        }
+        self.circuit = self.circuit.transform_qubits(
+            lambda q: qubit_remapping_dict.get(q, q)
+        )
+        return
+
     def force_measurement(
         self, obj: QuantumObject, result: Union[enum.Enum, int]
     ) -> None:

unitary/alpha/quantum_world_test.py

@@ -176,7 +176,7 @@ def test_pop(simulator, compile_to_qubits):
         compile_to_qubits=compile_to_qubits,
     )
     alpha.Split()(light, light2, light3)
-    results = board.peek([light2, light3], count=200)
+    results = board.peek([light2, light3], count=200, convert_to_enum=False)
     assert all(result[0] != result[1] for result in results)
     assert not all(result[0] == 0 for result in results)
     assert not all(result[0] == 1 for result in results)
@@ -189,6 +189,26 @@ def test_pop(simulator, compile_to_qubits):
     assert all(result[1] != popped for result in results)
 
 
+@pytest.mark.parametrize("compile_to_qubits", [False, True])
+@pytest.mark.parametrize("simulator", [cirq.Simulator, alpha.SparseSimulator])
+def test_unhook(simulator, compile_to_qubits):
+    light = alpha.QuantumObject("l1", Light.GREEN)
+    light2 = alpha.QuantumObject("l2", Light.RED)
+    light3 = alpha.QuantumObject("l3", Light.RED)
+    board = alpha.QuantumWorld(
+        [light, light2, light3],
+        sampler=simulator(),
+        compile_to_qubits=compile_to_qubits,
+    )
+    alpha.Split()(light, light2, light3)
+    board.unhook(light2)
+    results = board.peek([light2, light3], count=200, convert_to_enum=False)
+    print(results)
+    assert all(result[0] == 0 for result in results)
+    assert not all(result[1] == 0 for result in results)
+    assert not all(result[1] == 1 for result in results)
+
+
 # TODO: Consider moving to qudit_effects.py if this can be broadly useful.
 class QuditSwapEffect(alpha.QuantumEffect):
     def __init__(self, dimension):

unitary/examples/quantum_chinese_chess/board.py

@@ -49,7 +49,7 @@ def from_fen(cls, fen: str = _INITIAL_FEN) -> "Board":
         FEN rule for Chinese Chess could be found at https://www.wxf-xiangqi.org/images/computer-xiangqi/fen-for-xiangqi-chinese-chess.pdf
         """
         chess_board = {}
-        row_index = 9
+        row_index = 0
         king_locations = []
         pieces, turns = fen.split(" ", 1)
         for row in pieces.split("/"):
@@ -74,15 +74,11 @@ def from_fen(cls, fen: str = _INITIAL_FEN) -> "Board":
                         name, SquareState.OCCUPIED, piece_type, color
                     )
                     col += 1
-            row_index -= 1
+            row_index += 1
         board = alpha.QuantumWorld(chess_board.values())
         # Here 0 means the player RED while 1 the player BLACK.
         current_player = 0 if "w" in turns else 1
         # TODO(): maybe add check to make sure the input fen itself is correct.
-        if len(king_locations) != 2:
-            raise ValueError(
-                f"We expect two KINGs on the board, but got {len(king_locations)}."
-            )
         return cls(board, current_player, king_locations)
 
     def __str__(self):
@@ -92,7 +88,7 @@ def __str__(self):
         for col in "abcdefghi":
             board_string.append(f" {col}")
         board_string.append("\n")
-        for row in range(num_rows):
+        for row in range(num_rows - 1, -1, -1):
             # Print the row index on the left.
             board_string.append(f"{row} ")
             for col in "abcdefghi":
@@ -165,7 +161,7 @@ def path_pieces(self, source: str, target: str) -> Tuple[List[str], List[str]]:
         elif abs(dy) == 2 and abs(dx) == 1:
             pieces.append(f"{chr(x0)}{y0 + dy_sign}")
         else:
-            raise ValueError("Unexpected input to path_pieces().")
+            raise ValueError("The input move is illegal.")
         for piece in pieces:
             if self.board[piece].is_entangled:
                 quantum_pieces.append(piece)
@@ -188,3 +184,15 @@ def flying_general_check(self) -> bool:
             # If there are no pieces between two KINGs, the check successes. Game ends.
             return True
         # TODO(): add check when there are quantum pieces in between.
+
+    def sample(self, repetitions: int) -> List[int]:
+        """Sample the current board by the given `repetitions`.
+        Returns a list of 90-bit bitstring, each corresponding to one sample.
+        """
+        samples = self.board.peek(count=repetitions, convert_to_enum=False)
+        # Convert peek results (in List[List[int]]) into List[int].
+        samples = [
+            int("0b" + "".join([str(i) for i in sample[::-1]]), base=2)
+            for sample in samples
+        ]
+        return samples

unitary/examples/quantum_chinese_chess/board_test.py

@@ -28,16 +28,16 @@ def test_init_with_default_fen():
         board.__str__()
         == """
   a b c d e f g h i
-0 r h e a k a e h r  0
-1 . . . . . . . . .  1
-2 . c . . . . . c .  2
-3 p . p . p . p . p  3
-4 . . . . . . . . .  4
-5 . . . . . . . . .  5
-6 P . P . P . P . P  6
-7 . C . . . . . C .  7
+9 r h e a k a e h r  9
 8 . . . . . . . . .  8
-9 R H E A K A E H R  9
+7 . c . . . . . c .  7
+6 p . p . p . p . p  6
+5 . . . . . . . . .  5
+4 . . . . . . . . .  4
+3 P . P . P . P . P  3
+2 . C . . . . . C .  2
+1 . . . . . . . . .  1
+0 R H E A K A E H R  0
   a b c d e f g h i
 """
     )
@@ -47,21 +47,21 @@ def test_init_with_default_fen():
         board.__str__()
         == """
 　ａｂｃｄｅｆｇｈｉ
-０車馬相仕帥仕相馬車０
-１．．．．．．．．．１
-２．砲．．．．．砲．２
-３卒．卒．卒．卒．卒３
-４．．．．．．．．．４
-５．．．．．．．．．５
-６兵．兵．兵．兵．兵６
-７．炮．．．．．炮．７
+９車馬相仕帥仕相馬車９
 ８．．．．．．．．．８
-９车马象士将士象马车９
+７．砲．．．．．砲．７
+６卒．卒．卒．卒．卒６
+５．．．．．．．．．５
+４．．．．．．．．．４
+３兵．兵．兵．兵．兵３
+２．炮．．．．．炮．２
+１．．．．．．．．．１
+０车马象士将士象马车０
 　ａｂｃｄｅｆｇｈｉ
 """
     )
 
-    assert board.king_locations == ["e9", "e0"]
+    assert board.king_locations == ["e0", "e9"]
 
 
 def test_init_with_specified_fen():
@@ -71,16 +71,16 @@ def test_init_with_specified_fen():
         board.__str__()
         == """
   a b c d e f g h i
-0 . . . A K . . . c  0
-1 . . . . A p . r .  1
-2 . . . . . . . . .  2
-3 . . . . . . . . .  3
-4 . . . . . . . . .  4
+9 . . . A K . . . c  9
+8 . . . . A p . r .  8
+7 . . . . . . . . .  7
+6 . . . . . . . . .  6
 5 . . . . . . . . .  5
-6 . . . . . . . H .  6
-7 . . . h R . . . .  7
-8 . . . . a . . . .  8
-9 . . . . k a R . .  9
+4 . . . . . . . . .  4
+3 . . . . . . . H .  3
+2 . . . h R . . . .  2
+1 . . . . a . . . .  1
+0 . . . . k a R . .  0
   a b c d e f g h i
 """
     )
@@ -90,21 +90,21 @@ def test_init_with_specified_fen():
         board.__str__()
         == """
 　ａｂｃｄｅｆｇｈｉ
-０．．．士将．．．砲０
-１．．．．士卒．車．１
-２．．．．．．．．．２
-３．．．．．．．．．３
-４．．．．．．．．．４
+９．．．士将．．．砲９
+８．．．．士卒．車．８
+７．．．．．．．．．７
+６．．．．．．．．．６
 ５．．．．．．．．．５
-６．．．．．．．马．６
-７．．．馬车．．．．７
-８．．．．仕．．．．８
-９．．．．帥仕车．．９
+４．．．．．．．．．４
+３．．．．．．．马．３
+２．．．馬车．．．．２
+１．．．．仕．．．．１
+０．．．．帥仕车．．０
 　ａｂｃｄｅｆｇｈｉ
 """
     )
 
-    assert board.king_locations == ["e9", "e0"]
+    assert board.king_locations == ["e0", "e9"]
 
 
 def test_path_pieces():