Merge pull request #305 from quantumlib/add-cirq-channels

Add Cirq channels.

lib/BUILD

@@ -8,6 +8,9 @@ cc_library(
     hdrs = [
         "bits.h",
         "bitstring.h",
+        "channel.h",
+        "channels_cirq.h",
+        "circuit_noisy.h",
         "circuit_qsim_parser.h",
         "circuit.h",
         "expect.h",
@@ -395,12 +398,42 @@ cc_library(
     ],
 )
 
+### Channel and noisy circuit libraries ###
+
+cc_library(
+    name = "channel",
+    hdrs = ["channel.h"],
+    deps = [":gate"],
+)
+
+cc_library(
+    name = "circuit_noisy",
+    hdrs = ["circuit_noisy.h"],
+    deps = [
+        ":channel",
+        ":circuit",
+    ],
+)
+
+cc_library(
+    name = "channels_cirq",
+    hdrs = ["channels_cirq.h"],
+    deps = [
+        ":channel",
+        ":gates_cirq",
+    ],
+)
+
 ### Quantum trajectory simulator ###
 
 cc_library(
     name = "qtrajectory",
     hdrs = ["qtrajectory.h"],
-    deps = [":gate"],
+    deps = [
+        ":circuit_noisy",
+        ":gate",
+        ":gate_appl",
+    ],
 )
 
 ### UnitarySpace libraries ###

lib/channel.h

@@ -0,0 +1,81 @@
+// Copyright 2019 Google LLC. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef CHANNEL_H_
+#define CHANNEL_H_
+
+#include "gate.h"
+
+namespace qsim {
+
+/**
+ * Kraus operator.
+ */
+template <typename Gate>
+struct KrausOperator {
+  enum Kind {
+    kNormal = 0,
+    kMeasurement = gate::kMeasurement,
+  };
+
+  /**
+   * Kraus operator type;
+   */
+  Kind kind;
+
+  /**
+   * If true, the Kraus operator is a unitary operator times a constant.
+   */
+  bool unitary;
+
+  /**
+   * Lower bound on Kraus operator probability.
+   */
+  double prob;
+
+  /**
+   * Sequence of operations that represent the Kraus operator. This can be just
+   * one operation.
+   */
+  std::vector<Gate> ops;
+};
+
+/**
+ * Quantum channel.
+ */
+template <typename Gate>
+using Channel = std::vector<KrausOperator<Gate>>;
+
+/**
+ * Makes a channel from the gate.
+ * @param time The time to place the channel at.
+ * @param gate The input gate.
+ * @return The output channel.
+ */
+template <typename Gate>
+Channel<Gate> MakeChannelFromGate(unsigned time, const Gate& gate) {
+  auto normal = KrausOperator<Gate>::kNormal;
+  auto measurement = KrausOperator<Gate>::kMeasurement;
+
+  auto kind = gate.kind == gate::kMeasurement ? measurement : normal;
+
+  Channel<Gate> channel = {{kind, true, 1, {gate}}};
+  channel[0].ops[0].time = time;
+
+  return channel;
+}
+
+}  // namespace qsim
+
+#endif  // CHANNEL_H_