ADD:

1. has `constexpr` variable `pre_defined_qgates`
2. has `struct` `qgate` with `type` and `matrix` field
3. has an `enum` with different types of quantum gates in it
4. using `std::complex<double>` as a universal data type in this project

Author: Dark-CodeX

qubitverse/simulator/gates/gates.hh

@@ -0,0 +1,56 @@
+/**
+ * @file gates.hh
+ * @license This file is licensed under the GNU GENERAL PUBLIC LICENSE Version 3, 29 June 2007. You may obtain a copy of this license at https://www.gnu.org/licenses/gpl-3.0.en.html.
+ * @author Tushar Chaurasia (Dark-CodeX)
+ */
+
+#ifndef SIMULATOR_GATES
+#define SIMULATOR_GATES
+
+#include <complex>
+#include <cmath> // for sqrt and M_PI
+
+namespace simulator
+{
+    using complex = std::complex<double>;
+    using namespace std::complex_literals;
+
+    enum gates : unsigned char
+    {
+        IDENTITY, // identity-gate
+        PAULI_X,  // NOT-gate
+        PAULI_Y,
+        PAULI_Z,          // Phase Flip gate
+        HADAMARD,         // H-gate
+        PHASE_PI_2_SHIFT, // pi/2 phase shift
+        PHASE_PI_4_SHIFT, // pi/4 phase shift
+        PHASE_GENERAL_SHIFT,
+        ROTATION_X,
+        ROTATION_Y,
+        ROTATION_Z
+    };
+
+    struct qgate
+    {
+        gates type;
+        complex matrix[2][2]; // 2x2 matrix that stores various types of gates
+    };
+
+    inline const constexpr qgate pre_defined_qgates[7] = {
+        {IDENTITY, {{1, 0}, {0, 1}}},
+        {PAULI_X, {{0, 1}, {1, 0}}},
+        {PAULI_Y, {{0, {0, -1}}, {{0, 1}, 0}}},
+        {PAULI_Z, {{1, 0}, {0, -1}}},
+        {HADAMARD, {{1.0 / M_SQRT2, 1.0 / M_SQRT2}, {1.0 / M_SQRT2, -1.0 / M_SQRT2}}},
+        {PHASE_PI_2_SHIFT, {{1, 0}, {0, {0, 1}}}},                // e^(i * pi/2) = i
+        {PHASE_PI_4_SHIFT, {{1, 0}, {0, {M_SQRT1_2, M_SQRT1_2}}}} // e^(i * pi/4) = (sqrt(2)/2) + i(sqrt(2)/2)
+    };
+
+    void apply_predefined_gate(const enum gates &__g_type, complex (&__s)[2]);
+
+    qgate &get_theta_gates(qgate &__g, const enum gates &__g_type, const double &theta);
+
+    void apply_theta_gates(const enum gates &__g_type, complex (&__s)[2], const double &theta);
+}
+
+#endif