{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "59ea7797",
   "metadata": {},
   "source": [
    "# 05 - Multi-Qubit Gates\n",
    "\n",
    "Explore two-qubit and three-qubit gates: CNOT, CZ, SWAP, Toffoli, Fredkin, and more.\n",
    "\n",
    "**Concepts:** Controlled gates, SWAP family, Toffoli, Fredkin"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f40bef98",
   "metadata": {},
   "outputs": [],
   "source": [
    "import quantsdk as qs\n",
    "import math"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "8058c63d",
   "metadata": {},
   "source": [
    "## CNOT (CX) — The Entanglement Gate"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b2aa79be",
   "metadata": {},
   "outputs": [],
   "source": [
    "# CNOT flips target when control is |1>\n",
    "for ctrl_state in ['0', '1']:\n",
    "    circuit = qs.Circuit(2)\n",
    "    if ctrl_state == '1':\n",
    "        circuit.x(0)  # Set control to |1>\n",
    "    circuit.cx(0, 1).measure_all()\n",
    "    result = qs.run(circuit, shots=100, seed=42)\n",
    "    print(f\"CNOT with control={ctrl_state}: {result.counts}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d81fb2de",
   "metadata": {},
   "source": [
    "## Controlled Gates (CY, CZ, CH, CS, CSX)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "9ae8c10a",
   "metadata": {},
   "outputs": [],
   "source": [
    "controlled_gates = [\n",
    "    (\"CY\",  lambda c: c.cy(0, 1)),\n",
    "    (\"CZ\",  lambda c: c.cz(0, 1)),\n",
    "    (\"CH\",  lambda c: c.ch(0, 1)),\n",
    "    (\"CS\",  lambda c: c.cs(0, 1)),\n",
    "    (\"CSX\", lambda c: c.csx(0, 1)),\n",
    "]\n",
    "\n",
    "print(\"Controlled gates with control=|1>:\")\n",
    "for name, apply_gate in controlled_gates:\n",
    "    circuit = qs.Circuit(2)\n",
    "    circuit.x(0)  # Set control to |1>\n",
    "    apply_gate(circuit)\n",
    "    circuit.measure_all()\n",
    "    result = qs.run(circuit, shots=1000, seed=42)\n",
    "    print(f\"  {name:4s}: {result.counts}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "da9e5015",
   "metadata": {},
   "source": [
    "## Controlled Rotations (CRX, CRY, CRZ, CP)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "47510dc6",
   "metadata": {},
   "outputs": [],
   "source": [
    "# CRY with control=|1>\n",
    "for theta in [0, math.pi/4, math.pi/2, math.pi]:\n",
    "    circuit = qs.Circuit(2).x(0).cry(0, 1, theta).measure_all()\n",
    "    result = qs.run(circuit, shots=1000, seed=42)\n",
    "    p_target_1 = sum(c for bs, c in result.counts.items() if bs[1] == '1') / 1000\n",
    "    print(f\"CRY(theta={theta:.2f}): P(target=|1>) = {p_target_1:.3f}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "863667ee",
   "metadata": {},
   "source": [
    "## SWAP Gate Family"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "6951725f",
   "metadata": {},
   "outputs": [],
   "source": [
    "# SWAP: exchanges qubit states\n",
    "circuit = qs.Circuit(2).x(0).swap(0, 1).measure_all()  # |10> -> |01>\n",
    "result = qs.run(circuit, shots=100, seed=42)\n",
    "print(f\"SWAP |10> = {result.counts}\")\n",
    "\n",
    "# iSWAP: SWAP with a phase\n",
    "circuit = qs.Circuit(2).x(0).iswap(0, 1).measure_all()\n",
    "result = qs.run(circuit, shots=100, seed=42)\n",
    "print(f\"iSWAP |10> = {result.counts}\")\n",
    "\n",
    "# DCX (Double-CX)\n",
    "circuit = qs.Circuit(2).x(0).dcx(0, 1).measure_all()\n",
    "result = qs.run(circuit, shots=100, seed=42)\n",
    "print(f\"DCX |10> = {result.counts}\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d2ce118a",
   "metadata": {},
   "source": [
    "## Three-Qubit Gates"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b7156555",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Toffoli (CCX): AND gate — flips target only when both controls are |1>\n",
    "for input_state in ['000', '010', '100', '110']:\n",
    "    circuit = qs.Circuit(3)\n",
    "    if input_state[0] == '1': circuit.x(0)\n",
    "    if input_state[1] == '1': circuit.x(1)\n",
    "    circuit.ccx(0, 1, 2).measure_all()\n",
    "    result = qs.run(circuit, shots=100, seed=42)\n",
    "    print(f\"Toffoli |{input_state}> = {result.most_likely}\")\n",
    "\n",
    "print(\"\\nToffoli acts as AND gate on the target qubit!\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "9275b84b",
   "metadata": {},
   "outputs": [],
   "source": [
    "# Fredkin (CSWAP): Controlled-SWAP\n",
    "# Swaps qubits 1,2 only when control (qubit 0) is |1>\n",
    "circuit = qs.Circuit(3).x(0).x(1).cswap(0, 1, 2).measure_all()\n",
    "result = qs.run(circuit, shots=100, seed=42)\n",
    "print(f\"Fredkin |110> = {result.most_likely} (swapped q1,q2)\")\n",
    "\n",
    "circuit = qs.Circuit(3).x(1).cswap(0, 1, 2).measure_all()\n",
    "result = qs.run(circuit, shots=100, seed=42)\n",
    "print(f\"Fredkin |010> = {result.most_likely} (control=0, no swap)\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "05eeced7",
   "metadata": {},
   "outputs": [],
   "source": [
    "# CCZ: Controlled-CZ\n",
    "# Applies phase -1 only to |111>\n",
    "circuit = qs.Circuit(3)\n",
    "circuit.h(0).h(1).h(2)  # Superposition\n",
    "circuit.ccz(0, 1, 2)    # Phase flip |111>\n",
    "circuit.h(0).h(1).h(2)  # Interfere\n",
    "circuit.measure_all()\n",
    "result = qs.run(circuit, shots=2000, seed=42)\n",
    "print(f\"H-CCZ-H on |+++>: {result.counts}\")"
   ]
  }
 ],
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