We’re currently in the fourth generation of computers with the microprocessors after vacuum tubes, transistors and integrated circuits. They were all based on conventional computing.

The fifth generation of computers is currently under development of which quantum computing or quantum computers.

Quantum computers could one day replace silicon chips, just like the transistor once replaced the vacuum tube. But for now, the technology required to develop such a quantum computer is beyond our reach. Most research in quantum computing is still very theoretical.

**Quantum Computer**

Quantum computing is the use of quantum-mechanical phenomena such as superposition and entanglement to perform computation.

A quantum computer is used to perform such computation, which can be implemented theoretically or physically.

Quantum computers are based on the phenomenon of Quantum Mechanics, the phenomenon where it is possible to be in more than one state at a time.

Quantum computing is based on the fact that, in the microscopic world. Tiny particles, such as electrons or photons, can simultaneously take on states that we would normally deem mutually exclusive.

A quantum computer works with particles that can be in superposition. Rather than representing bits – such particles would represent qubits, which can take on the value 0, or 1, or both simultaneously.

A quantum computer, maintains a sequence of qubits, which can represent a one, a zero, or any quantum superposition of those two qubit states; a pair of qubits can be in any quantum superposition of 4 states, and three qubits in any superposition of 8 states.

Qubit– In quantum computing, a qubit or quantum bit (sometimes qbit) is the basic unit of quantum information – the quantum version of the classical binary bit physically realized with a two-state device.

Until now, most silicon-based qubits have been made from the electron or the nucleus of a single phosphorus atom.

**Digital Electronic Computer**

A digital electronic computer is a computer machine which is both an electronic computer and a digital computer.

Examples of a digital electronic computers include the IBM PC, the Apple Macintosh as well as modern smartphones.

Electronic computing which is based on the classical phenomenon of electrical circuits being in a single state at a given time, either on or off.

Ordinary computer works on 0s and 1s. Whatever task you want it to perform, the task is translated into a string of 0s and 1s (the input), which is then processed by an algorithm. A new string of 0s and 1s pops out at the end (the output), which encodes the result.

**Difference between Quantum and Digital Electronic Computer**

Quantum Computer |
Digital Electronic Computer |

A device for computation that makes direct use of distinctively quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. | A computer machine which is both an electronic computer and a digital computer. |

It is large scale integrated multi-purpose computer. | It is high speed parallel computer based on quantum mechanics. |

Quantum computing use Qubits i.e. 0, 1 and superposition state of both 0 and 1 to represent information. | Conventional computing use binary codes i.e. bits 0 or 1 to represent information. |

In quantum computers, data processing is done in Quantum Processing Unit or QPU, which consists of a number of interconnected qubits. | In conventional computers, data processing is done in Central Processing Unit or CPU, which consists of Arithmetic and Logic Unit (ALU), processor registers and a control unit. |

Superconducting Quantum Interference Device or SQUID or Quantum Transistors are the basic building blocks of quantum computers. | CMOS transistors are the basic building blocks of conventional computers. |

Circuit behaviour is governed explicitly by quantum mechanics. | Circuit behaviour is governed by classical physics. |

Information processing is carried out by Quantum logic gates. | Information processing is carried out by logic gates e.g. NOT, AND, OR etc. |

Information storage is Quantum bit based on direction of an electron spin. | Information storage is bit based on voltage or charge etc. |

The Father of Quantum Computing. David Deutsch | The father of the first digital computer was born 110 years ago. John Vincent Atanasoff |

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