Thursday, June 18

QUANTUM COMPUTING


In 1982, Richard Feynman, a Nobel prize-winning physicist thought up the idea of a 'quantum computer', that uses the effects of quantum physics and quantum mechanics to its advantage. The notation of a quantum computer was primarily of a theoretical interest only, but recent years developments have gain attention of the world’s popular researchers. For example, the development was the invention of an algorithm to factor large numbers on a quantum computer, by Peter Shor (Bell Laboratories). By using Shor’s algorithm, the quantum computer would be able to crack codes much more quickly than any ordinary (or classical) computer could perform. By the way a quantum computer is capable of performing Shor's algorithm that would able to break current cryptography techniques in a fraction of seconds. With the motivation provided by Shor’s algorithm, quantum computing has gathered momentum and great interest in researchers around the world are racing to be the first to create a practical quantum computer.

The word quantum derived from the Latin word quantus which means “how much”. Quantum is a discrete quantity of energy proportional in magnitude to the frequency of the radiation. An analogue discrete amount of other physical quantity, such as momentum or electric charge is known as quantum.

The only comprehensible unit by the computer is a bit (binary digit either 0 or 1) which is the smallest. So bit is the basic unit of the classical computer. One of the most intuitive representation of bit is an open(on) or closed(off) switch of the circuit. In today’s modern computer, this representation remains in transistors, with a high voltage possibly denoting a 1 and low voltage possibly denoting a 0. A two state system (0 to 1) is the building block of classical computational device.

A quantum computer is nothing like a classical computer in design; you can't for instance build one from diodes and transistors. In order to design, a new type of technology is required, a technology that enables ‘quantum bits' to exist as coherent superposition of 0 and 1 state. A quantum bit or simply qu-bit is a unit of quantum information. Qu-bit represents both the state memory and the state of entanglement in a system. Quantum entanglement is experimentally verified property of nature. It happens when the particles such as photon, electron, molecules interacts physically and then become separated. This is known as entanglement.

An example of an implementation of the qu-bit is the quantum dot which is the first step taken by the researchers for building a quantum computer. In this phenomenon a single electron is trapped inside a cage of atoms. When the dot (i.e. the electron) is exposed to a pulse of laser light of certain frequency λ for the time interval T, the electron is raised to an excited state: a second burst of laser light causes the electron to fall back to their ground state. The electron ground state and excited state can be thought of as the 0 and 1 states of the qu-bit and the application of the laser light can be regarded as a controlled NOT method as it knocks the qu-bit from 0 to 1 or from 1 to 0. It would therefore seem that quantum dots are a suitable candidate for designing a quantum computer. By the way, there are number of practical problems that are preventing this from happening:

1. The electron only remains in its excited state for about a microsecond before it falls to the ground state.
2. There is a limit to the number of computational steps.
3. Constructing quantum dots is a very difficult process because they are very small. A quantum dot measures, 10 atoms (1 nanometer) across.

The technology needed to build a computer from these dots doesn't yet exist. In the year 2011, Columbia based company D-Wave Systems demonstrated the world’s first commercially quantum computer D-Wave one operating on 128 qu-bit processor named Rainie. It performs single mathematical method named discrete optimization. By using quantum annealing, it also solves optimization problems. Some researchers found later that this system produce no speedup compared to classical computers.

It is sure that quantum computers replace silicon chip, like transistors that replaced the vacuum tubes. But for now on, the technology requisite to develop a full-fledged quantum computer is beyond the reach. In most research in quantum computing are still theoretical.

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