What is Quantum Computing?
When I say theoretical, I’m not being entirely accurate. Some researches have already built devices that seem to be very primitive quantum computers, but this is still a very wide open and experimental field at this point. Below is a nice simple explanation of what quantum computing is: Where a classical computer obeys the well understood laws of classical physics, a quantum computer is a device that harnesses physical phenomenon unique to quantum mechanics (especially quantum interference) to realize a fundamentally new mode of information processing. In a quantum computer, the fundamental unit of information (called a quantum bit or qubit), is not binary but rather more quaternary in nature. This qubit property arises as a direct consequence of its adherence to the laws of quantum mechanics which differ radically from the laws of classical physics. A qubit can exist not only in a state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding t
ng the Quantum Computer The Turing machine, developed by Alan Turing in the 1930s, is a theoretical device that consists of tape of unlimited length that is divided into little squares. Each square can either hold a symbol (1 or 0) or be left blank. A read-write device reads these symbols and blanks, which gives the machine its instructions to perform a certain program. Does this sound familiar? Well, in a quantum Turing machine, the difference is that the tape exists in a quantum state, as does the read-write head. This means that the symbols on the tape can be either 0 or 1 or a superposition of 0 and 1; in other words the symbols are both 0 and 1 (and all points in between) at the same time. While a normal Turing machine can only perform one calculation at a time, a quantum Turing machine can perform many calculations at once. Image used under the GNU Free Documentation License 1.2 The Bloch sphere is a representation of a qubit, the fundamental building block of quantum computers.
This is the very basic premise, but there is more on the site… The basis of quantum computing A classical computer has a memory made up of bits, where each bit holds either a one or a zero. A quantum computer maintains a sequence of qubits. A single qubit can hold a one, a zero, or, crucially, a superposition of these, allowing for an infinite number of states. A quantum computer operates by manipulating those qubits with (possibly a suite of) quantum logic gates. An example of an implementation of qubits for a quantum computer would be the use of particles with two spin states: “up” and “down” (typically written and ). But in fact any system possessing an observable quantity A which is conserved under time evolution and such that A has at least two discrete and sufficiently spaced consecutive eigenvalues, is a suitable candidate for implementing a qubit. That’s because any such system can be mapped onto an effective spin-1/2. Sources:
Quantum computing is a new method of computing with a hypothetical computer, capable of processing speeds impossible by traditional computers. Though the earliest quantum computers have been built, when practical quantum computing machines hit the market, they will revolutionize an entire industry. However, significant progress must be made before quantum computers have a mainstream use. Quantum computing works by being able to make multiple calculations at one time. Traditional computing works by only making one calculation at a time. While traditional machines do these calculations at an impressive speed, only doing one at a time does limit their capabilities. Quantum computers have no such limitations and can do multiple calculations as fast or faster than traditional computers. Though this may not sound like a major advancement, the ability to make multiple calculations at once can make a big difference in quantum computing. In fact, quantum computers could make today’s supercomput
Quantum computing [Ben82] [Fey82] [Fey86] [Deu92] is a new field in computer science that has been developed with our increased understanding of quantum mechanics. It holds the key to computers that are exponentially faster than conventional computers (for certain problems). A quantum computer is based on the idea of a quantum bit or qubit. In classical computers, a bit has a discrete range and can represent either a zero state or a one state. A qubit can be in a linear superposition of the two states. Hence, when a qubit is measured the result will be zero with a certain probability and one with the complementary probability. A quantum register consists of n qubits. Because of superposition, a phenomenon known as quantum parallelism allows exponentially many computations to take place simultaneously, thus vastly increasing the speed of computation. Quantum interference, the analog of Young’s double-slit experiment that demonstrated constructive and destructive interference phenomena o
