The word "quantum" (plural: quanta) comes from the Latin "quantus," for "how much." In physics, it is a discrete natural unit or packet of energy, charge, angular momentum or other physical property; interpreted by which a photon is as a single quantum of light and a ‘stable’ atom as a single quantum of matter. Quantum Computing proposes the use of quantum mechanics in computers that will harness the power of these quantum units such as atoms and molecules to perform memory and processing tasks. It was first theorized in Quantum Turing Machine in 1981, by a physicist named Paul Benioff at the Argonne National Laboratory.
A quantum computer would be unlike traditional silicon-based computers that uses binary codes of ones and zeros but instead would be based on qubits (quantum bits) which can exist in “superposition” allowing a computer to store information as both zero and one (and all points in between) at the same time. Qubits work in ‘parallelism’ to act as computer memory and a processor and this parallelism allows a quantum computer to work on a million computations at once, while your desktop PC works on one. A 30-qubit quantum computer would equal the processing power of a conventional computer that could run at 10 teraflops (trillions of floating-point operations per second). Today's typical desktop computers run at speeds measured in gigaflops (billions of floating-point operations per second).
Quantum bits represent atoms, ions, photons or electrons and their respective control devices.
• Ion traps use optical or magnetic fields (or a combination of both) to trap ions.
• Optical traps use light waves to trap and control particles.
• Quantum dots are made of semiconductor material and are used to contain and manipulate electrons.
• Semiconductor impurities contain electrons by using "unwanted" atoms found in semiconductor material.
• Superconducting circuits allow electrons to flow with almost no resistance at very low temperatures.
When electrons, molecules etc. interact physically and are separated, ‘quantum entanglement’ occurs where each resulting member of a pair is indefinite (until measured) in terms of important factors such as position, momentum, spin, polarization, etc. which is described as its state. However, when a measurement is made and it causes one member of such a pair to take on a definite value; this is called bumpping. A pair of qubits can be in any quantum superposition of 4 states, and three qubits in any superposition of 8. A quantum computer operates by manipulating those qubits with a fixed sequence of quantum logic gates. The sequence of gates to be applied is called a quantum algorithm.
Scientists have already built basic quantum computers that can perform certain calculations; but a practical quantum computer is still years away. The trick is to design the circuit (the sequence of gates/ algorithms) to produce the answer to a global question about the function (‘constant’ or ‘balanced’) in an output qubit register that can then be read out or measured definitively. As a read-out, a quantum system is probabilistic and the oracle architecture of algorithms (used to answer questions with a simple yes or no) is very suitable for quantum computers although it can generate energy gap behavior resulting from the magnitute of data measurements in its relation to the compexity of the input size. There exist quantum algorithms, such as Simon's algorithm, which run faster than any possible probabilistic classical algorithm.
The key point, of course, is that one does not end a quantum computation with an arbitrary superposition, but aims for a very special, ‘clever’ state. Therefore, there is a need to construct ‘clever’ superpositions that increase the probability of successfully retrieving the result far more than that of a pure guess. Shor's algorithm evaluates a global property and is an example of both a construction of such ‘clever’ superposition and a retrieval of the solution in polynomial time. Shor's algorithm involves three major steps in this context:
- Creates ‘clever’ entangled state with a set of unitary transformations. The result of the computation—a global property of a function—is now ‘hidden’ in this state.
- Projects it on a subspace of the Hilbert space in order to retrieve this result.
- Perform another set of unitary transformations in order to make the result measurable in the original computational basis.
Developments in Quantum Computing
- In 2005, researchers at the University of Michigan built a semiconductor chip which functioned as an ion trap.
- In 2009, researchers at Yale University created the first rudimentary solid-state quantum processor. The two-qubit superconducting chip was able to run elementary algorithms. Each of the two artificial atoms (or qubits) were made up of a billion aluminum atoms but they acted like a single one that could occupy two different energy states.
- Another team, working at the University of Bristol, also created a silicon-based quantum computing chip, based on quantum optics. The team was able to run Shor's algorithm on the chip.
- A team of scientists from Australia and Japan have finally made a breakthrough in quantum teleportation. They have successfully transferred a complex set of quantum data with full transmission integrity achieved. Also the qubits being destroyed in one place but instantaneously resurrected in another, without affecting their superpositions.
- In 2011, D-Wave Systems announced the first commercial quantum annealer on the market by the name D-Wave One. The company claims this system uses a 128 qubit processor chipset.
- A team of physicists at Rice University have created an "electron superhighway" that would utilize quantum particles with a new method known as "quantum spin Hall topological insulator."
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