Quantum Computers :: quantum physics computer

Missing figures With today's technology we are able to squeeze millions of micron wide logic gates and wires onto the surface of silicon chips. It is only a matter of time until we come to a point at which the gates themselves will be made up of a mere handful of atoms. At this scale, matter obeys the rules of quantum mechanics. If computers are to become smaller and more powerful in the future, quantum technology must replace or reinforce what we have today. Quantum computers aren't limited by the binary nature of the classical physical world. Instead, they depend upon observing the state of qubits (quantum bits) that may represent a one or a zero, a combination of the two, or that the state of the qubit is somewhere between 1 and 0. This "blending" of states is known as superposition. "Here a light source emits a photon along a path towards a half-silvered mirror. This mirror splits the light, reflecting half vertically toward detector A and transmiting [sic] half toward detector B. A photon, however, is a single quantized packet of light and cannot be split, so it is detected with equal probability at either A or B. Intuition would say that the photon randomly leaves the mirror in either the vertical or horizontal direction. However, quantum mechanics predicts that the photon actually travels both paths simultaneously! ... This effect, known as single-particle interference, can be better illustrated in a slightly more elaborate experiment, outlined in figure b below:"1 "In this experiment, the photon first encounters a half-silvered mirror, then a fully silvered mirror, and finally another half-silvered mirror before reaching a detector, where each half-silvered mirror introduces the probability of the photon traveling down one path or the other. Once a photon strikes the mirror along either of the two paths after the first beam splitter, the arrangement is identical to that in figure a, and so one might hypothesize that the photon will reach either detector A or detector B with equal probability. However, experiment shows that in reality this arrangement causes detector A to register 100% of the time, and never at detector B!"2 "This is known as quantum interference and results from the superposition of the possible photon states, or potential paths. So although only a single photon is emitted, it appears as though an identical photon exists and travels the 'path not taken,' only detectable by the interference it causes with the original photon when their paths come together again.