Bell state (IMAGE)
Caption
Conceptual illustration of a Bell state, in which one unit of vibrational energy is shared between two oscillators. The system exists in two possible states simultaneously: the first possible quantum state (in brackets, left of the plus sign) shows the right-hand oscillator vibrating and the left-hand oscillator standing still. The second possible state shows the vibrational energy occupying the left-hand oscillator, with the right-hand one still. The device exists in a superposition of both possible states – meaning that each oscillator is both moving and not moving at the same time – until it is measured. A measurement of the system would yield only one of the two depicted (bracketed) outcomes: If the left-hand oscillator was observed to be vibrating, the right-hand would necessarily be still, and vice versa. This illustrates the entanglement between the two oscillators: By performing a measurement to learn information about the motion of only one oscillator, an observer would also determine the state of the other oscillator, without needing to measure it separately.
Credit
Agnetta Cleland
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License
CC BY-NC-ND