A Pair of Qubits – Quantum Entanglement
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One major problem that physicists studying quantum computing encounter is that a qubit cannot be copied like a classical bit. It is not possible to copy an unknown quantum state because measuring the state collapses the system. In quantum computing, only the results of a measurement can be copied, as measurement collapses the entire system. The solution to the problem of copying qubits is quantum entanglement.
Quantum entanglement occurs when a pair of particles, such as a photon, interacts physically. One method used to entangle photons is firing a laser beam through a diamond, causes individual photons to become a pair of entangled photons.
Quantum entanglement is when the quantum states of two or more objects, in this case qubits, can be described with reference to one another, regardless of spatial separation. This results in a correlation between the physical properties of the various systems. Imagine a pair of Qubits, A and B, were entangled and sent to opposite ends of the earth. If particle A was measured in the horizontal/vertical basis, and measured horizontal, particle A has collapsed. As soon as A was measured, B will take the state relative (vertical) to A. Although B has not been measured, by measuring A, the result of B is known. The transfer of state between A and B occurs over 10,000 times faster than the speed of light, regardless of distance between A and B. However, this information seems as though it proves that there is something faster than the speed of light. This observation is not true, as proven by Bell's theorem.
Bell's Theorem:
Bell's theorem helped explain the phenonenom between two qubits that are quantum entangled. Bell's theorem stated a reason regardingwhy quantum entanglement did not break the principle of special reletivety.
In 1935, Albert Einstein collabrated with twoother scientiests to try a prove that the current understanding of quantum mechanics. refered to as EPR. They concluded that some 'hidden variables' existed causing some of the uncertainty in quantum mechanics. Hidden variables means that there are some microscopic properties of fundamental particles that we are unable to observe directly by means of testing. The Heisenberg Uncertainty Principle, however, says that the 'hidden variables', are not just non-obervable, they do not exist outside of the context of an observation. The Heisenberg Uncertainty Principle deviates from the traditional observation of reality. EPR provided a proof that stated that either there are Hidden Variables in Quantum Mechanics, or the particle attributes are not real and defined until the particle is observed.
Bell's theorem is based on EPR. Bell's theorem concluded that reality is non-local, explaining how Quantum Mechanics does not disprove the Principle of Special Relativity. Non-local means that objects can influence each other across vast distances with no chain of events or in-between forces. This means that distance as human percieve it is mearly an illusion. The universe exists as a blob that escapes all forms of quantatative measurement. Therefore, quantum entanglement does not defy the Principle of Special Relativity as on the quantum level, the speed of light does not exist; speed is just an illusion.