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Caption: A) For a normal bit, only two values are possible: zero or one. Quantum bits allow superpositions of one and zero which can be identified with points on the surface of an imaginary Bloch sphere. A quantum computer needs to be able to rotate the qubit in any direction on the sphere. Several experimentally measured rotations on this sphere are shown, demonstrating control of one qubit. B) Normally, the qubit is protected by keeping the charge distribution of the one and zero states indistinguishable. During the exchange operation, It is arranged for the charge distributions for 0 (blue) and 1 (red) to be slightly different, allowing nearby devices to interact. C) A scanning electron microscope image of the device used in this work. Cartoon electrons were added on top (labeled LL, LR, RL, RR) to show where the electrons sit. The different metal gates (in grey) allowed the use of voltages to trap and control pairs of electrons. This image relates to a paper that appeared in the April 13, 2012, issue of Science, published by AAAS. The paper, by M.D. Shulman at Harvard University in Cambridge, MA, and colleagues was titled, “Demonstration of Entanglement of Electrostatically Coupled Singlet-Triplet Qubits.”
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