A TRICK of the light is all that鈥檚 needed to create a new kind of quantum logic gate. It is the latest step in the quest for a practical quantum computer, which should in theory vastly outperform any classical computer.
These logic gates are made in an 鈥渙ptical lattice鈥�, an interference pattern created when three laser beams intersect, forming a 3D grid of bright and dark spots. Ultra-cold atoms of rubidium are held by this cage of light, sitting at the dark spots.
Changing the polarisation of the lasers forces pairs of rubidium atoms together, which makes them start to exchange quantum information encoded in the direction of their spins (Nature, ). 鈥淭he spin states are forced to interchange as time progresses,鈥� says team member Benjamin Brown of the Joint Quantum Institute in Gaithersburg, Maryland.
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This leaves the atoms 鈥渆ntangled鈥� in a shared state in which measuring one spin affects the outcome of measurements on the second. Manipulating entanglement is a crucial element of quantum computing. Brown calls the latest experiments 鈥渁 proof of principle, showing you can do the essential operation of a quantum logic gate鈥�.
Quantum gates have been demonstrated using ions, but not with neutral atoms, which have relatively robust quantum states, says Brown. 鈥淚t鈥檚 a very parallel thing we鈥檝e done, with 10,000 or 100,000 pairs of atoms all doing the same quantum dance.鈥�
