Researchers Demonstrate Quantum Walk in Bose-Einstein Condensate

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Researchers from Oklahoma State University manipulated the momenta of ultra-cold atoms to demonstrate a quantum walk

Quantum analogs of a random walk form the basics of proposed search algorithms for quantum computers. These quantum walks are more complex as compared to other conventional counterparts as entanglement and interference among the particles play a major role. Now, a research led by Gil Summy of Oklahoma State University in Stillwater, performed a quantum walk by manipulating the momenta of atoms in a Bose-Einstein condensate.

The ‘walkers’ in previous demonstrations of quantum walks, were atoms or photons moving in real space. The current work is the pioneering demonstration of a walk in momentum space as every step of the walk corresponds to a discrete change in the momentum of walker instead of its position. Moreover, such a momentum-space walk is easier to control than a real-space walk. In the Oklahoma State University experiment, the walkers are ultracold rubidium atoms. A microwave pulse that puts the atoms into a superposition of two hyperfine states initiate a step in the walk. An optical pulse later pushes the atoms to change momentum of each atom. This change in momentum is done by a discrete amount and in a direction that depends on the internal state of the atom. The researchers tracked changes in the overall momentum distribution when the walk proceeded through multiple steps.

Although a Gaussian distribution would be expected for a classical walk, the researchers observed that the momentum distribution evolved to be centered around two peaks. The peaks separate as the walk proceeds, which is a sign of a quantum walk. The team tailored the microwave and optical pulses to show that they can steer and even reverse the walk. This in turn demonstrates a large degree of control that can find applications in both search algorithms and in fundamental tests of quantum mechanics. The research was published in the journal Physical Review Letters on August 16, 2018.

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