Phys. Rev. X 3, 031014 (2013)

The ability to localize atomic excitations on the subwavelength scale could help reduce the required spacing for qubits in quantum information processing and increase the speed of two-qubit gates. Researchers from the University of Wisconsin at Madison in the USA have now managed this feat with a spatial width of 100 nm in a sample of ultracold 87Rb atoms in an optical trap. The team used a laser with a standing-wave pattern to drive electromagnetically induced transparency (EIT) in a sample of atoms. They report that the hyperfine excitation could be localized to a region eight times smaller than the wavelength of the EIT beams. The EIT pulses were 100 ns long, indicating a gate speed capability of about 10 MHz. The team now plans to attempt atomic localization at the 10 nm level by using a different excitation line for the EIT and switching to a longer wavelength for the optical trapping beam in order to cool the atoms to below 1 μK. The ultimate aim is to create single-qubit and two-qubit gates that operate with a subwavelength spatial resolution.