Quantum metrology at the Heisenberg limit with ion traps
  Sub-Planck phase-space structures in the Wigner function of the motional degree of freedom of a trapped ion can be used to perform weak force measurements with Heisenberg-limited sensitivity. We propose methods to engineer the Hamiltonian of the trapped ion to generate states with such small scale structures, and we show how to use them in quantum metrology applications. 
D.A.R. Dalvit, R.L. de Matos Filho, and F. Toscano