Jonathan P. Home

Combining coherent and dissipative control for quantum state engineering   

ETH Zurich    

I will describe recent experiments in which we have generated a range of Gaussian states of motion of a single trapped ion using reservoir engineering [1]. We make use of multi-frequency laser fields to couple the motional oscillator to a zero temperature reservoir realized through optical pumping of the ion's spin. The engineered spin-motion couplings lead to cooling in a rotated state basis, producing as the ground state the desired state of interest. We use similar couplings to demonstrate novel measurement techniques for oscillator states, providing a direct measure of state fidelity, and also show a sqrt{n} scaling in the engineered basis which is analogous to the Jaynes-Cummings result. These oscillator state measurements have been verified independently first by a Fock state decomposition, and using a second technique involving the use of state-dependent forces to entangle the spin and motion. The latter generates squeezed-wavepacket analogues to the well known Schrodinger's cat states. We observe re-coherence after separating the entangled wavepackets by up to 20 times the ground state r.m.s. extent which corresponds to 63 times the width of the squeezed wavepacket  [2]. I will also briefly describe recent results on Hamiltonian estimation for spin rotations performed by transporting ions through static laser beams.

[1] D. Kienzler et al. Science 347, 6217 (2014)
[2] H-Y. Lo et al., arXiv:1412.7100 (2015)