Ground state cooling, quantum state engineering and study of decoherence of ions in Paul traps

Abstract

We investigate single ions of 40 Ca + in Paul traps for quantum information processing. Superpositions of the S 1/2 electronic ground state and the metastable D 5/2 state are used to implement a qubit. Laser light on the S 1/2 ↔ D 5/2 transition is used for the manipulation of the ion's quantum state. We apply sideband cooling to the ion and reach the ground state of vibration with up to 99.9% probability. Starting from this Fock state |n = 0 , we demonstrate coherent quantum state manipulation. A large number of Rabi oscillations and a ms-coherence time is observed. Motional heating is measured to be as low as one vibrational quantum in 190 ms. We also report on ground state cooling of two ions. Quantum information processing with trapped ionsTrapped and laser cooled ions in Paul traps are used for an implementation of quantum information processing. Internal electronic states of individual ions serve to hold the quantum information (qubits) and an excitation of common vibrational modes provides the coupling between qubits, which is necessary for quantum logic operations between qubits, more specifically, for the realization of gate operations between two ions. The Cirac-Zoller proposal [1] requires that initially the ions are cooled to the ground state of motion and that the whole system can be coherently manipulated and controlled. The time scale of decoherence and coupling to the environment is required to be much smaller than the time scale of coherent manipulation.

Quantum computation with trapped ions and atoms

“…Example spectra can be found in Refs. (Schmidt-Kaler et al, 2000;Rohde et al, 2001). Spectral resolution of the sidebands imposes a speed limit on gate operations, which will be discussed in section 2.3.…”

Experiments towards quantum information with trapped Calcium ions

“…In separate experiments we also cooled all motional modes of two ions in our linear trap to the ground state [11]. Cooling only one of the 6 motional modes at a time we achieved at least 95% ground state occupation for all modes.…”

Multiparticle entanglement with quantum logic networks: Application to cold trapped ions

“…First experiments on a single ion and two ions were realized by the NIST group in Boulder [18]. Experiments with more ions were done, for example, by the group in Innsbruck [19].…”