Laser addressing of individual ions in a linear ion trap

Abstract

Single ions in a linear string have been addressed with a tightly focused laser beam and an acousto-optic deflector. The excitation into a long-lived metastable level is detected with a quantum jump technique. Singlequantum bit operations for quantum information processing with trapped ions are shown to be feasible.

An efficient single-step scheme for manipulating quantum information of two trapped ions beyond the Lamb–Dicke limit

“…Thus, hereafter we neglect all off-resonant transitions and the excitations of the higher vibrational modes [23,24,25], i.e., let F j =Î, and only label the CM mode excitations. We stress the following important fact: the effective Hamiltonian (3) reduces to that in previous works (e.g., [5,9,12,17] under the usual LD approximation: (m+ 1)η 2 j ≪ 1), to the lowest order of the LD parameter η j . Here m is the occupation number of the Fock state of the CM vibrational quanta.…”

“…Recently, the quantum entanglement of two and four trapped ions have been generated experimentally (see, e.g., [5,10]), although the operations are limited to the weakcoupling LD regime. We now show that the entangled states of two trapped ions can also be produced outside the LD limit.…”

“…The collective normal modes of oscillation shared by all of the ions form the information bus, through which all gate operations can be performed. In the past few years, several key features of the proposal in [6], including the production of entangled states and the implementation of quantum controlled operations between a pair of trapped ions, have already been experimentally demonstrated * lfwei@riken.jp † fnori@riken.jp ‡ Permanent address [5,8,9,10]. Also, several alternative theoretical schemes (see, e.g., [11,12,13,14,15,16,17]) have been developed for overcoming various difficulties in realizing a practical iontrap quantum information processor.…”

“…Intense activities are now focused on generating an entanglement of particles in a deterministic way, i.e., to produce a desired entangled state. For example, the entanglements of two and four trapped ions have been produced experimentally [5].…”

“…The Lamb-Dicke (LD) approximation is made in almost all of these schemes (see, e.g., [5,9,12,16,17]), in order to simplify the treatment of the laser-ion interaction. This approximation requires that the coupling between the external and internal degrees of freedom of the ion is very weak, i.e., the spatial dimension of the motion of the ground state of the trapped ion should be much smaller than the effective wavelength of the applied laser field (see, e.g., [18]).…”