The coherence of qubits based on single Ca ions

Abstract

Two-level ionic systems, where quantum information is encoded in long lived states (qubits), are discussed extensively for quantum information processing. We present a collection of measurements which characterize the stability of a qubit based on the S 1/2 -D 5/2 transition of single 40 Ca + ions in a linear Paul trap. We find coherence times of ≃1 ms, discuss the main technical limitations and outline possible improvements.

Analysis of dephasing mechanisms in a standing-wave dipole trap

“…Candidates for irreversible dephasing mechanisms include intensity fluctuations (1) and pointing instability of the dipole trap laser (2), heating of the atoms (3), fluctuating magnetic fields (4), fluctuations of the microwave power and pulse duration (5) and spin relaxation due to spontaneous Raman scattering from the dipole trap laser (6 (1) Intensity fluctuations of the trapping laser. The intensity fluctuations are measured by shining the laser onto a photodiode and recording the resulting voltage as a function of time.…”

“…This dephasing of quantum states of trapped particles has recently been studied both with ions [6] and neutral atoms in optical traps [7,8]. In this work, we have analyzed measurements of the dephasing mechanisms acting on the hyperfine ground states of cesium atoms in a standing wave dipole trap.…”

Dynamics of axialized laser-cooled ions in a Penning trap

“…These parameters will also affect N . The other free parameters in Equation (20) are easily controlled by changing the axialization-drive amplitude and detuning.…”

“…This is a variant on a technique previously used in conjunction with buffer-gas cooling in a Penning trap [19]. Although the hyperfine structure of 25 Mg + could, in principle, be used for the storage of quantum information, the ground state and the metastable D 5/2 level of 40 Ca + have already been shown to be a viable system for this purpose [20]. For this reason, and because of the availability of an all-solid-state laser system for addressing the cooling and qubit transitions, we have chosen to investigate the laser cooling of 40 Ca + ions.…”

Generation of pure ionic entangled states via linear optics

“…we use the S 1/2 as stable ground state, S 1 , S 2 as two degenerate metastable state and P 3/2 as excited state. Arbitrary superposition state of this two degenerate metastable states can be prepared by applying a laser pulse of appropriate length, and this process can be realized in a few microsecond [32]. The 40 Ca + in state S 1 or S 2 can be excited into the excited state P 3/2 by applying one σ − or σ + light at 854nm.…”