S. C. Webster

High-Fidelity Readout of Trapped-Ion Qubits

We demonstrate single-shot qubit readout with a fidelity sufficient for fault-tolerant quantum computation. For an optical qubit stored in 40Ca+ we achieve 99.991(1)% average readout fidelity in 10(6) trials, using time-resolved photon counting. An adaptive measurement technique allows 99.99% fidelity to be reached in 145 micros average detection time. For 43Ca+, we propose and implement an optical pumping scheme to transfer a long-lived hyperfine qubit to the optical qubit, capable of a theoretical fidelity of 99.95% in 10 micros. We achieve 99.87(4)% transfer fidelity and 99.77(3)% net readout fidelity.

Isotope-selective photoionization for calcium ion trapping

We present studies of resonance-enhanced photoionization for isotope-selective loading of

Implementation of a symmetric surface-electrode ion trap with field compensation using a modulated Raman effect

{\mathrm{Ca}}^{+}

Deterministic entanglement and tomography of ion–spin qubits

into a Paul trap. The

A pyramidal magneto-optical trap as a source of slow atoms

{4s}^{2}{}^{1}{S}_{0}\ensuremath{\leftrightarrow}4s4p{}^{1}{P}_{1}

Long-lived mesoscopic entanglement outside the Lamb-Dicke regime.

transition of neutral calcium is driven by a 423 nm laser and the atoms are photoionized by a second laser at 389 nm. Isotope selectivity is achieved by using crossed atomic and laser beams to reduce the Doppler width significantly below the isotope shifts in the 423 nm transition. The loading rate of ions into the trap is studied under a range of experimental parameters for the abundant isotope

Suppression of collisional loss from a magnetic trap

{}^{40}{\mathrm{Ca}}^{+}.

Oxford ion-trap quantum computing project

Using the fluorescence of the atomic beam at 423 nm as a measure of the Ca number density, we estimate a lower limit for the absolute photoionization cross section of 170(60) Mb. We achieve loading and laser cooling of all the naturally occurring isotopes, without the need for enriched sources. Laser heating/cooling is observed to enhance the isotope selectivity. In the case of the rare species

Bose-Einstein condensation in a rotating anisotropic TOP trap

{}^{43}{\mathrm{Ca}}^{+}

Optical Bloch equations with multiply connected states

and