David Lucas

Abstract:

We describe single-shot readout of a trapped-ion multiqubit register using space- and time-resolved camera detection. For a single qubit we measure 0.9(3)×10-4 readout error in 400μs exposure time, limited by the qubit's decay lifetime. For a four-qubit register (a "qunybble"), we measure an additional error of only 0.1(1)×10-4 per qubit, despite the presence of 4% optical cross-talk between neighboring qubits. A study of the cross-talk indicates that the method would scale with a negligible loss of fidelity to 10000 qubits at a density of 1 qubit/μm2, with a readout time of 1μs/qubit. © 2010 The American Physical Society.

Abstract:

We describe the fabrication and characterization of a new surface-electrode Paul ion trap designed for experiments in scalable quantum information processing with Ca+. A notable feature is a symmetric electrode pattern which allows rotation of the normal modes of ion motion, yielding efficient Doppler cooling with a single beam parallel to the planar surface. We propose and implement a technique for micromotion compensation in all directions using an infrared repumper laser beam directed into the trap plane. Finally, we employ an alternate repumping scheme that increases ion fluorescence and simplifies heating rate measurements obtained by time-resolved ion fluorescence during Doppler cooling.

Abstract:

We demonstrate sympathetic cooling of a C 43 a+ trapped-ion "memory" qubit by a C 40 a+ "coolant" ion sufficiently near the ground state of motion for fault-tolerant quantum logic, while maintaining coherence of the qubit. This is an essential ingredient in trapped-ion quantum computers. The isotope shifts are sufficient to suppress decoherence and phase shifts of the memory qubit due to the cooling light which illuminates both ions. We measure the qubit coherence during ten cycles of sideband cooling, finding a coherence loss of 3.3% per cooling cycle. The natural limit of the method is O (10-4) infidelity per cooling cycle. © 2009 The American Physical Society.