Craig Robert Clark

Resource requirements for fault-tolerant quantum simulation: The ground state of the transverse Ising model

We estimate the resource requirements, the total number of p hysical qubits and computational time, required to compute the ground state energy of a 1-D qua ntum Transverse Ising Model (TIM) of N spin-1/2 particles, as a function of the system size and the n umerical precision. This estimate is based on analyzing the impact of fault-tolerant quantum e rror correction in the context of the Quantum Logic Array (QLA) architecture. Our results show th at due to the exponential scaling of the computational time with the desired precision of the ene rgy, significant amount of error correciton is required to implement the TIM problem. Comparison of our r esults to the resource requirements for a fault-tolerant implementation of Shor’s quantum fact oring algorithm reveals that the required logical qubit reliability is similar for both the TIM proble m and the factoring problem.

Detection of single-ion spectra by Coulomb-crystal heating

The coupled motion of ions in a radiofrequency trap has been used to connect the frequency-dependent laser-induced heating of a sympathetically cooled spectroscopy ion with changes in the fluorescence of a laser-cooled control ion. This technique, sympathetic heating spectroscopy, is demonstrated using two isotopes of calcium. In the experiment, a few scattered photons from the spectroscopy ion are transformed into a large deviation from the steady-state fluorescence of the control ion. This allows us to detect an optical transition where the number of scattered photons is below our fluorescence detection limit. Possible applications of the technique to molecular ion spectroscopy are briefly discussed.

Identifying single molecular ions by resolved sideband measurements.

The masses of single molecular ions are nondestructively measured by cotrapping the ion of interest with a laser-cooled atomic ion, (40)Ca(+). Measurement of the resolved sidebands of a dipole forbidden transition on the atomic ion reveals the normal-mode frequencies of the two ion system. The mass of two molecular ions, (40)CaH(+) and (40)Ca(16)O(+), are then determined from the normal-mode frequencies. Isotopes of Ca(+) are used to determine the effects of stray electric fields on the normal mode measurement. The future use of resolved sideband experiments for molecular spectroscopy is also discussed.

Assembling a ring-shaped crystal in a microfabricated surface ion trap

We report on experiments with a microfabricated surface trap designed for trapping a chain of ions in a ring. Uniform ion separation over most of the ring is achieved with a rotationally symmetric design and by measuring and suppressing undesired electric fields. After minimizing these fields the ions are confined primarily by an rf trapping pseudo-potential and their mutual Coulomb repulsion. The ring-shaped crystal consists of approximately 400 Ca

Characterization of fluorescence collection optics integrated with a micro-fabricated surface electrode ion trap.

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Laser-cooled atomic ions as probes of molecular ions

ions with an estimated average separation of 9

Surface ion trap structures with excellent optical access for quantum information processing

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Micro-fabricated ion traps for Quantum Information Processing; Highlights and lessons learned.

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Characterization of a High-Optical-Access surface trap optimized for quantum information processing.

One of the outstanding challenges for ion trap quantum information processing is to accurately detect the states of many ions in a scalable fashion. In the particular case of surface traps, geometric constraints make imaging perpendicular to the surface appealing for light collection at multiple locations with minimal cross-talk. In this report we describe an experiment integrating Diffractive Optic Elements (DOEs) with surface electrode traps, connected through in-vacuum multi-mode fibers. The square DOEs reported here were all designed with solid angle collection efficiencies of 3.58%; with all losses included a detection efficiency of 0.388% (1.02% excluding the PMT loss) was measured with a single Ca+ ion. The presence of the DOE had minimal effect on the stability of the ion, both in temporal variation of stray electric fields and in motional heating rates.

Scalable micro-fabricated ion traps for Quantum Information Processing.

Trapped laser-cooled atomic ions are a new tool for understanding cold molecular ions. The atomic ions not only sympathetically cool the molecular ions to millikelvin temperatures, but the bright atomic ion fluorescence can also serve as a detector of both molecular reactions and molecular spectra. We are working towards the detection of single molecular ion spectra by sympathetic heating spectroscopy. Sympathetic heating spectroscopy uses the coupled motion of two trapped ions to measure the spectra of one ion by observing changes in the fluorescence of the other ion. Sympathetic heating spectroscopy is a generalization of quantum logic spectroscopy, but does not require ions in the motional ground state or coherent control of the ion internal states. We have recently demonstrated this technique using two isotopes of Ca+ [Phys. Rev. A, 81, 043428 (2010)]. Limits of the method and potential applications for molecular spectroscopy are discussed.