Any quantum system, such as those used in quantum information or magnetic resonance, is subject to random phase errors that can dramatically affect the fidelity of a desired quantum operation or measurement. In the context of quantum information, quantum error correction techniques have been developed to correct these errors, but resource requirements are extraordinary. The realization of a physically tractable quantum information system will therefore be facilitated if qubit (quantum bit) error rates are far below the so-called fault-tolerance error threshold, predicted to be of the order of 10(-3)-10(-6). The need to realize such low error rates motivates a search for alternative strategies to suppress dephasing in quantum systems. Here we experimentally demonstrate massive suppression of qubit error rates by the application of optimized dynamical decoupling pulse sequences, using a model quantum system capable of simulating a variety of qubit technologies. We demonstrate an analytically derived pulse sequence, UDD, and find novel sequences through active, real-time experimental feedback. The latter sequences are tailored to maximize error suppression without the need for a priori knowledge of the ambient noise environment, and are capable of suppressing errors by orders of magnitude compared to other existing sequences (including the benchmark multi-pulse spin echo). Our work includes the extension of a treatment to predict qubit decoherence under realistic conditions, yielding strong agreement between experimental data and theory for arbitrary pulse sequences incorporating nonidealized control pulses. These results demonstrate the robustness of qubit memory error suppression through dynamical decoupling techniques across a variety of qubit technologies.

We report reliable transport of (9)Be(+) ions through an "X junction" in a 2D trap array that includes a separate loading and reservoir zone. During transport the ion's kinetic energy in its local well increases by only a few motional quanta and internal-state coherences are preserved. We also examine two sources of energy gain during transport: a particular radio-frequency noise heating mechanism and digital sampling noise. Such studies are important to achieve scaling in a trapped-ion quantum information processor.

We report on the design, fabrication, and preliminary testing of a 150 zone array built in a 'surface-electrode' geometry microfabricated on a single substrate. We demonstrate transport of atomic ions between legs of a 'Y'-type junction and measure the in-situ heating rates for the ions. The trap design demonstrates use of a basic component design library that can be quickly assembled to form structures optimized for a particular experiment.

We present a detailed experimental study of the Uhrig Dynamical Decoupling (UDD) sequence in a variety of noise environments. Our qubit system consists of a crystalline array of 9 Be + ions confined in a Penning trap. We use an electron-spin-flip transition as our qubit manifold and drive qubit rotations using a 124 GHz microwave system. We study the effect of the UDD sequence in mitigating phase errors and compare against the well known CPMG-style multipulse spin echo as a function of pulse number, rotation axis, noise spectrum, and noise strength. Our results agree well with theoretical predictions for qubit decoherence in the presence of classical phase noise, accounting for the effect of finite-duration π pulses. Finally, we demonstrate that the Uhrig sequence is more robust against systematic over/underrotation and detuning errors than is multipulse spin echo, despite the precise prescription for pulse-timing in UDD.

The ability to detect extremely small forces and nanoscale displacements is vital for disciplines such as precision spin-resonance imaging [1], microscopy [2], and tests of fundamental physical phenomena [3][4][5]. Current force-detection sensitivity limits have surpassed 1 aN/ √ Hz [6,7] (atto = 10 −18 ) through coupling of nanomechanical resonators to a variety of physical readout systems [1,[7][8][9][10]]. Here we demonstrate that crystals of trapped atomic ions [11,12] behave as nanoscale mechanical oscillators and may form the core of exquisitely sensitive force and displacement detectors. We report the detection of forces with a sensitivity 390±150 yN/ √ Hz (more than three orders of magnitude better than existing reports using nanofabricated devices [7]), and discriminate ion displacements ∼18 nm. Our technique is based on the excitation of tunable normal motional modes in an ion trap [13] and detection via phase-coherent Doppler velocimetry [14,15], and should ultimately permit force detection with sensitivity better than 1 yN/ √ Hz [16]. Trappedion-based sensors could permit scientists to explore new regimes in materials science where augmented force, field, and displacement sensitivity may be traded against reduced spatial resolution. Trapped atomic ions exhibit well characterized and broadly tunable (kHz to MHz) normal motional modes in their confining potential [16,17]. The presence of these modes, the light mass of atomic ions, and the strong coupling of charged particles to external fields makes trapped ions excellent detectors of small forces with tunable spectral response [13]. Another advantage is that readout is achieved through resonant-fluorescence detection using only a single laser. Previous studies have suggested that by using ions it is possible to measure forces approaching the yoctonewton scale, for instance, through experiments on motional heating in Paul traps due to fluctuating electric fields [18][19][20], or resonant excitation techniques [17,21].In particular, small forces applied to ions in weak trapping potentials (trapping frequencies ∼0.1 MHz or lower) can excite micron-scale motional excursions resolvable using real-space imaging [21,22].While the intrinsic sensitivity of trapped ions to external forces and fields is well supported, it remains an experimental challenge to determine the maximum achievable sensitivity to a given external excitation as set by systematic limitations including the efficiency of a measurement procedure. Establishing ions as components in ultrasensitive detectors requires two primary issues to be addressed: a known excitation must be applied to allow precise calibration of the system's response; and it must be possible to compare the results of these experiments with the existing literature on detectors based on integrated nanostructures. Our aims are to unify the seemingly disparate fields of nanotechnology and atomic devices, through use of comparable experimental conditions and a demonstration of the potential utility of ion-based sensors...