Dense arrays of trapped ions provide one way of scaling up ion trap quantum information processing. However, miniaturization of ion traps is currently limited by sharply increasing motional state decoherence at sub-100 µm ion-electrode distances. We characterize heating rates in cryogenically cooled surface-electrode traps, with characteristic sizes in 75 µm to 150 µm range. Upon cooling to 6 K, the measured rates are suppressed by 7 orders of magnitude, two orders of magnitude below previously published data of similarly sized traps operated at room temperature. The observed noise depends strongly on fabrication process, which suggests further improvements are possible.PACS numbers: 32.80. Pj, 39.10.+j, 42.50.Vk Quantum information processing offers a tantalizing possibility of a significant speedup in execution of certain algorithms [1,2], as well as enabling previously unmanageable simulations of large quantum systems [3,4]. One of the most promising avenues towards practical quantum computation uses trapped ions as qubits. Interaction between qubits can be mediated by superconductive wires [5], photons [6,7] or by shared phonon modes [8]. The last scheme has been most successful so far, having demonstrated one and two qubit gates [9], teleportation [10,11], error correction[12] and shuttling [13]. Scaling of these experiments to a large number of ions will require arrays of small traps, on the order of 10 µm, to achieve dense qubit packing, improve the gate speed and reduce the time necessary to shuttle ions between different traps in the array [14,15,16,17]. Micro-fabrication techniques have been successfully used to fabricate a new generation of ion traps, demonstrating trap sizes down to 30 µm [18,19,20]. However, as the trap size is decreased, ion heating and decoherence of the motional quantum state increases rapidly, approximately as the fourth power of the trap size [21,22,23]. At currently observed values, the heating rate in a 10 µm trap would exceed 10 6 quanta/s, precluding ground-state cooling or qubit operations mediated by the motional state.The strong distance dependence of the heating rate suggests that the electric field noise is generated by surface charge fluctuations, which are small compared to the distance to the ion. Charge noise is also observed in condensed matter systems, where device fabrication has proven critical in reducing the problem [24,25]. Similar advances in ion traps are impeded by lack of data and models accurately predicting measured noise [26,27,28]. The charge fluctuations have been demonstrated to be thermally driven, providing another plausible route to reduce the heating. Cooling of the electrodes to 150 K has been shown to significantly decrease the heating rate [23].In this Letter, we present the first measurements of heating rates in ion traps cooled to 6 K. We designed and built a range of surface-electrode traps, in which we are able to cool a single ion to motional ground state with high fidelity and observe heating on a quantum level. Although the traps h...

We describe an optical atomic clock based on quantum-logic spectroscopy of the 1 S0 ↔ 3 P0 transition in 27 Al + with a systematic uncertainty of 9.4 × 10 −19 and a frequency stability of 1.2 × 10 −15 / √ τ. A 25 Mg + ion is simultaneously trapped with the 27 Al + ion and used for sympathetic cooling and state readout. Improvements in a new trap have led to reduced secular motion heating, compared to previous 27 Al + clocks, enabling clock operation with ion secular motion near the three-dimensional ground state. Operating the clock with a lower trap drive frequency has reduced excess micromotion compared to previous 27 Al + clocks. Both of these improvements have led to a reduced time-dilation shift uncertainty. Other systematic uncertainties including those due to blackbody radiation and the second-order Zeeman effect have also been reduced.

Laser cooling and trapping of atoms and atomic ions has led to numerous advances including the observation of exotic phases of matter [1,2], development of exquisite sensors [3] and state-of-the-art atomic clocks [4]. The same level of control in molecules could also lead to profound developments such as controlled chemical reactions and sensitive probes of fundamental theories [5], but the vibrational and rotational degrees of freedom in molecules pose a formidable challenge for controlling their quantum mechanical states. Here, we use quantumlogic spectroscopy (QLS) [6] for preparation and nondestructive detection of quantum mechanical states in molecular ions [7]. We develop a general technique to enable optical pumping and preparation of the molecule into a pure initial state. This allows for the observation of high-resolution spectra in a single ion (here CaH + ) and coherent phenomena such as Rabi flopping and Ramsey fringes. The protocol requires a single, far-off resonant laser, which is not specific to the molecule, so that many other molecular ions, including polyatomic species, could be treated with the same methods in the same apparatus by changing the molecular source. Combined with long interrogation times afforded by ion traps, a broad range of molecular ions could be studied with unprecedented control and precision, representing a critical step towards proposed applications, such as precision molecular spectroscopy, stringent tests of fundamental physics, quantum computing, and precision control of molecular dynamics [8].Significant progress has been made in recent years toward the goals of controlling the quantum mechanical states of ultracold molecules [9,10] (also see Methods). For a molecular ion, its charge provides a means of trapping and sympathetically cooling via its Coulomb interaction with a co-trapped atomic ion that is readily laser-cooled [11]. Cooling of vibrational [12] and rotational [13][14][15][16] states has also been realized in heteronuclear molecular ions. Preparation in specific vibrational and rotational states was achieved via threshold photoionization [17] and optical pumping into individual hyperfine states has been demonstrated [18]. In the context of QLS, state detection of a single molecular ion in a particular subset of states in a rotational manifold has been achieved [7]. Many of these experiments rely on fortuitous molecular properties [9,13], dedicated multi-laser systems [9,14,15,18] or sophisticated laser cooling techniques [10]. Coherent control of pure quantum states of a molecular ion, crucial to precision experiments, has not yet been accomplished. 2Here, we demonstrate a general protocol for coherent manipulation of trapped molecular ions in their electronic and vibrational ground states based on QLS [6] and stimulated Raman transitions (SRTs) driven by a far-detuned laser source [19][20][21]. Because the rotational motion is not cooled, our approach relies on probabilistically preparing a particular rotational state via a projective measurement [22]. We...