Current classical computing methods are unable to simulate quantum many-body interactions efficiently.Analog quantum simulators with even small numbers of quantum degrees of freedom are expected to enable the investigation of systems not fully accessible in traditional computing such as condensed-matter systems, quantum chemistry, and material science.Two-dimensional lattices of trapped ions are a good candidate to realize an analog quantum simulator for their addressability, individual control and individual detection.Here, we report on multiple unique lattice surface ion trap designs, microfabricated at Sandia National Laboratories, capable of trapping and interacting up to 4 ions.Ions are held in close proximity in individual all radio-frequency potential minima and interact via their Coulomb repulsion.The Coulomb coupling between ions allows for simulation of spin-spin interactions 1-6 .Control electrodes of the trap can be used to adjust principal axes of the ion's motion and thus enable individual control over the interaction between ions.The lattice trap array architecture tested in this work can be scaled to larger two-dimensional lattices of trapped ions.
Current classical computing methods are unable to simulate quantum many-body interactions efficiently.Analog quantum simulators with even small numbers of quantum degrees of freedom are expected to enable the investigation of systems not fully accessible in traditional computing such as condensed-matter systems, quantum chemistry, and material science.Two-dimensional lattices of trapped ions are a good candidate to realize an analog quantum simulator for their addressability, individual control and individual detection.Here, we report on multiple unique lattice surface ion trap designs, microfabricated at Sandia National Laboratories, capable of trapping and interacting up to 4 ions.Ions are held in close proximity in individual all radio-frequency potential minima and interact via their Coulomb repulsion.The Coulomb coupling between ions allows for simulation of spin-spin interactions 1-6 .Control electrodes of the trap can be used to adjust principal axes of the ion's motion and thus enable individual control over the interaction between ions.The lattice trap array architecture tested in this work can be scaled to larger two-dimensional lattices of trapped ions.
The understanding of quantum mechanical systems is essential to modern physics and its applications. However, already for entangled systems of a few tens of constituents, exact numerical simulations on classical computers can become impossible. Quantum simulators based on well-controlled quantum system might provide the only effective approach to these systems. Trapped atomic ions offer a uniquely precise and controllable platform. They are used as platforms for, e.g., future quantum computers, quantum simulators, and extremely precise clocks. Quantum-simulation problems of interest and out-of-reach for modern theoretical methods include the dynamics of one-dimensional systems on long time scales and more-than-one dimensional systems with long-range interaction. For the latter, two-dimensional arrays of ions, individually trapped and controlled above microfabricated surface-electrode traps, present a promising approach. In the first realizations so far, the inter-site distance between the ions was too large to allow for sufficient inter-site coupling. We aim for a scalable approach to an analog quantum simulator based on a two-dimensional array of individually trapped ions. As a first demonstration, we operate an array of three magnesium ions in triangular arrangement with a side-length of 40µm. Therein, we previously demonstrated the individual control of internal (electronic) and external (motional) degrees of freedom of the ions. Here, we present the first realization of inter-site coupling in the two-dimensional array. We demonstrate the coupling by a transfer of large coherent states of motion between the sites. We investigate the influence of the amplitude of these motional states in the anharmonic trapping potential and extrapolate to future experiments on the single-phonon level. We apply the real-time control of the coupling and concatenate the two-site coupling to transfer motional excitation between all three sites of the array. To demonstrate the scalability of our techniques, we couple all three sites simultaneously and investigate the evolution of an initial excitation at one and two sites of the array. The latter shows interference effects of the different pathways in the triangle. Current motional heating rates on the order of the inter-site coupling, preclude working with single phonons near the motional ground-state. We present a new experimental apparatus and vacuum chamber which will allow in-situ cleaning of surface-electrode traps. This has shown to reduce motional heating rates by two orders of magnitude. In this apparatus, we additionally realize a magnetic-field insensitive qubit in 25Mg+ with a coherence time exceeding six seconds. We generate the magnetic field around 10.9mT by a hybrid magnet assembly based on solid-state magnets and fine-tuned by electric coils. Once we have reduced the heating rate in the triangle trap array using the new setup, first quantum simulation experiments, investigating spin-frustration or artificial gauge fields, will come in reach. Here our triangle represents a basic, scalable, building block of future latices designed at will.
With all the key elements of quantum computing in ion traps demonstrated by the research community, the focus is now placed on building more sophisticated traps with larger numbers of ions to allow practical scale information processing. One promising avenue is to store ions in and shuttle them between many independent traps which serve as potential interaction sites. The core of the work described in this thesis is the experimental evaluation of a microfabricated segmented ion trap, built by Sandia National Laboratories ("Sandia trap"). These experiments required construction of a wholly new optical setup including laser and detection systems, a vacuum system and control electronics. Among our experimental achievements were: successful loading of single and pairs of ions in the microscale trap, measurement of ion storage lifetime, measurement of the motional heating rate with a time-resolved Doppler-cooling method — which showed above than average heating, and implemented a single-ion shuttling method — which reliably transferred the ion through a distance of 360 μm (two DC electrode widths away) and back. These results have been used to improve the next version of the Sandia trap design. We also used computer modelling to study several aspects of ion traps: a mesoscopic ion trap designed for fast ion separation, simulated ion loading to quantify requirements for successful trapping in small and shallow traps, and analyzed a precise shuttling method — where the time dependence of the trapping potential is engineered such that there is minimal motional heating. The results show that ion trap arrays at the 100 μm distance scale are feasible and suggests that such multiple trap designs merit further study.
Trapped ions within Paul traps have shown to be a promising architecture in the realisation of a quantum information processor together with the ability of providing quantum simulations. Linear Paul traps have demonstrated long coherence times with ions being well isolated from the environment, single and multi-qubit gates and the high fidelity detection of states. The scalability to large number of qubits, incorporating all the previous achievements requires an array of linear ion traps. Microfabrication techniques allow for fabrication and micron level accuracy of the trap electrode dimensions through photolithography techniques. The first part of this thesis presents the experiential setup and trapping of Yb+ ions needed to test large ion trap arrays. This include vacuum systems that can host advanced symmetric and asymmetric ion traps with up to 90 static voltage control electrodes. Demonstration of a single trapped Yb+ ion within a two-layer macroscopic ion trap is presented. with an ion-electrode distance of 310(10) µm. The anomalous heating rate and spectral noise density of the trap was measured, a main form of decoherence within ion traps. The second half of this thesis presents the design and fabrication of multi-layer asymmetric ion traps. This allows for isolated electrodes that cannot be accessed via surface pathways, allowing for higher density of electrodes as well as creating novel trap designs that allow for the potential of quantum simulations to be demonstrated. These include two-dimensional lattices and ring trap designs in which the isolated electrodes provide more control in the ion position. For the microfabrication of these traps I present a novel high-aspect ratio electroplated electrode design that provides shielding of the dielectric layer. This provides a means to mitigate stray electric field due to charge build up on the dielectric surfaces. Electrical testing of the trap structures was performed to test bulk breakdown and surface flashover of the ion trap architectures. Results showed sufficient isolation between electrodes for both radio frequency and static breakdown. Surface flashover voltage measurements over the dielectric layer showed an improvement of more than double over previous results using a new fabrication technique. This will allow for more powerful ion trap chips needed for the next generation of microfabricated ion trap arrays for scalable quantum technologies.
Quantum simulations of spin systems could enable the solution of problems that otherwise require infeasible classical resources. Such a simulation may be implemented using a well-controlled system of effective spins, such as a two-dimensional lattice of locally interacting ions. We propose here a layered planar rf trap design that can be used to create arbitrary two-dimensional lattices of ions. The design also leads naturally to ease of microfabrication. As a first experimental demonstration, we confine S88r+ ions in a millimeter-scale lattice trap and verify numerical models of the trap by measuring the motional frequencies. We also confine 440 nm diameter charged microspheres and observe ion-ion repulsion between ions in neighboring lattice sites. Our design, when scaled to smaller ion-ion distances, is appropriate for quantum simulation schemes, e.g., that of Porras and Cirac [Phys. Rev. Lett. 92, 207901 (2004)]. We note, however, that in practical realizations of the trap, an increase in the secular frequency with decreasing ion spacing may make a coupling rate that is large relative to the decoherence rate in such a trap difficult to achieve.
Trapped ions are among the top candidates for realizing high fidelity gate operations for quantum computation as well as other applications including quantum simulation and sensing [1]. However, scaling these systems up to the number of qubits required to solve interesting problems with conventional macroscopic traps quickly becomes intractable. To overcome the scalability challenge, advanced microfabrication techniques have been developed to support a variety of complex electrode layouts, allowing for precise and dynamic control of confining potentials. Using Sandia’s microfabricated surface ion traps, which feature low heating rates, high trap frequencies, and long trapping times, we demonstrate novel classical control techniques that employ parametric voltage solutions for elegant composition of shuttling operations and accurate control over the curvature of the confining potential. To demonstrate the viability of Sandia's microfabricated ion traps for quantum information processing, we’ve realized of high-fidelity single-qubit gates below a rigorous fault tolerance threshold for general noise [2,3] and two-qubit Mølmer-Sørensen gates with a process fidelity of 99.58(6)%.
Trapped ions in Paul traps (radio frequency ion traps) are a promising candidate for the realization of a quantum computer. To date, experimental demonstrations of quantum computing and information processing with trapped ions have been limited to small numbers of quantum bits (qubits). The most prominent challenge to realise ion-trap quantum computation is to scale the system and control a large number of trapped ions coherently. Surface-electrode ion trap designs which are amenable to various microfabrication techniques offer a path to achieve this. In this work, design, fabrication and key operations of two types of surface-electrode ion traps, i.e. a Y-junction trap and a two-dimensional (2D) hexagonal lattice trap developed towards scaling ion-trap architectures, are presented. The steps involved in the fabrication of the ion-trap devices included photolithography, wet etch (hydrofluoric acid etch) and dry etch (deep reactive ion and inductively coupled plasma etching), and metal evaporation. The devices were fabricated on SOI substrates with different buried oxide thicknesses (i.e. 5 µm and 10 µm) and different metals for the trap electrodes (i.e. gold and aluminium). An extremely high-breakdown voltage up to 1 kV was measured in vacuum for the SOI-built test devices with a 10 µm-thick buried oxide formed by oxide film-to-oxide film bonding process. This is attributed to the deep V-shaped undercut profile of the buried oxide layer which resulted in a large breakdown path length, and so mitigating surface breakdown effects. Owing to the V-shaped undercut profile, the surface breakdown voltage was improved by 15% for the devices fabricated on SOI substrates with a 10 µm-thick buried oxide. In the first experiment, the demonstration of ytterbium (174Yb+) ion trapping in the 2D hexagonal lattice trap is achieved with a relatively long lifetime of a laser-cooled ion up to 90 minutes and ≤ 5 minutes without cooling in ultra-high vacuum system. The 2D lattice trap design allows for reliable trapping of 2D ion lattices, rudimentary shuttling between lattice sites and deterministic introducing of defects into the ion lattice. Based on all these abilities, such a 2D lattice trap with the predicted reduction of lattice spacing down to 32 µm can be configured as a versatile architecture for 2D quantum simulations with trapped ions. In the second experiment, microparticle trapping in the 2D lattice trap, performed in air, is achieved with the longest trapping lifetime of 60 minutes. Both gold and aluminium-coated electrodes also lead to comparable trapping performances. Furthermore, the in situ levitation of microparticles is successfully demonstrated at the maximum levitation height of 30 µm. This ability provides additional control on the trapping height which increases the overall functionality of the 2D lattice trap.