Two-dimensional arrays of ions can be used as probes of fundamental physics and tools to investigate collective quantum phenomena due to their quantized internal and motional energies that can be coupled between particles. However, most two-dimensional ion arrays form around a single minimum of a smooth potential. This configuration makes individual control of motional interactions between ions challenging, because changes to the curvature of a shared potential well are experienced by all ions in the trap. In this work, I present a different architecture for creating such arrays of trapped ions: the two-dimensional ion microtrap array. These microfabricated, chip-based devices instead create several potential energy minima that can be individually controlled through the application of local potentials, which may be altered dynamically over the course of a single experiment. The ion microtrap array used in this work confines three beryllium-9 ions on the corners of an equilateral triangle that has side lengths of 30 µm. I will discuss the performance of this device, including ion heating rates, and then present the results of experiments that demonstrate predictable quantum control of the ions we trap. The first experiment demonstrates our ability to precisely manipulate the positions of the ions to achieve individual addressing with light beams. In the second experiment, we couple a single quantum of motional energy (a phonon) to multiple ions in the trap to create and manipulate entangled states of quantum motion. The third experiment dynamically tunes the system to directly observe a topological Berry phase using a single phonon. These results show this two-dimensional ion microtrap array is a fully tunable system that can be used to study static and time-dependent interactions and also create, manipulate, and entangle harmonic oscillators while maintaining coherence and conserving energy for a single excitation.
Two-dimensional arrays of ions can be used as probes of fundamental physics and tools to investigate collective quantum phenomena due to their quantized internal and motional energies that can be coupled between particles. However, most two-dimensional ion arrays form around a single minimum of a smooth potential. This configuration makes individual control of motional interactions between ions challenging, because changes to the curvature of a shared potential well are experienced by all ions in the trap. In this work, I present a different architecture for creating such arrays of trapped ions: the two-dimensional ion microtrap array. These microfabricated, chip-based devices instead create several potential energy minima that can be individually controlled through the application of local potentials, which may be altered dynamically over the course of a single experiment. The ion microtrap array used in this work confines three beryllium-9 ions on the corners of an equilateral triangle that has side lengths of 30 µm. I will discuss the performance of this device, including ion heating rates, and then present the results of experiments that demonstrate predictable quantum control of the ions we trap. The first experiment demonstrates our ability to precisely manipulate the positions of the ions to achieve individual addressing with light beams. In the second experiment, we couple a single quantum of motional energy (a phonon) to multiple ions in the trap to create and manipulate entangled states of quantum motion. The third experiment dynamically tunes the system to directly observe a topological Berry phase using a single phonon. These results show this two-dimensional ion microtrap array is a fully tunable system that can be used to study static and time-dependent interactions and also create, manipulate, and entangle harmonic oscillators while maintaining coherence and conserving energy for a single excitation.
Controlled quantum mechanical motion of trapped atomic ions can be used to simulate and explore collective quantum phenomena and to process quantum information. Groups of cold atomic ions in an externally applied trapping potential self-organize into "Coulomb crystals" due to their mutual electrostatic repulsion. The motion of the ions in these crystals is strongly coupled, and the eigenmodes of motion all involve multiple ions. While this enables studies of many-body physics, it limits the flexibility and tunability of the system as a quantum platform. Here, we demonstrate an array of trapped ions in individual trapping sites whose motional modes can be controllably coupled and decoupled by tuning the local applied confining potential for each ion. We show that a single motional quantum, or phonon, can be coherently shared among two or three ions confined at the vertices of an equilateral triangle 30 μm on a side. We can adiabatically tune the ion participation in the motional modes around a closed contour in configuration space, observing that the single-phonon wavefunction acquires a topological Berry phase if the contour encircles a conical intersection of motional eigenvalue surfaces. We observe this phase by single-phonon interference and study its breakdown as the motional mode tuning becomes non-adiabiatic. Our results show that precise, individual quantum control of ion motion in a two-dimensional array can provide unique access to quantum multi-body effects.
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.
A precisely controlled quantum system may reveal a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analogue quantum simulator that makes relevant observables, interactions and states of a quantum model accessible could permit insight into complex dynamics. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here, we operate two-dimensional arrays of three trapped ions in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 μm. In our approach, which is scalable to arbitrary two-dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as a tuning of couplings between ions within experimental sequences. Our work paves the way towards a quantum simulator of two-dimensional systems designed at will.
Microfabricated ion trap chips are at the core of some of the most advanced quantum computers. How a large number of ions is arranged and controlled on an ion trap chip depends on the chosen trap architecture. One such architecture is the quantum spring array (QSA). In the QSA architecture, ion chains are arranged in a two-dimensional lattice and interact with ion chains in neighboring sites in the radial and axial directions of the respective chain. This interaction, or coupling, is mediated by the Coulomb force while keeping ions in separate trapping sites, and scales inversely with the third power of the separation. The capability to control the distance between ions in the lattice is thus essential. In previous works, the radial separation between ions was tuned by controlling the rf pseudo-potential, which revealed to be experimentally challenging to realize while maintaining low heating rates. In this work, we present an ion trap chip design that allows tuning of the radial distance between ions using only dc voltages. The radial transport is executed between different interaction zones, designated for quantum operations, through specifically designed transition zones. A prototype of this type of ion trap chip was microfabricated on fused silica substrate. Its functionality is characterized by demonstrating dc-controlled radial transport of a single ion through a transition zone and measuring stray fields and ion heating rates in the center of the trap. Moreover, the fabrication of a multi-metal layer version of such a trap is presented as a scaling path for the presented chip design.
A custom-built and precisely controlled quantum system may offer access to a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analog quantum simulator that makes the relevant observables, interactions, and states of a quantum model accessible could permit experimental insight into complex quantum dynamics that are intractable on conventional computers. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here we characterise two-dimensional arrays of three ions trapped by radio-frequency fields in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 micrometer. In our approach, which is scalable to arbitrary two dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as tuning of crucial couplings between ions within experimental sequences. Our work paves the way towards an analog quantum simulator of two-dimensional systems designed at will.
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.