Individual control of barium ion qubits for quantum information processing
Akbar Jahangiri Jozani, Xinghe Tan, Akimasa Ihara, Ali Khatai, Collin J. C. Epstein, Anastasiia Bershanska, Mahmoud Badawy, Crystal Senko, Rajibul Islam
We present our progress in developing a programmable quantum processor with up to 16 barium ion qubits. Our system utilizes barium's visible-wavelength transitions and long-lived quantum states. We use a Sandia-fabricated surface ion trap with 94 DC electrodes for precise confining potential control. Our hardware innovations include specialized methods for radioactive source preparation and a centrally mounted trap that enables high optical access from multiple directions while maintaining optimized vacuum pressure for long ion lifetime. We implement novel waveguide technology for controlling laser parameters at each ion with negligible crosstalk. As part of the Open Quantum Design initiative, this system will provide remote access for researchers.
We present our progress in developing a programmable quantum processor with up to 16 barium ion qubits. Our system utilizes barium's visible-wavelength transitions and long-lived quantum states. We use a Sandia-fabricated surface ion trap with 94 DC electrodes for precise confining potential control. Our hardware innovations include specialized methods for radioactive source preparation and a centrally mounted trap that enables high optical access from multiple directions while maintaining optimized vacuum pressure for long ion lifetime. We implement novel waveguide technology for controlling laser parameters at each ion with negligible crosstalk. As part of the Open Quantum Design initiative, this system will provide remote access for researchers.
Monolithic integration of control technologies for atomic systems presents a promising route to the development of quantum computers and portable quantum sensors. Trapped atomic ions form the basis of high-fidelity quantum information processors and high-accuracy optical clocks, but currently rely on free-space optics for ion control, limiting portability and scalability. Here we demonstrate a surface-electrode ion trap which delivers all wavelengths required for ionization, cooling, coherent operations, and quantum-state preparation and detection of Sr+ qubits using integrated waveguides and grating couplers. Laser light from the violet to the infrared is coupled onto the chip via an optical-fiber array, creating an inherently stable optical path that we use to demonstrate qubit coherence resilient to platform vibrations. This demonstration of CMOS-compatible integrated-photonic surface-trap fabrication, robust packaging, and enhanced qubit coherence represents a key advance in the development of portable trapped-ion quantum sensors and clocks, and it lights the way toward the complete, individual control of larger numbers of ions in quantum information processing systems.
Abstract Monolithic integration of control technologies for atomic systems is a promising route to the development of quantum computers and portable quantum sensors1–4. Trapped atomic ions form the basis of high-fidelity quantum information processors5, 6 and high-accuracy optical clocks7. However, current implementations rely on free-space optics for ion control, which limits their portability and scalability. Here we demonstrate a surface-electrode ion-trap chip8, 9 using integrated waveguides and grating couplers, which delivers all the wavelengths of light required for ionization, cooling, coherent operations and quantum state preparation and detection of Sr+ qubits. Laser light from violet to infrared is coupled onto the chip via an optical-fibre array, creating an inherently stable optical path, which we use to demonstrate qubit coherence that is resilient to platform vibrations. This demonstration of CMOS-compatible integrated photonic surface-trap fabrication, robust packaging and enhanced qubit coherence is a key advance in the development of portable trapped-ion quantum sensors and clocks, providing a way towards the complete, individual control of larger numbers of ions in quantum information processing systems.
Trapped ions provide a high-fidelity platform for quantum information processing, yet delivery of multiple, distinct wavelengths across large networks of interaction zones remains a bottleneck. Conventional free-space light delivery lacks scalability, while on-chip grating couplers suffer from narrow operational bandwidth that increases circuit footprint and optical interfacing complexity. Here we show a broadband photonic integrated circuit capable of addressing individual ions. The circuit combines a planar waveguide lens with a micromirror fabricated using two-photon polymerization at wafer scale. This implementation can address three individual ions from λ = 405 - 880 nm with -27 dB average intensity crosstalk at 5μm pitch. We trap 40Ca+ and 138Ba+ ions above such devices, characterize optical crosstalk with barium ions, and demonstrate individual repumping of calcium ions. This monolithic photonic architecture brings broadband addressing in an on-chip modality to trapped-ion technology. More generally, integrating additive manufacturing into quantum devices is poised to unlock expanded design space for implementing novel quantum architectures.
Abstract Practical and useful quantum information processing requires substantial improvements with respect to current systems, both in the error rates of basic operations and in scale. The fundamental qualities of individual trapped-ion1 qubits are promising for long-term systems2, but the optics involved in their precise control are a barrier to scaling3. Planar-fabricated optics integrated within ion-trap devices can make such systems simultaneously more robust and parallelizable, as suggested by previous work with single ions4. Here we use scalable optics co-fabricated with a surface-electrode ion trap to achieve high-fidelity multi-ion quantum logic gates, which are often the limiting elements in building up the precise, large-scale entanglement that is essential to quantum computation. Light is efficiently delivered to a trap chip in a cryogenic environment via direct fibre coupling on multiple channels, eliminating the need for beam alignment into vacuum systems and cryostats and lending robustness to vibrations and beam-pointing drifts. This allows us to perform ground-state laser cooling of ion motion and to implement gates generating two-ion entangled states with fidelities greater than 99.3(2) per cent. This work demonstrates hardware that reduces noise and drifts in sensitive quantum logic, and simultaneously offers a route to practical parallelization for high-fidelity quantum processors5. Similar devices may also find applications in atom- and ion-based quantum sensing and timekeeping6.
This thesis focuses on the design of a vacuum system for a trapped ion quantum computer that will house an advanced ion chip trap from Sandia National Laboratories, capable of performing high fidelity operations on up to tens of qubits. The thesis will outline the different design considerations, criteria, and serve to document the final design choices, in addition to optical design work that will be used to drive resonant atomic transitions in the qubit of choice, 133Ba+, as well as the qudit, 137Ba+.
Trapped-ion quantum information processing may benefit from qubits encoded in isotopes that are practically available in only small quantities, e.g., due to low natural abundance or radioactivity. Laser ablation provides a method of controllably liberating neutral atoms or ions from low-volume targets, but energetic ablation products can be difficult to confine in the small ion-electrode distance, micron-scale microfabricated traps amenable to high-speed, high-fidelity manipulation of ion arrays. Here, we investigate ablation-based ion loading into surface-electrode traps of different sizes to test a model describing ion loading probability as a function of effective trap volume and other trap parameters. We characterize loading of ablated barium from a metallic source in two cryogenic surface-electrode traps with 730 and 50 μm ion-electrode distances. Our loading rate agrees with a predictive analytical model, providing insight for the confinement of limited-quantity species of interest for quantum computing, simulation, and sensing.