Trapped-ion qubits promise certain fundamental advantages for quantum information processing (QIP), owing to their indistinguishability and relatively high isolation from noisy environments. Though these qualities have allowed demonstrations of the necessary primitives for quantum computation, the complexity of the optical apparatus required is a major impediment to implementation at scales where quantum systems offer a clear advantage over classical computers. Here, we build on previous work with trap-integrated waveguide optics, describing designs and simulations for commercial foundry-fabricated ion trap chips with integrated Si3N4 waveguides and grating couplers to implement multi-qubit operations. We detail a design intended to address and implement quantum logic gates between 5 ions in a single register, and a configuration which utilizes the stable on-chip path lengths of waveguide devices to enact a novel fast entangling two-qubit gate. The devices and approaches presented here could form elements of a scalable architecture for trapped-ion QIP.
Trapped-ion qubits promise certain fundamental advantages for quantum information processing (QIP), owing to their indistinguishability and relatively high isolation from noisy environments. Though these qualities have allowed demonstrations of the necessary primitives for quantum computation, the complexity of the optical apparatus required is a major impediment to implementation at scales where quantum systems offer a clear advantage over classical computers. Here, we build on previous work with trap-integrated waveguide optics, describing designs and simulations for commercial foundry-fabricated ion trap chips with integrated Si3N4 waveguides and grating couplers to implement multi-qubit operations. We detail a design intended to address and implement quantum logic gates between 5 ions in a single register, and a configuration which utilizes the stable on-chip path lengths of waveguide devices to enact a novel fast entangling two-qubit gate. The devices and approaches presented here could form elements of a scalable architecture for trapped-ion QIP.
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.
Trapped-ion qubits have been advantageous in quantum information processing due to their long coherence times and high-fidelity state preparation, logic gate operation, and readout. In recent years, we have fabricated chips with electrodes – for generating the electric field for trapping ions – and photonic waveguides and grating out-couplers – for delivering light to the ions. The integrated photonics can potentially lower the laser power requirement and lead to faster gates; however, there are challenges that need to be overcome for the platform to be beneficial. Here, we demonstrate single and two qubit gates with Sr+ trapped ion qubits, driven by delivering light to the ions both via free space and integrated photonics. We show that robust quantum logic is within reach using the integrated photonic platform, and the approaches we are taking in mitigating current challenges.
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.
Integrated optical control of trapped-ion qubits leveraging dielectric waveguides photonics within planar-fabricated trap devices offers routes to scaling the optical control critical to trapped-ion quantum computing. The ultraviolet to infrared functionality required for many atomic systems, the multiple metal layers for large-scale trap arrays, and the long-term interest in integration of active functionality and integrated electronics motivates development of foundry-based platforms for such systems, to facilitate accessibility to the complex fabrication involved. Aside from scaling, utilization of such technology in trapped-ion quantum systems further stands to alleviate limitations on basic physical operations employed in both quantum computing and metrology, which experiments are starting to demonstrate. I will summarize our recent results using phase-stable standing-wave delivery practically enabled by integrated photonic addressing to enhance ground-state laser cooling, which we experimentally demonstrate using trap devices with integrated Al2O3 and Si3N4 waveguides for UV-NIR addressing fabricated in a commercial foundry. I will also discuss relevance of similar ideas to alleviating power requirements in laser-based entangling gates, and work in progress towards experimental realization, including in a 300 mm-wafer foundry platform for such devices in development.
Trapped-ion quantum computers, leveraging a quantum charge-coupled device (QCCD) architecture, have world-class performance in the field of quantum computing, offering high fidelities and all-to-all connectivity [1]. While systems have advanced over the last decade, much work remains to scale quantum computers to fault-tolerance. Providing scalable light delivery is one key challenge. Current systems utilize engineered bulk- and fiber-optic-based light delivery systems, external to the vacuum chamber, to deliver arrays of beams to ions. However, fundamental optical limitations preclude the use of such systems when scaling beyond thousands of qubits. Integrated photonic-based beam delivery offers a potential solution, with encouraging proof-of-concept demonstrations from the photonics and quantum communities [2]–[5]. Quantinuum and Sandia National Labs have partnered to accelerate the development of integrated photonics for trapped-ion quantum computing applications, working towards photonic components supporting high-fidelity operations. Here, we present development of photonic integrated components designed to deliver laser light toBa+qubits, utilizing a low-loss, high-confinement, trap-integrable PECVD SiN platform. In order to demonstrate two-qubit gates at 532 nm, we developed low loss, tight bend waveguides, efficient edge couplers, and asymmetric multimode interference (MMI) splitters, along with beam-forming grating out-couplers delivering gaussian beams at the ion plane. For quantum state preparation and measurement (SPAM) applications at4 9 3 n m, we demonstrate fabrication-tolerant splitters and low-crosstalk gratings. Measured component performance shows promise for future trap-integrated demonstrations.
Trapped atomic ions are natural candidates for quantum information processing and have the potential to realize or improve quantum computing, sensing, and networking. These applications often require the collection of individual photons emitted from ions into guided optical modes, in some cases for the production of entanglement between separated ions. Proof-of-principle demonstrations of such photon collection from trapped ions have been performed using high-numerical-aperture lenses or cavities and single-mode fibers, but integrated photonic elements in ion-trap structures offer advantages in scalability and manufacturability over traditional optics. In this paper we analyze structures monolithically fabricated with an ion trap for collecting ion-emitted photons, coupling them into waveguides, and manipulating them via interference. We calculate geometric limitations on collection efficiency for this scheme, simulate a single-layer grating that shows performance comparable to demonstrated free-space optics, and discuss practical fabrication and fidelity considerations. Based on this analysis, we conclude that integrated photonics can support scalable systems of trapped ions that can distribute quantum information via photon-mediated entanglement.