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.
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.
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-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.
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 Experiments with trapped ions and neutral atoms typically employ optical modulators in order to control the phase, frequency, and amplitude of light directed to individual atoms. These elements are expensive, bulky, consume substantial power, and often rely on free-space I/O channels, all of which pose scaling challenges. To support many-ion systems like trapped-ion quantum computers or miniaturized deployable devices like clocks and sensors, these elements must ultimately be microfabricated, ideally monolithically with the trap to avoid losses associated with optical coupling between physically separate components. In this work we design, fabricate, and test an optical modulator capable of monolithic integration with a surface-electrode ion trap. These devices consist of piezo-optomechanical photonic integrated circuits configured as multi-stage Mach-Zehnder modulators that are used to control the intensity of light delivered to a single trapped ion on a separate chip. We use quantum tomography employing hundreds of multi-gate sequences to enhance the sensitivity of the fidelity to the types and magnitudes of gate errors relevant to quantum computing and better characterize the performance of the modulators, ultimately measuring single qubit gate fidelities that exceed 99.7%.
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.
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.