The ability to distribute entanglement across a quantum network may lead to new capabilities like teleporting information over a difficult-to-access quantum channel or higher resolution quantum sensors. However, there are many outstanding challenges to realizing such a quantum network. One of these challenges is how to interface disparate quantum technologies effectively and efficiently. Ultimately a quantum network will be used to connect different types of devices, much like the current internet does today, and this requires one to seamlessly connect qubit technologies operating in vastly different environments. This talk will present results on interfacing trapped ion qubits to quantum integrated photonic circuits and discuss challenges related to interfacing trapped ion qubits with superconducting qubits.
The ability to distribute entanglement across a quantum network may lead to new capabilities like teleporting information over a difficult-to-access quantum channel or higher resolution quantum sensors. However, there are many outstanding challenges to realizing such a quantum network. One of these challenges is how to interface disparate quantum technologies effectively and efficiently. Ultimately a quantum network will be used to connect different types of devices, much like the current internet does today, and this requires one to seamlessly connect qubit technologies operating in vastly different environments. This talk will present results on interfacing trapped ion qubits to quantum integrated photonic circuits and discuss challenges related to interfacing trapped ion qubits with superconducting qubits.
Trapped ions are promising candidates for nodes of a scalable quantum network due to their long-lived qubit coherence times and high-fidelity single- and two-qubit gates. Future quantum networks based on trapped ions will require a scalable way to route photons between different nodes. Photonic integrated circuits from fabrication foundries provide a compact solution to this problem. However, these circuits typically operate at telecommunication wavelengths that are incompatible with the strong dipole emissions of trapped ions. In this work, we demonstrate the routing of single photons from a trapped ion using a photonic integrated circuit. We employ quantum frequency conversion to match the emission of the ion to the operating wavelength of a foundry-fabricated silicon nitride photonic integrated circuit, achieving a total transmission of 31.0% \ifmmode\pm\else\textpm\fi{} 0.9% through the device. Using programmable phase shifters, we switch the single photons between the output channels of the circuit and demonstrate a 50:50 beam splitting condition. These results constitute an important step towards programmable routing and entanglement distribution in large-scale quantum networks and distributed quantum computers.
Atomic ions controlled by laser light are among the leading candidates for large scale quantum computing. However operational systems today require vast scaling to reach levels capable of useful computational tasks. The integration of light delivery will be an essential component of this for the trapped-ion approach. I will describe results in which the use of photonics integrated into ion trap chips has allowed us to perform high fidelity two-qubit gates, which are an essential building block for quantum computers. These systems have now been extended to the operation of multiple trap zones, and the creation of novel optical fields for ion trap control while a new generation of chips allowing integration of all required wavelengths as well as optimised light delivery offers further enhancements in performance and scaling.
Trapped ion quantum networking aims at distributing quantum information between distant parties. Entanglement links between distant ions are mediated with photonic qubits, necessitating the need for efficient ion-photon interfaces. This thesis reports on progress towards improving the main limitations of creating a practical quantum network by using diffractive optics for high numerical aperture imaging of trapped ions. The diffractive optics are near-planar, patterned structures which are fabricated to collimate a large fraction of ion uorescence, with low aberration, for high resolution imaging. Patterning the central grounding electrode on a chip trap allows the ion to be within less than 100 microns of the surface. Large scale quantum networks will require a large number of ions and ion-photon interfaces. To scale the ion trap system, microfabricated surface traps can be used allowing for the opportunity to etch diffractive mirrors directly onto the trap surface. Collecting ion uorescence with the diffractive mirror, we show the highest ion-single mode optical fibre coupling efficiency, which enhances the entanglement rate of a quantum network. We then build a high resolution UV spectrometer to distinguish between frequency entangled photonic qubits. Frequency qubits offer more robust encoding when compared with polarisation qubits, as a result of energy conservation. Using the spectrometer we demonstrate correlations between the ion's internal state and the frequency state of an entangled photonic qubit. Quantum networks will require local quantum information processing using ion-ion gates to distribute entanglement over the entire network. Typically, the speed of these gates is presently limited to ~10 µs by the secular trap frequency. We demonstrate the first steps towards a fast ion-ion gate, not limited by the secular frequency, based on strong optical forces generated by the coherent, resonant absorption and stimulated emission of light from an ultrafast, pulsed laser. A full-scale quantum network will require many ion trap installations each with their own laser systems. For this challenge we demonstrate simple, robust, and cost-effective methods to lock the 399 nm photoionisation laser, based on polarisation spectroscopy through a hollow cathode lamp, and an opto-mechanical switch which allows locking of multiple lasers to a wavelength meter. Another scalable diffractive optic used is a phase Fresnel lens integrated into a 3D quadrupole ion trap system. The limits of imaging with this lens are tested by demonstrating force sensing at a sub-attoNewton level with super-resolution imaging techniques to find the ion location.
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 constitute a promising platform for implementation of a quantum network. Recently, a dual-type qubit scheme has been realized in a quantum network node where communication qubits and memory qubits are encoded in different energy levels of the same ion species, such that the generation of ion-photon entanglement on the communication qubits has negligible cross-talk error on the preloaded quantum information in the memory qubits. However, to achieve versatile applications of a quantum network, a crucial component of the dual-type node, namely, the entangling gate between the communication and the memory qubits, is still missing. Here, we report a dual-type quantum network node equipped with ion-photon entanglement generation, cross-talk-free quantum memory, and entangling gates between dual-type qubits simultaneously. We demonstrate its practical applications including the passive quantum-state teleportation and the preparation of multipartite entangled state. Our work achieves the necessary components of a dual-type quantum network node.
Trapped atomic ions are standards for quantum information processing, serving as quantum memories, hosts of quantum gates in quantum computers and simulators, and nodes of quantum communication networks. Quantum bits based on trapped ions enjoy a rare combination of attributes: They have exquisite coherence properties, they can be prepared and measured with nearly 100% efficiency, and they are readily entangled with each other through the Coulomb interaction or remote photonic interconnects. The outstanding challenge is the scaling of trapped ions to hundreds or thousands of qubits and beyond, at which scale quantum processors can outperform their classical counterparts in certain applications. We review the latest progress and prospects in that effort, with the promise of advanced architectures and new technologies, such as microfabricated ion traps and integrated photonics.