Multiwavelength narrow linewidth laser system for Ba+ quantum computing applications

Published in: QUANTUM WEST SPIE 2024

Authors: Kostiantyn Nechay, Luukas Kuusela, Pekko Sipilä, Kalle Palomäki, Petteri Uusimaa

Quantum information processing (QIP) approach based on trapped ions is a promising technology that exploits different ion species as individual qubits and qubit gates, while featuring long coherence times, high fidelity of operations, fast readout, and ion-ion gate entanglement. The practical usefulness of trapped-ion quantum computer depends on its further scaling to a large number of qubits. Meanwhile, trapped-ion quantum computer relies on a set of single-frequency lasers, utilizing them for different functions such as photoionization, atom cooling, optical pumping and qubit operations. Thus, a combination of narrow linewidth lasers is required, with the emission wavelengths precisely defined by the corresponding electronic transitions of the selected ion species. Further development, scalability and commercialization of quantum information technologies is interwind with the availability of affordable and robust single-frequency lasers on a variety of application-specific wavelengths. QIP manifests strict requirements posed to lasers in terms of central wavelength, linewidth, long-term stability, beam quality, polarization extinction ratio, side-mode suppression ratio, etc. In this work we present the development and characterization of multiwavelength narrow linewidth system designed for the Ba+ trapped ion computing. The laser system emits single-frequency, sub-MHz emission at 553 nm, 493 nm and 614 nm based on second-harmonic generation of two separate semiconductor laser platforms. Two-step photoionization of neutral Ba is implemented resonantly through 6s2 1S0 → 6s6p 1P1 transition corresponding to 553 nm wavelength, whereas Ba ion is Doppler cooled on 6S1/2 →6P1/2 transition corresponding to 493 nm. Such single-frequency greenyellow and cyan lasers are based on intracavity frequency doubled vertical-external-cavity surface-emitting laser (VECSEL), serving as an effective replacement of the legacy dye laser, previously used to address these Ba transition. On the other hand, frequency doubled external cavity diode laser (ECDL) is employed to generate 614 nm orange emission needed for 5D5/2→ 6P3/2 transition. The laser system incorporates modular laser engines together with low-noise driving electronics, mechanical and acoustic concealment and provide laser locking interfaces to high-finesse optical cavity or a wavemeter.


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