The linewidth of a laser plays a pivotal role in ensuring the high fidelity of ion trap quantum processors and optical clocks. As quantum computing endeavors scale up in qubit number, the demand for higher laser power with ultra-narrow linewidth becomes imperative, and leveraging fiber amplifiers emerges as a promising approach to meet these requirements. This study explores the effectiveness of thulium-doped fiber amplifiers (TDFAs) as a viable solution for addressing optical qubit transitions in trapped barium ion qubits. We demonstrate that by performing high-fidelity gates on the qubit while introducing minimal intensity noise, TDFAs do not significantly broaden the linewidth of the seed lasers. We employed a Voigt fitting scheme in conjunction with a delayed self-heterodyne method to accurately measure the linewidth independently, corroborating our findings through quadrupole spectroscopy with trapped barium ions. Our results show linewidth values of 160 ± 15 Hz and 156 ± 16 Hz, respectively, using these two methods, underscoring the reliability of our measurement techniques. The slight variation within the error-bars of the two methods can be attributed to factors such as amplified spontaneous emission in the TDFA or the influence of 1/f noise within the heterodyne setup delay line. These contribute to advancing our understanding of laser linewidth control in the context of ion trap quantum computing as well as stretching the availability of narrow linewidth, high-power tunable lasers beyond the C-band.
The linewidth of a laser plays a pivotal role in ensuring the high fidelity of ion trap quantum processors and optical clocks. As quantum computing endeavors scale up in qubit number, the demand for higher laser power with ultra-narrow linewidth becomes imperative, and leveraging fiber amplifiers emerges as a promising approach to meet these requirements. This study explores the effectiveness of thulium-doped fiber amplifiers (TDFAs) as a viable solution for addressing optical qubit transitions in trapped barium ion qubits. We demonstrate that by performing high-fidelity gates on the qubit while introducing minimal intensity noise, TDFAs do not significantly broaden the linewidth of the seed lasers. We employed a Voigt fitting scheme in conjunction with a delayed self-heterodyne method to accurately measure the linewidth independently, corroborating our findings through quadrupole spectroscopy with trapped barium ions. Our results show linewidth values of 160 ± 15 Hz and 156 ± 16 Hz, respectively, using these two methods, underscoring the reliability of our measurement techniques. The slight variation within the error-bars of the two methods can be attributed to factors such as amplified spontaneous emission in the TDFA or the influence of 1/f noise within the heterodyne setup delay line. These contribute to advancing our understanding of laser linewidth control in the context of ion trap quantum computing as well as stretching the availability of narrow linewidth, high-power tunable lasers beyond the C-band.
Quantum processors based on ion traps (171Yb+,88Sr+,43Ca+or133Ba+) are one of the key components in the emergence of quantum technologies and have seen their interest explode in the last decade [1]. Although171Yb+ions are commonly used as qubits, a new alternative is based on133Ba+offering several key advantages in terms of lifetime, speed, fidelity and performance. The readout of the qubit is made by shelving the133Ba+ion directly to the metastable 5D5/2 state using a 1762 nm single-frequency laser radiation [2]. For quantum computing and optical qubit manipulation low noise and high-power laser at this wavelength is highly recommended. Thulium doped fiber amplifiers (TDFAs) with broad emission between 1600–2100 nm and high-power capabilities are one of the best candidates for this application. Walasik et al demonstrated a 3W-1762 nm single-frequency TDFA but phase and intensity noise weren't investigated [3].
Quantum phenomena of superposition paved the way for the quantum computer demonstrations utilizing different approaches of qubit creation and manipulation, such as, based on trapped ions, neutral atoms, nitrogen vacancies, photonic integrated circuits, superconducting loops, etc. The trapped-ion-based platform demonstrated record long coherence times, high-fidelity gates, qubit connectivity and potential for fault-tolerant operation [1]. Number of atomic species have been investigated as basis for qubits and various qubit types along with state-preparation and measurement (SPAM) techniques have been developed. These qubit initialization and readout operations as well as atomic ion preparation stages of photoionization and atom cooling are implemented by single-frequency lasers with narrow emission linewidths at frequencies corresponding to electronic transitions in atomic ion specie. Therefore, several single-frequency lasers with well-defined parameters such as linewidth, output power, polarization, intensity noise are required for trapped-ion-based quantum computer. Considering that currently there are about 11 ion species being employed as qubits, thus more than 100 different laser wavelengths are required across the spectrum. For practical use, scalability of quantum computer is required, i.e., steady increase of qubits number without the loss of quantum system control. Therefore, availability and performance of single-frequency stabilized laser systems with tailorable emission parameters is one of pre-requirements for quantum information processing field development and commercialization success.
We report the optical architecture, experimental performance, and simulated performance of polarization- maintaining CW and pulsed single clad Tm-doped fiber amplifiers designed to operate over a wavelength span of 1760—1960 nm. We highlight the potential applications of these amplifiers to quantum computing and quantum qubit experiments using 1762 nm light. Our amplifier exhibits 3 W CW output power and 20 W peak pulsed output power (2 MHz rep. rate, 10% duty cycle) at 1762 nm. Measurements of the wavelength response of the TDFA yield an experimental operating bandwidth extending from < 1750 nm to > 1920 nm. Simulations of the amplifier bandwidth indicate a 3 dB (50% FWHM) wavelength span of 1745 nm to 1980 nm (135 nm). Experimental output power and bandwidth results agree well with the simulations. The external noise figure for this amplifier ranges from 7.5 dB to 9.5 dB. No linewidth broadening was observed in a typical TDFA output when using a single frequency input laser source with a linewidth of 10 kHz. We discuss suitability and applications of the TDFA to 1762 nm enabled manipulation of optical qubits in trapped 133Ba+ ions.
Trapped ions are a leading technology for quantum computing, but their reliance on bespoke tabletop laser and optical systems remains a major obstacle to scaling and robustness. Integrated silicon nitride lasers, compatible with future monolithic integration with surface electrode ion traps, have recently demonstrated frequency-selective qubit state preparation and measurement as well as interrogation of an optical clock transition. However, coherent qubit gates impose even more stringent requirements on laser phase noise, and their implementation with integrated laser sources has remained an outstanding challenge. Here, we use a visible-wavelength integrated Brillouin laser stabilized to an integrated coil resonator to drive coherent single- and two-qubit gates with \Sr optical qubits. We measure an average single-qubit fidelity of 99.61%±0.03% per Clifford gate with randomized benchmarking and use a two-qubit Mølmer-Sørensen interaction to generate an entangled Bell state with a fidelity of 92.35%±1.50%. The qubit exhibits a bare Ramsey coherence time of 659±9μs, more than a tenfold improvement over our previous implementation, which extends to 1.750±0.033~ms with an echo. These results demonstrate, for the first time, that integrated visible-wavelength narrow-linewidth photonic lasers can meet the phase-noise requirements for coherent quantum logic with trapped ion optical qubits, providing a path for scalable optical systems integrated within trapped ion quantum processors.
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.
Integrating precise, stable, ultra-low noise visible light lasers into atomic systems is critical for advancing quantum information sciences and improving scalability and portability. Trapped ions are a leading approach for high-fidelity quantum computing, high-accuracy optical clocks, and precision quantum sensors. However, current ion-based systems rely on bulky, lab-scale precision lasers and optical stabilization cavities for optical clock and qubit operations, constraining the size, weight, scalability, and portability of atomic systems. Chip-scale integration of ultra-low noise lasers and reference cavities operating directly at optical clock transitions and capable of qubit and clock operations will represent a major transformation in atom and trapped ion-based quantum technologies. However, this goal has remained elusive. Here we report the first demonstration of chip-scale optical clock and qubit operations on a trapped ion using a photonic integrated direct-drive visible wavelength Brillouin laser stabilized to an integrated 3-meter coil-resonator reference cavity and the optical clock transition of a 88Sr+ ion trapped on a surface electrode chip. We also demonstrate for the first time, to the best of our knowledge, trapped-ion spectroscopy and qubit operations such as Rabi oscillations and high fidelity (99%) qubit state preparation and measurement (SPAM) using direct drive integrated photonic technologies without bulk optic stabilization cavities or second harmonic generation. Our chip-scale stabilized Brillouin laser exhibits a 6 kHz linewidth with the 0.4 Hz quadrupole transition of 88Sr+ and a self-consistent coherence time of 60 μs via Ramsey interferometry on the trapped ion qubit. Furthermore, we demonstrate the stability of the locked Brillouin laser to 5×10−13/τ at 1 second using dual optical clocks.