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 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].
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.
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.
We report a fully fibered, polarization-maintaining, single-frequency thulium-doped fiber amplifier operating between 1730 and 1762 nm and delivering more than 30 W of output power. Relative intensity noise is preserved after amplification, with a noise floor of -158 dBc/Hz between 100 kHz and 4 MHz. These results demonstrate the suitability of this source for quantum technology, including direct operation within the tuning range at 1762 nm for barium ion excitation or a possible nonlinear frequency conversion toward 813 nm for strontium atom trapping.
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.
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.