Low-Power Evanescent-Field Atom Guides on Optical Nanofiber Testbeds for Benchmarking Membrane-Waveguide Photonic Integrated Circuit Platforms Toward On-Chip Quantum Inertial Sensors

Abstract

Recent advances in cold atom interferometry with atom guides have set the stage for miniaturized quantum inertial sensors capable of operating in dynamic environments. In this work, we combine three key innovations - evanescent-field (EF) atom guides, optical nanofiber (NF) testbeds, and membrane-waveguide photonic integrated circuit (PIC) platforms - to advance EF-guided atom interferometry. First, we demonstrate the feasibility of EF atom guides on optical NF testbeds, providing a mean to benchmark membrane-waveguide PIC platforms. Second, we achieve low-power (~5 mW) guiding of freely moving, laser-cooled 133Cs atoms in two-color, traveling-wave EF optical dipole traps at the magic wavelengths of 793 nm and 937 nm - referred to here as 793/937-nm EF atom guides - in contrast to conventional 685/937-nm standing-wave EF optical lattices. The 793/937-nm EF atom guides map directly onto the membrane-waveguide PIC platforms, which can safely handle up to 4-6x times the minimum trap power under vacuum and enable dense cold atom generation for efficient loading into the EF atom guides. Third, we verify preserved atomic coherence via microwave fields and EF-coupled Doppler-free Raman beams. To our knowledge, this is the first report of coherence fringes driven by co-propagating EF-coupled Raman beams with only 150 nW of total optical power. By forging a direct link between optical NF testbeds to membrane-waveguide PIC platforms, our results lay critical groundwork for the on-chip realization of EF-guided atom interferometry and for fully integrated, low-SWaP (size, weight, and power) quantum accelerometers and gyroscopes.

Figures (12)

• Figure 1: Evanescent-field (EF) atom guides (i.e. EF optical dipole traps) on membrane-waveguide photonic integrated circuit (PIC) platforms and optical nanofiber (NF) testbeds. (a) Illustration of the membrane waveguide (WG), EF atom guide, and EF-guided atoms; the WG geometry is characterized by the width ($\rm{W_{WG}}$), thickness ($\rm{T_{WG}}$), and membrane thickness ($\rm{T_{MEM}}$). (b) Illustration of the optical NF, EF atom guide, and EF-guided atoms; the NF's geometry is defined by its diameter ($\rm{D_{NF}}$).
• Figure 2: On-chip quantum inertial sensors based on EF atom guides on membrane-waveguide PIC platforms, and their EF-guided atom interferometry protocols using EF-coupled light-pulse sequences. (a) A quantum accelerometer utilizes linear membrane waveguides. (b) A quantum gyroscope employs racetrack membrane waveguides. (c) Linear acceleration measurement protocol involves three light pulses ($\frac{\pi}{2} \rightarrow$ T $\rightarrow \pi$$\rightarrow$ T $\rightarrow \frac{\pi}{2}$), where T represents the interrogation time. (d) Angular velocity measurement protocol utilizes two light pulses ($\frac{\pi}{2} \rightarrow$ T $\rightarrow \frac{\pi}{2}$). These light pulses impart state-dependent photon recoils to the EF-guided atoms, enabling precise measurements of linear acceleration and angular velocity. Red and blue filled circles (or annular sectors) denotes the two atomic states.
• Figure 3: Optical potential of the EF atom guide on two platforms: (a) a membrane-waveguide PIC platform and (b) an optical NF testbed. In both cases, the EF atom guide is formed by blue-detuned (793 nm) and red-detuned (937 nm) traveling evanescent waves, yielding a trap depth of approximately 350µ K at the 852nm $\rm{D_2}$ transition of 133Cs atoms (the first and second rows of \ref{['tab:trap_comp']}).
• Figure 4: Alumina ($\rm{Al_2O_3}$) membrane-waveguide PIC platforms in hybrid-needle and infinity designs, and specialized geometries for area-enclosed matterwave interferometers. (a) Hybrid-needle design: a suspended membrane waveguide spans two silicon (Si) needles with undercut trenches. (b) Infinity design: a membrane waveguide is defined between two adjacent holes whose edges nearly touch. (c) Omega-shaped platform: semi-enclosed loop for circular atom guiding (1.4mm span). (d) Ring-shaped platform: fully enclosed Sagnac loop (700µ m span). Panels (c) and (d) show the devices before $\rm{XeF}_{2}$ release: off-white regions become open gaps, blue regions remain as alumina membrane and membrane waveguides above the Si structures, and brown regions form suspended membrane. (e) Released omega platform mounted on a glass slide, featuring a membrane waveguide taper for circular atom guiding and improved heat dissipation. The inner rectangular opening area (9mm$\times$9.6mm) enables dense cold atom generation near the EF atom guide. (f) Fiber trench cutout with rounded corners: protects the waveguide facet during $\rm{XeF}_{2}$ etch, maintain facet tension, and support efficient free-space coupling.
• Figure 5: Calculation of the light shift (LS) for 133Cs energy levels as a function of trap wavelength (nm) in vacuum for $\pi$ and $\sigma^{+}/\sigma^{-}$ polarizations: (a) LS for the 6S$_{1/2}$$\ket{F=4}$ and 6P$_{3/2}$$\ket{F'=5}$ transition with 793-nm light. (b) LS for the 6S$_{1/2}$$\ket{F=3}$ and 6P$_{3/2}$$\ket{F'=4}$ transition with 793-nm light. (c) LS for the 6S$_{1/2}$$\ket{F=4}$ and 6P$_{3/2}$$\ket{F'=5}$ transition with 937 nm light. (d) LS for the 6S$_{1/2}$$\ket{F=3}$ and 6P$_{3/2}$$\ket{F'=4}$ transition with 937 nm light.