Cold-atom systems have emerged as a highly promising avenue for quantum-enhanced position, navigation, and timing applications. However, their wider adoption is currently hampered in part by the large footprint of the systems. In leveraging the miniaturisation possible through photonic integrated circuits, cold-atom sensors would be able to reach much wider commercial adoption. In this paper, we introduce a platform for evanescently trapping 87Rb using strip silicon nitride waveguides buried in silica using red- and blue-detuned fundamental and higher-order modes, providing a three-dimensional adjustable trap for BEC-based, chip-scale work in quantum science and technologies.
Cold-atom systems have emerged as a highly promising avenue for quantum-enhanced position, navigation, and timing applications. However, their wider adoption is currently hampered in part by the large footprint of the systems. In leveraging the miniaturisation possible through photonic integrated circuits, cold-atom sensors would be able to reach much wider commercial adoption. In this paper, we introduce a platform for evanescently trapping 87Rb using strip silicon nitride waveguides buried in silica using red- and blue-detuned fundamental and higher-order modes, providing a three-dimensional adjustable trap for BEC-based, chip-scale work in quantum science and technologies.
Photonic circuits are becoming very promising in many different applications, such as optical amplification, optical switching and wavelength division multiplexing optical networks, lab-on-chip in bioengineering, atom-light interaction in quantum information processing, wavelength selecting and filtering in astronomy, etc. Thanks to major developments in the nanofabrication technology, smaller but more powerful photonic circuits can be made to realize more complex applications. Here we propose two on-chip photonic circuits: one is for atom-light interaction in quantum information, and the other is for an optical spectrometer in astronomy. Part I The atom-light interaction can be used for a number of quantum based application, such as quantum information processing and atomic sensing. These significant applications make atom-light interaction a strong candidate for next-generation quantum computers and ultraprecise magnetic or navigation sensors. People have proposed various types of atom-photon interaction, and enhancing the interaction by using a small mode area has also been demonstrated in several platforms such as a hollow-core fiber, a hollow-core waveguide, a tapered fiber, and a nanowaveguide. In our work, we propose a nanowaveguide platform for collective atom-light interaction through the evanescent optical field coupling. We have demonstrated a centimeter-long silicon nitride nanowaveguide that has a sub-micrometer mode area and high fiber-to-waveguide coupling efficiencies for near-infrared wavelengths, working as evanescent field atom trapping/probing of an ensemble of 87Rb atoms. Inverse tapers are made at both ends of the waveguide that adiabatically transfer the weakly guided fiber-coupled mode to a strongly guided mode with an evanescent field for a better fiber-waveguide coupling efficiency. The coupling efficiency improves from around 2% to around 80% for both wavelengths. Trapping atoms by nanowaveguide modes is challenging because the small mode area generates high heat flux at the waveguide in an ultra-high vacuum. This platform has good thermal conductance and could transfer high enough optical powers to trap atoms in an ultra-high vacuum compared to a standalone photonic crystal waveguide with no substrate or an evanescent field coupled with a nanofiber. We have experimentally measured the optical absorption of thermal 87Rb atoms through the guided waveguide mode. We have also demonstrated an atom-chip mirror MOT with the same dimension of the platform that can be transferred to the proximity of the surface by magnetic field controls. Part II In astronomical applications, wavelength analysis is very important especially for the wavelength selecting and filtering. Here we focus on the wavelength range from 1µm to 1.7µm. There are many valuable applications that make this near infrared wavelength range so important. For example, the Lyman-alpha line of hydrogen is one of the very important emission lines of hydrogen for understanding the origin and creation of the universe. Since the universe has expanded for more than 10 billion years after the big bang, the Lyman-alpha line of hydrogen has redshifted from 121.5nm to the 1µm-to-1.7µm wavelength range according to Hubble’s Law. In addition, analysis of this wavelength range can also help us understand many other cosmic phenomena such as quasars, Gamma-ray bursts, etc. Therefore, a good spectrometer is needed to achieve this. Here we present an echelle grating which is based on an on-chip spectrometer that covers the near infrared wavelength range from 1.45um to 1.7um. To begin with, we use optical waveguides as the input and output channels. We have successfully achieved a reliable fabrication process to make the on-chip echelle-grating spectrometer. We have also achieved high fiber-waveguide coupling efficiency (94% per facet at 1550nm) and low propagation loss (-0.975dB/cm at 1550nm) for the input and output waveguides. In addition, we have characterized the bending loss of the waveguide. Finally, we have successfully measured the output spectrum of the echelle grating we designed and found it to be in good agreement with our simulation.
Nanophotonic waveguides are a promising platform to trap cold atoms using red-and blue-detuned evanescent-field optical dipole forces. The asymmetric structure of integrated waveguides leads to a large birefringence that is not encountered in cylindrically symmetric optical nanofibers. We have studied both theoretically and experimentally the modal properties and suitability of silicon nitride rib waveguides for cold-atom trapping. The dependence of the modal effective index on the rib width is explored experimentally by measuring beat lengths between propagating modes. These measurements are made using a novel spatial Fourier analysis technique based on conventional far-field imaging of elastic scattering from the waveguide. We find that the beat length between the lowest order TE00 and TM00 modes is approximately 5µm, in excellent agreement with numerical calculations. We propose to take advantage of this birefringence and mode structure to create novel, one-dimensional periodic trapping potentials for atoms within the evanescent field of the waveguide.
Development of technology can allow access to new regimes in science and creation of new fields of research. The development of ultra-high finesse mirror technology enabled the development of the field of cavity quantum electrodynamics, and an abundance of wonderful physics experiments soon followed. The sophistication of the field of nano-fabrication and nano-photonics would allow unprecedented capability to mold the shape and flow of light, and provide a novel platform for efficient and hopefully integrable quantum systems. In this project, we hope to interface cold atoms, perhaps the most quintessential of quantum systems, to the engineering power of nano-photonics. We believe this field of study will not only lead to the demonstration of new physics in the quantum regime, but work toward building a network with quantum capabilities mediated by optical channels. In this project, we develop a nano-fabricated platform capable of interfacing nano-photonic devices with cold Cesium atoms in free-space. Nano-photonic waveguide devices are fabricated in a Silicon Nitride device layer on Silicon substrate. The fabrication is compatible with conventional semiconductor fabrication processes, and the chip design has been adapted to allow incorporation with free-space optics to support cold Cesium atom cloud around the waveguides. An ultra-high vacuum system that is compatible to the chip and its supporting structures was constructed to perform experiments. With our system, we were able to fabricate and characterize nano-photonic structures, including 1D photonic crystal waveguides, cavities, and 2D photonic crystal slabs. For the 1D photonic crystal waveguide devices, enhanced atom-light coupling between localized Cesium atoms in the vicinity of the devices, and also atom-atom interaction between Cesium atoms mediated by the guided mode of the photonic crystal waveguide, has been observed. The 2D photonic devices allow us many capabilities beyond that of the 1D waveguide. Demonstration of exotic optical properties including natural decay rate suppression and circular polarization engineering, should be within reach in the near future.
Laser-cooled atoms are a key quantum medium for atomic clocks, precision metrology, and atom interferometers, and they hold strong potential to advance quantum technologies for position, navigation, and timing. Realizing this potential requires moving cold-atom systems beyond laboratory environments. Integrated photonic chips provide a path forward by improving reliability and reducing size, weight, and power consumption, enabling portable and compact quantum sensors for real-world applications. This review surveys recent progress in laser-cooled atomic platforms, with a focus on the key components that enable on-chip integration of cold-atom systems. We discuss on-chip laser stabilization and linewidth-narrowing techniques, enhanced photon–atom coupling at the chip scale, miniaturized high-vacuum chambers, and the integration of on-chip magnetic coils for cold-atom sensing. Together, these developments are critical to the deployment of chip-scale cold-atom devices in both fundamental atomic physics and practical sensing applications. We conclude with an outlook on next-generation integrated cold-atom platforms and their potential impact on quantum technologies.
We propose a nanowaveguide platform for collective atom-light interaction through evanescent field coupling. We have developed a 1 cm-long silicon nitride nanowaveguide can use evanescent fields to trap and probe an ensemble of 87Rb atoms. The waveguide has a sub-micrometer square mode area and was designed with tapers for high fiber-to-waveguide coupling efficiencies at near-infrared wavelengths (750 nm to 1100 nm). Inverse tapers in the platform adiabatically transfer a weakly guided mode of fiber-coupled light into a strongly guided mode with an evanescent field to trap atoms and then back to a weakly guided mode at the other end of the waveguide. The coupling loss is −1 dB per facet (∼80% coupling efficiency) at 760 nm and 1064 nm, which is estimated by a propagation loss measurement with waveguides of different lengths. The proposed platform has good thermal conductance and can guide high optical powers for trapping atoms in ultra-high vacuum. As an intermediate step, we have observed thermal atom absorption of the evanescent component of a nanowaveguide and have demonstrated the U-wire mirror magneto-optical trap that can transfer atoms to the proximity of the surface.
Strong atom-photon interactions on scalable photonic platforms hold significant potential for both atomic and photonic quantum information platforms. In particular, trapping of a single atom on a planar photonic integrated resonator at the subwavelength distances required for strong coupling to the guided modes has remained an outstanding challenge. Here we demonstrate efficient trapping of a single ultracold rubidium atom within the evanescent field of an integrated silicon-nitride microring resonator, at distances of 150-200 nm from the chip surface. Efficient, single-stroke loading process is achieved using an evanescent-field mechanism related to Sisyphus cooling, in which a single scattering event dissipates the atom's kinetic energy and transfers it into a near-surface trap. We observe logarithmic scaling of trapping durations spanning from sub-millisecond timescales up to 1 second, without continuous cooling. The trapped atom couples efficiently to the resonator, enabling on-chip photon collection, photon antibunching, and Purcell-enhanced spontaneous emission with single-atom cooperativity exceeding unity. Our results establish the potential of CMOS-compatible chip-based atom-photon interfaces for scalable quantum photonic circuits.