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IEEE International Conference on Micro Electro Mechanical Systems (MEMS)

Miniature Quantum Gradiometer Using 3D Interconnected Atomic Vapor Cells

Jianfeng Zhang, Jintang Shang

Published Jan 19, 2025• 0 citations
Publisher

Abstract

This paper, for the first time, reports a miniature quantum gradiometer using a 3D interconnected atomic vapor cells. The Rb vapor cells include two glass bubble vapor cells, with a radius of 1.5 mm, interconnected by channels. This vapor cell provides flexible and extended light path, which is favorable for improving sensitivity and common mode rejection ratio (CMRR) of the gradiometer. Leveraging the flexible optical path, an integrated gradiometer package with a volume of 10.5 cm3is designed. The channel 1 and channel 2 of the gradiometer exhibit a sensitivity of 9.4 pT/Hz1/2and 15.9 pT/Hz1/2at 1 Hz, respectively. And the sensitivity of gradiometer is 16.3 pT/Hz1/2in differential mode at 1Hz.

DOI
10.1109/mems61431.2025.10917793

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This paper, for the first time, reports a miniature quantum gradiometer using a 3D interconnected atomic vapor cells. The Rb vapor cells include two glass bubble vapor cells, with a radius of 1.5 mm, interconnected by channels. This vapor cell provides flexible and extended light path, which is favorable for improving sensitivity and common mode rejection ratio (CMRR) of the gradiometer. Leveraging the flexible optical path, an integrated gradiometer package with a volume of 10.5 cm3is designed. The channel 1 and channel 2 of the gradiometer exhibit a sensitivity of 9.4 pT/Hz1/2and 15.9 pT/Hz1/2at 1 Hz, respectively. And the sensitivity of gradiometer is 16.3 pT/Hz1/2in differential mode at 1Hz.
In this letter, we present a novel microfabricated shaped rubidium vapor cell with 3 cm optical path length for miniaturized atomic magnetometers. The novel shaped rubidium vapor cells are manufactured by a wafer-level fabrication process, and the process consists of the following three steps sequentially: first, wet etching to form oblong shallow cavity arrays; second, anodic bonding, glass reflowing, and wet etching to obtain a glass wafer with shaped structures; third, anodic bonding and chemical reaction to obtain the wafer-level shaped rubidium vapor cells. A miniaturized atomic magnetometer using the novel shaped rubidium vapor cell is characterized in the geomagnetic environment. The performance of the novel shaped rubidium vapor cell is compared with the traditional microfabricated rubidium vapor cell of a “glass–silicon–glass” sandwich structure. Results show that the measured geomagnetic field is 47.85 μT. It is demonstrated that the dispersive signal's slope of the novel shaped rubidium vapor cell is 15 times larger than that of the traditional one. Results also indicate that the miniaturized atomic magnetometer working in the geomagnetic environment has a magnetic noise spectral density of 3.5 pT/Hz1/2from 1 to 2 Hz.
This paper reports the design, fabrication and evaluation of a reflection-type Rb vapor cell with a Glass/Si/Glass structure for chip-scale micro atomic clocks. To miniaturize the cell and obtain a Rb resonance signal with a high sensitivity, long laser light traveling pass on the horizontal plane is required in the vapor cell. The horizontal Rb vapor cell with integrated mirrors are proposed and developed. A (100)-oriented Si wafer with cut off 9.74° toward [011] direction was used to make 45° mirrors by using anisotropic wet etching. Also, 90° mirrors were fabricated by Si deep RIE (Reactive Ion Etching) and H2annealing. Absorption line of Rb was confirmed and CPT (Coherent Population Trapping) resonance was demonstrated in the fabricated devices.
Micro-fabricated vapor cells have applications in a number of emerging quantum technology-based devices including miniaturized atomic magnetometers, atomic clocks, and frequency references for laser systems. Increasing the cell optical path length (OPL) and smallest cell dimension are normally desirable to increase the signal to noise ratio (SNR) and minimize the de-polarization rate due to collisions between atomic or molecular species and the cell walls. This paper presents a fully wafer-level scalable fabrication process to manufacture vapor cells with dimensions approaching those of glass-blown cells. The fabrication process is described, and spectroscopic measurements (optical absorption and magnetic resonance) are reported. A magnetic resonance linewidth of 350 Hz is demonstrated, and this is the smallest linewidth reported to date for a micro-fabricated vapor cell.
The designs of microfabricated alkali vapor cells play an important role when the atomic magnetometers are developing toward on-chip integration. This paper presents microfabricated spherical alkali vapor cells with improved sensitivity for chip-scale atomic magnetometers. A microfabricated spherical rubidium vapor cell and a traditional microfabricated planar rubidium vapor cell are designed for comparison, which are of the same volume and interconnected by a microchannel to acquire equal inner buffer gas pressure. In chip-scale spin-exchange relaxation-free (SERF) atomic magnetometers, the rubidium polarization lifetimes of three pairs of spherical and planar vapor cells at different buffer gas pressures of 0.35, 0.73, and 2.00 amg are measured, respectively. The sensitivity of SERF atomic magnetometers using the vapor cells at a 0.35-amg buffer gas pressure is also measured. The results show that the transverse polarization lifetime of the spherical vapor cell is 2.46, 1.44, and 1.05 times that of the planar one at 0.35-, 0.73-, and 2.00-amg buffer gas pressures, respectively. Combining the improved polarization lifetime and increased optical path length, chip-scale SERF atomic magnetometer using the microspherical vapor cell has the sensitivity of 60 fT/Hz1/2from 5 to 15 Hz, while that based on the planar one is demonstrated with the sensitivity of 400 fT/Hz1/2from 5 to 15 Hz.
Currently, medical magnetic localization necessitates complex and costly gradient coil systems, primarily due to the limited sensitivity of the magnetic sensors in use. This article presents a highly sensitive, compact multipoint quantum magnetometer (CMQM) characterized by a straightforward design and low cost. The core of the sensor is a MEMS 3D Rubidium (Rb) atomic cell with an optical path of 3.0 cm, which is manufactured through a mold foaming process. The size of the compact sensor head is less than 11.5 cm3. The CMQM obtains magnetic field magnitude at six points by measuring Larmor frequency of rubidium atoms within corresponding positions. A uniform magnetic field coils is calibrated with the CMQM within a ferromagnetic shield. The vector synthesis method is used to enhance the accuracy by reducing interference from remanent magnetic field. The deviation between the measured magnetic field and those predicted using closed cylinder approximation (CCA) is less than 1.1%. The magnetic noise density at different points varies between 2.289 pT/Hz1/2and 6.015 pT/Hz1/2. The effective magnetic resolution of the CMQM is ~0.65 nT. Theoretical spatial resolution of the CMQM can reach to$17.5~\mu $m with a simple circular coil. [2024-0230]
Rydberg-atom electrometry, as an emerging cutting-edge technology, features high sensitivity, broad bandwidth, calibration-free operation, and beyond. However, until now the key atomic vapor cells used for confining electric field-sensitive Rydberg atoms nearly made with traditional glass-blown techniques, hindering the miniaturization, integration, and batch manufacturing. Here, we present the wafer-level MEMS atomic vapor cells with glass-silicon-glass sandwiched structure that are batch-manufactured for both frequency stability and electric field measurement. We use specially customized ultra-thick silicon wafers with a resistivity exceeding 10,000 Ω cm, three orders of magnitude higher than that of typical silicon, and a thickness of 6 mm, providing a 4-fold improvement in optical interrogation length. With the as-developed MEMS atomic vapor cell, we configured a high-sensitivity Rydberg-atom electrometry with the minimal detectable microwave field to be 2.8 mV/cm. This combination of miniaturization and sensitivity represents a significant advance in the state-of-the-art field of Rydberg-atom electrometry, paving the way for chip-scale Rydberg-atom electrometry and potentially opening up new applications in a wider variety of fields.