⚛️ quantum physics

MACOR glass-ceramic based UHV cell for quantum technology applications

This paper presents the development and validation of a compact, low-cost, and non-magnetic ultra-high vacuum cell made from MACOR glass-ceramic, which achieves stable pressures below $1 \cdot 10^{-10}$ mbar for over a year, making it highly suitable for field applications in quantum technology.

Original authors: M. Proske, S. Boles-Herresthal, D. Latorre-Bastidas, I. Varma, R. Skanda, O. Hellmig, K. Sengstock, A. Wenzlawski, P. Windpassinger

Published 2026-03-17

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: M. Proske, S. Boles-Herresthal, D. Latorre-Bastidas, I. Varma, R. Skanda, O. Hellmig, K. Sengstock, A. Wenzlawski, P. Windpassinger

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to build a tiny, perfect city for atoms to live in. These atoms are the "citizens" of a quantum computer or a super-sensitive sensor. But these citizens are incredibly fragile; they get sick (lose their quantum properties) if they bump into air molecules or feel a magnetic tug from the walls of their city.

To keep them healthy, scientists build a vacuum chamber—a room with absolutely no air. Traditionally, these rooms are made of heavy metal (like stainless steel) with glass windows. But metal has problems:

It's bulky: Metal walls are thick, blocking the "eyes" (cameras and lasers) scientists need to watch the atoms.
It's magnetic: Metal can mess with the atoms' delicate magnetic states.
It's rigid: You can't easily change the shape of a metal room once it's built.

The Solution: The "Macaroni" City

The researchers in this paper decided to build a new kind of city using a material called MACOR. Think of MACOR as a special, high-tech ceramic that feels like stone but can be carved like wood. It's light, it doesn't conduct electricity, and it's not magnetic.

However, there was a big catch: How do you glue a fragile ceramic city to a metal vacuum pipe without it shattering?

If you try to bolt them together tightly (like tightening a screw on a jar lid), the metal squeezes the ceramic, and crack—the city breaks. If you use standard glue, the glue might leak gas and ruin the vacuum.

The "Cone and Glue" Trick

The team invented a clever way to connect these two different worlds using adhesive bonding and a cone shape.

The Analogy: Imagine trying to join a smooth metal pipe to a ceramic cup. Instead of pressing them flat against each other, they shaped the end of the ceramic into a cone (like an ice cream cone) and the metal pipe into a matching funnel.
The Gap: They made the cone slightly smaller than the funnel, leaving a tiny, invisible gap between them.
The Glue: They filled this tiny gap with a special, high-tech glue (Epotex 353ND). Because the gap is uniform, the glue spreads evenly like honey, creating a perfect seal without putting any crushing pressure on the ceramic.

They did the same thing for the windows. Instead of gluing a window flat onto a surface (which is messy), they carved a little "bowl" (recess) into the ceramic, placed the window inside, and filled the tiny gap around the edge with glue. This ensures the glue doesn't spill onto the glass and block the view.

The Results: A Super-Stable Home

They built a test city (a "science cell") with nine windows of different sizes, allowing scientists to look at the atoms from every angle with high precision.

The Vacuum Test: They pumped all the air out and waited. The pressure dropped to a level where there is almost no air left—so low that if you had a room the size of a football stadium, there would be only a few atoms floating around.
The Longevity Test: They left this setup running for over two years. The vacuum stayed perfect the whole time. No leaks, no degradation.
The Real World Test: They successfully moved cold Dysprosium atoms (a type of heavy metal atom) into this new ceramic city and kept them there. The atoms behaved exactly as they would in a traditional metal room.

Why Does This Matter?

This is a game-changer for the future of quantum technology for three reasons:

Customizable: You can carve MACOR into any shape you want. Need a weird angle for a laser? No problem. Need a specific size? Easy.
Portable: Because it's light and non-magnetic, you can put these vacuum chambers on a truck or even a satellite. This is huge for space applications where weight and magnetic interference are critical.
Cheaper and Easier: You don't need a million-dollar factory to make these. You can machine them with standard tools and glue them together.

In short: The researchers figured out how to build a custom-shaped, non-magnetic, ultra-quiet home for atoms using a special ceramic and a clever gluing technique. It's a cheaper, lighter, and more flexible alternative to the heavy metal boxes scientists have been using for decades, paving the way for quantum computers and sensors that can travel anywhere, even into space.

1. Problem Statement

Modern quantum technology applications, particularly those involving cold atoms (e.g., optical tweezers, microscopy, and quantum sensing), require compact, customizable, and non-magnetic ultra-high vacuum (UHV) systems. Current solutions face several limitations:

Metal Chambers: While standard, metal-to-metal connections (e.g., stainless steel, titanium) are bulky, limit optical access (low numerical aperture), and generate parasitic eddy currents that interfere with magnetic field control.
Pure Glass Cells: While offering excellent optical access and low magnetic interaction, they are expensive, difficult to customize, and challenging to manufacture with double-sided anti-reflection coatings.
Ceramic/Metal Interfaces: Existing ceramic technologies often lack flexibility for laboratory-scale customization or do not integrate optical viewports effectively.
Fabrication Complexity: Alternative approaches (e.g., brazing sapphire into titanium or additive manufacturing) often require specialized infrastructure and extensive post-processing.

The core challenge is developing a low-cost, easily machinable, customizable UHV cell that maintains high vacuum integrity, offers high numerical aperture optical access, and minimizes magnetic and thermal perturbations without requiring complex fabrication infrastructure.

2. Methodology

The authors developed a novel UHV cell using MACOR, a machinable glass-ceramic, combined with adhesive-based bonding techniques to seal the chamber to metal flanges and optical windows.

Material Selection:
- Chamber Body: MACOR (glass-ceramic) chosen for its machinability, low cost, light weight, non-magnetic properties, and electrical insulation.
- Flange: Titanium (selected for its low coefficient of thermal expansion (CTE) mismatch with MACOR, $\Delta \text{CTE} \approx 2 \cdot 10^{-7} \text{K}^{-1}$ between 20°C and 150°C).
- Windows: UV fused silica (low CTE to minimize stress under high-power laser usage).
- Adhesives: Three candidates (Epotek 353ND, H77S, and 377) were evaluated based on Total Mass Loss (TML) at 200°C and viscosity to prevent optical aperture obstruction. Epotek 353ND was selected as the optimal balance of low outgassing and manageable viscosity.
Design Innovations:
- Conical Flange Connection: Instead of direct metal-to-glass compression (which risks cracking brittle materials), a conical mating design was created. A gap is formed between the metal flange and the MACOR body, filled with adhesive. This eliminates high mechanical stress on the sealing surfaces.
- Window Sealing: Windows are placed into recesses within the MACOR body. The recess diameter is slightly larger than the window, creating a controlled gap for adhesive. The window thickness is slightly greater than the recess depth to prevent adhesive from spilling onto the optical surface.
- Thermal Management: The curing process was optimized (slow heating to 80°C rather than rapid 150°C curing) to minimize thermal stress and prevent window breakage.
Fabrication Process:
1. CNC machining of Titanium flanges and MACOR bodies.
2. Ultrasonic degassing of adhesives.
3. Application of adhesive via syringe into the conical and window gaps.
4. Pre-curing at room temperature followed by a controlled bake-out at 80°C.

3. Key Contributions

Novel Sealing Architecture: Introduction of a conical, adhesive-based sealing method that allows for hermetic UHV connections between glass-ceramics and metal flanges without high mechanical stress.
Customizability: Demonstration of a fully customizable science cell geometry (octagonal shape) with nine optical viewports of varying sizes (0.75", 1", and 2"), enabling high numerical aperture access for complex optical setups.
Low-Cost & Scalable Fabrication: Utilization of standard CNC equipment and off-the-shelf materials (MACOR, Titanium, commercial adhesives) significantly reduces fabrication complexity and cost compared to pure glass or specialized ceramic systems.
Material Compatibility: Validation that MACOR is a viable substrate for UHV applications, with potential for future adaptation to other materials like ZERODUR for space applications.

4. Results

Leak Rate: Both test chambers and the final science cell achieved a helium leak rate lower than the detection limit of the equipment: $Q_L < 10^{-11} \text{ mbar} \cdot \text{l/s}$ .
Base Pressure:
- Test chambers achieved base pressures of $\approx 4.3 \times 10^{-10}$ mbar (353ND) and $4.7 \times 10^{-10}$ mbar (H77S) after a 60°C bake-out.
- The final integrated science cell achieved a base pressure of $8.9 \times 10^{-11}$ mbar after a two-week bake-out at 60°C.
Long-Term Stability: The system has maintained a stable pressure of $\le 1 \times 10^{-10}$ mbar for over 23 months (as of the report date) within a cold atom experiment involving Dysprosium.
Experimental Performance:
- Cold Dysprosium atoms were successfully transported 41 cm into the MACOR cell using an optical dipole trap with >60% transport efficiency.
- No degradation in experimental performance or increased background scattering was observed compared to traditional steel chambers.

5. Significance

This work provides a robust, scalable, and cost-effective alternative to conventional metal and pure glass vacuum chambers for quantum technology.

SWaP Optimization: The design significantly reduces Size, Weight, and Power (SWaP) budgets, a critical factor for mobile and space-based quantum sensors.
Magnetic Compatibility: The non-magnetic nature of MACOR eliminates eddy current issues, crucial for experiments involving magnetic trapping or precise magnetic field control.
Future Applications: The technology paves the way for next-generation space-based quantum sensors by demonstrating compatibility with ultra-stable, low-CTE materials like ZERODUR, which can withstand large temperature gradients in space environments.
Accessibility: By using standard machining and adhesive bonding, this approach lowers the barrier to entry for research groups to build custom, high-performance UHV systems without needing specialized glassblowing or brazing infrastructure.