Nature Microsystems and Nanoengineering<\/a>, centers on a manufacturable, silicon-free version of traditional bulky \u201cvapor cells\u201d \u2014 sealed chambers that contain cesium and rubidium atoms \u2014 that are commonly used in precision measurement systems, in a gas state. These atoms can act as highly precise sensors because, unlike manufactured components, atoms are fundamentally identical.<\/p>\n\u201cUsing atoms for sensing is advantageous because the physics of individual atoms is very well understood, and all the atoms are equal,\u201d said Daniel Lopez, co-lead author of the paper, Liang Professor of Electrical Engineering and Computer Science at Penn State and director of the Nanofabrication Lab at the Materials Research Institute (MRI). \u201cThat gives you a level of precision that\u2019s very hard to achieve with traditional microfabricated devices.\u201d<\/p>\n
In the paper, the researchers reported that their cells \u2014 manufactured via a new method similar to the one used to make computer chips \u2014 remained stable over nearly three years of testing, showing that they maintained their internal vacuum and atomic performance over time.<\/p>\n
\u201cYou need to have that gas inside the cavity for a decade so the sensor can work,\u201d Lopez said. \u201cIf you start leaking gas, your detector will stop working.\u201d<\/p>\n
The research also demonstrated that the atoms in their glass cells can measure high-frequency electromagnetic signals, including millimeter-wave radiation, the kind of signal used in advanced communications and radar systems. This precision and sensitivity come from the use of atoms, Lopez said. He pointed to today\u2019s navigation devices, which typically rely on quartz crystals to keep time, as a comparison. These can vary from one to another, drift slightly and need frequent updates from GPS signals to stay accurate.<\/p>\n
Atomic systems are different, Lopez explained. Because atoms are quantum objects, they can keep time much more precisely and stay accurate longer without constantly checking in with satellites. That added stability could improve navigation in situations where GPS signals are weak or unavailable, such as in dense cities, tunnels or remote areas. It could also make technologies like self-driving cars more reliable, since they depend on extremely precise timing to determine location.<\/p>\n
\u201cVapor cells are not new, but they\u2019re historically cylinders made by blowing glass,\u201d Lopez said, explaining that the approach works for laboratory settings. \u201cBut the problem is you cannot integrate that with microelectronics or photonics.\u201d<\/p>\n
The new research addresses that challenge by adopting semiconductor-style fabrication methods to manufacture vapor cells that are smaller, more consistent and at scale. Instead of producing one device at a time, researchers fabricate many at once on flat glass wafers \u2014 extremely thin substrates that help keep the devices stable \u2014 then cut them into individual units. Since researchers can produce many devices at once instead of building them individually, they can reduce manufacturing time, labor and cost while improving consistency.<\/p>\n
\u201cPotentially, this type of fabrication would lower the cost by a lot,\u201d Lopez said.<\/p>\n
The team\u2019s all-glass fabrication process also eliminates silicon entirely, producing sealed vapor cells that are stable over long periods. The devices are made by bonding layers of heat-resistant borosilicate glass and loading them with cesium and\/or rubidium atoms.<\/p>\n
Traditional chip-scale vapor cells often rely on silicon, but that material can interfere with the very signals the devices are meant to measure. Silicon can conduct electricity, which can distort electric fields at high frequencies.<\/p>\n
\u201cIf you want to measure an electromagnetic field with atoms, you need to encapsulate the atoms with materials that do not have electrons that can move,\u201d Lopez said. \u201cGlass is a good example. Silicon is conductive, but with glass, there are almost no electrons there.\u201d<\/p>\n
The researchers also found that the atoms in their glass cells respond to high-frequency electromagnetic signals, including millimeter-wave radiation, the kind of signal used in advanced communications and radar systems. This ability to measure such high-frequency signals could have wide-ranging implications, Lopez said, because today\u2019s classical antennas must be physically sized to match the wavelength of the signals they detect. Atomic sensors, however, can be tuned to different frequencies without changing their size, opening the door to more flexible and compact systems.<\/p>\n
\u201cThe good thing with the atoms is you can make one antenna and you can tune it,\u201d Lopez said. \u201cYou don\u2019t need to change the size.\u201d<\/p>\n
The project was a collaboration between Penn State and NIST, combining expertise in fabrication and measurement science, Lopez said. NIST researchers contributed atomic physics and precision measurement expertise, while MRI provided expertise in materials and advanced fabrication capabilities.<\/p>\n
The work has also attracted interest from industry, including Bullen, a glass company with longstanding ties to MRI. The researchers and Bullen are now exploring potential collaborations to help move the technology toward commercial production.<\/p>\n
Looking ahead, the team plans to integrate these vapor cells with photonic and electronic components, potentially creating fully integrated quantum sensors on a chip.<\/p>\n
\u201cI will say we are just a few years away,\u201d Lopez said.<\/p>\n
In addition to Lopez, Penn State paper authors include Hunter Shillingburg, a graduate student in electrical engineering and computer science; Guy Lavallee, a research engineer with MRI; Miao Liu, former research staff member with MRI; and Chad Eichfeld, a research scientist with MRI. From NIST, authors include Vladimir A. Aksyuk, a research scientist in the Microsystems and Nanotechnology Division; Alexandra B. Artusio-Glimpse, research physicist; Adil Meraki, a physicist with an additional affiliation at the University of Colorado Boulder; Nikunjkumar Prajapati, researcher; Matthew T. Simons, research physicist; Glenn Holland, research engineer; and Christopher L. Holloway, senior scientist.<\/p>\n
The research was supported in part by the NIST.<\/p>\n
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