Manufacturing Bits: Aug. 9

Quantum RF sensors
The quantum computer market is an emerging and hot business. So is the quantum sensor market, where several entities are developing this technology for a range of applications.

“Quantum sensors utilize quantum states for measurements,” according to Chalmers University of Technology. “They capitalize on the fact that quantum states are extremely sensitive to disturbances – this means that they also have the potential to become extraordinarily sensitive measuring instruments.”

Quantum sensors are used in several applications. These components could be incorporated in measurement instruments, RF systems and others. These systems promise to overcome the limitations of today’s technologies.

In one example of this effort, the Defense Advanced Research Projects Agency (DARPA) has launched a program that will propel the development of RF quantum sensors.

The project, called the Quantum Apertures (QA) program, is led by Honeywell, Northrop Grumman, ColdQuanta, and SRI International. The group will develop portable and directional RF receivers with greater sensitivity, bandwidth, and dynamic range than classical RF technologies. The project will advance the development of a quantum RF sensor technology called the Rydberg sensor.

RF is widely used in today’s commercial, industrial and military systems. “Today, commercial wireless infrastructure, the construct of spectrum use, and beyond have been dictated by a hundred years’ worth of antenna theory, originally developed by German physicist Heinrich Hertz,” said John Burke, the program manager leading the QA program at DARPA. “With the introduction of quantum, we have the ability to replace the existing fundamental limits placed on antenna technology with a whole new set of rules. Quantum Apertures seeks to create a paradigm shift in the way we access and use the spectrum.”

The program will advance the development of Rydberg sensors. “The Rydberg sensor uses laser beams to create highly-excited Rydberg atoms directly above a microwave circuit, to boost and hone in on the portion of the spectrum being measured,” according to the Army Research Laboratory (ARL). “The Rydberg atoms are sensitive to the circuit’s voltage, enabling the device to be used as a sensitive probe for the wide range of signals in the RF spectrum.”

Ryberg sensors have several advantages over today’s antenna-based receivers. Ryberg sensors have higher sensitivities and less noise. “Ryberg sensors have no such size limitations with respect to the received RF frequency wavelength,” according to DARPA. “This decoupling of the aperture shape and RF frequency enables a Rydberg sensor to be programmed over a large frequency range – from MHz to THz.”

Researchers in the QA program plan to demonstrate a portable RF receiver system using Rydberg sensors. The system will be able to operate over a large spectral range – from 10MHz to 40GHz, or more—with only one antenna. Researchers will also develop a sensor element and its associated electronics in a one cubic centimeter package, which can operate across all frequencies. Further, the sensor will utilize lasers instead of cable for wiring, making it more resilient to high-power effects and tolerant of microwave radiation.

“Recent demonstrations of Rydberg atomic sensors have shown that it’s possible to access large portions of the RF spectrum, but QA aims to go beyond those efforts by continuously connecting these demonstrations across the spectrum,” noted Burke. “We’re going from simple demonstrations of one functionality to a device that can be programmed to do almost anything and do most of it better than a classical receiver could. This includes speeding up the time to tune the sensor, improving sensitivity to small signals, enhancing dynamic range, and expanding compatibility with modern signals.”

Quantum receivers
The Army Research Laboratory (ARL) has recently developed a quantum receiver.

This technology could pave the way towards a new class of sensors in defense applications, such as electronic warfare, sensing and communications. It could one day give soldiers on the battlefield a way to detect communication signals over the entire RF spectrum in a single system.

In the lab, ARL combined an atomic RF receiver and spectrum analyzer. At the heart of the system is a thermal Rydberg sensor. The spectrum analyzer “achieves an intrinsic sensitivity of up to −120, dc coupling, 4-MHz instantaneous bandwidth, and over 80 dB of linear dynamic range,” according to ARL in Physical Review Applied, a technology journal.

By attaching an RF antenna on the system, ARL’s spectrum analyzer can detect signals in the entire RF spectrum — from zero frequency up to 20GHz — and detect AM and FM radio, Bluetooth, Wi-Fi and other communication signals.

“All previous demonstrations of Rydberg atomic sensors have only been able to sense small and specific regions of the RF spectrum, but our sensor now operates continuously over a wide frequency range for the first time,” said Kevin Cox, a researcher at ARL. “This is a really important step toward proving that quantum sensors can provide a new, and dominant, set of capabilities for our soldiers, who are operating in an increasingly complex electro-magnetic battlespace.

“Significant physics and engineering effort is still necessary before the Rydberg analyzer can integrate into a field-testable device,” Cox said. “One of the first steps will be understanding how to retain and improve the device’s performance as the sensor size is decreased. The Army has emerged as a leading developer of Rydberg sensors, and we expect more cutting-edge research to result as this futuristic technology concept quickly becomes a reality.”

Dark matter
The National Institute of Standards and Technology (NIST) has developed a new quantum sensor, a technology that could detect signals from dark matter.

In theory, 4.9% of the universe consists of observable matter, such as protons, neutrons and electrons. Then, some 68.3% of the universe is dark energy, while the remaining 26.8% is dark matter. So, dark matter exists in the universe, but it is invisible to the entire electromagnetic spectrum. To date, though, researchers have failed to directly observe or detect dark matter.

There are several entities looking for dark matter in various labs worldwide. If one can find or detect dark matter, it may give researchers a better understanding of the origins of the universe and matter.

NIST’s quantum sensor consists of 150 beryllium ions confined in a magnetic field. The ions are configured in a flat 2D crystal just 200 millionths of a meter in diameter.

This sensor can measure external electric fields that have the same vibration frequency as the crystal with more than 10 times the sensitivity of any previously demonstrated atomic sensor.

“Ion crystals could detect certain types of dark matter — examples are axions and hidden photons — that interact with normal matter through a weak electric field,” said John Bollinger from NIST. “The dark matter forms a background signal with an oscillation frequency that depends on the mass of the dark matter particle. Experiments searching for this type of dark matter have been ongoing for more than a decade with superconducting circuits. The motion of trapped ions provides sensitivity over a different range of frequencies.”

Related
The Great Quantum Computing Race
Companies and countries are pouring tens of billions of dollars into different qubit technologies, but it’s still too early to predict a winner.