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DARPA Quantum Apertures (QA) developing employing Rydberg atoms for military electronic warfare, radar, and communications.

The world, say many experts, is on the verge of a second quantum revolution. Many scientists believe that quantum will enjoy its first real commercial success in sensing. That’s because sensing can take advantage of the very characteristic that makes building a quantum computer so difficult: the extraordinary sensitivity of quantum states to the environment. Quantum Sensors could be transformative, enabling autonomous vehicles that can “see” around corners, underwater navigation systems, early-warning systems for volcanic activity and earthquakes, and portable scanners that monitor a person’s brain activity during daily life.


Quantum sensing is an area of interest to our military because it is useful on and off the battlefield. For that reason, Army scientists are doing leading-edge research, and exploring the use of quantum sensing for such applications as submarine detection, underwater communications, geolocation, navigation, and communications.


Particularly Researchers are interested in Quantum radio receiver. Radio receiver, a wireless or simply a radio is  an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio waves (electromagnetic waves) and converts them to tiny alternating currents which are applied to the receiver, and the receiver extracts the desired information.


Thanks to the unique advantage of free-space RF field sensing, the quantum receiver has some great advantages compared with conventional electronics based receivers, including but not limited to possibilities of weak signal and long-distance communication in free space or via a fiber link. While Current receivers are only able to receive over a portion of spectrum band or range of frequencies whereas a quantum receiver could give Soldiers a way to detect communication signals over the entire radio frequency spectrum, from 0 to 100 GHz.  Such wide spectral coverage by a single antenna is impossible with a traditional receiver system, and would require multiple systems of individual antennas, amplifiers and other components.


Accurate radio-frequency (RF) electromagnetic field sensing in free-space plays a fundamental role in wireless communication, and Rydberg atoms are remarkable quantum sensors for RF electric(E-) field measurements.  Rydberg atoms created from Rubidium, an alkali metal. Alkali metal atoms are used because they have a single valence electron in the outer shell. The valence electron is weakly bound to the atom because it is the only electron in its energy level and is shielded from the nucleus by the inner core electrons.  Because a Rydberg electron is relatively weakly bound compared to a valence state, it has a comparably stronger response to an electric field.


DARPA launched  Quantum Apertures (QA) program aims to develop a fundamentally new way of receiving radio-frequency (RF) waveforms to improve both sensitivity and frequency agility in several application areas of interest to national security including electronic warfare, radar, and communications.


The teams are set to build on the Rydberg sensors which today are the latest quantum RF aperture technology. Recently developed by the US Army Research Laboratory and previously described as a “super wideband radio receiver”, the Rydberg sensors have some significant advantages over older systems. These sensors and their performance are not constrained by size are not affected by thermal-noise-induced sensitivity issues. Despite this progress, however, researchers still have many technical challenges to address with the new technology.


It is hoped that the program will eventually allow for detecting and processing common waveforms such as digital television and GPS in addition to developing new waveforms.


According to Burke: “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. […] 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.


First demonstrated in the DARPA QuASAR program, the target quantum apertures receivers will sense electric fields using highly excited, so-called “Rydberg” quantum states with high quantum number (n) of approximately 100. High-n states have electrons that orbit ~10,000 times further away from the proton than a ground-state atom, making them highly sensitive to electric fields; effectively acting like small antennae.


In order to detect the electric-field-induced changes in electron orbits caused by the RF electric fields, the QA program seeks to exploit a phenomenon called electromagnetically-induced transparency (EIT) that changes the intensity of a laser passing through a cloud of Rydberg atoms. The QA program aims to develop portable and directional RF receivers useful for future DoD missions with greater sensitivity, bandwidth, and dynamic range than any classical receiver.



In August 2021, the US Defense Advanced Research Projects Agency (DARPA) selected research teams for its Quantum Apertures (QA) program. Leaders for the teams were identified as: ColdQuanta, Honeywell, Northrop Grumman and SRI International.


The goal is to break constraints to antenna designs that have persisted for more than a century, says BAE Systems, reducing size, and increase sensitivity and accessible bandwidth by several orders of magnitude.


According to the company, a quantum approach to aperture development can decouple the size of the antenna from the wavelength of the incoming signal. This can reduce the size and number of antennas on Department of Defense platforms.



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