Washington, DC (June 28, 2019)—A group at the National Institute for Standards and Technology (NIST) in Boulder, CO, took a detour from a six-year study of atom-based communications to construct an “atomic recording studio” and demonstrate how quantum physics meets music.
“It is quite amazing that over the past decade we have learned to control ensembles of atoms to such an extent that they can be used to record waveforms,” write the team — Christopher L. Holloway, Matthew T. Simons, Abdulaziz H. Haddab, Carl J. Williams and Maxwell W. Holloway — in a paper recently published by the American Institute of Physics (AIP) named A “real-time” guitar recording using Rydberg atoms and electromagnetically induced transparency: Quantum physics meets music.
Using an acoustic and an electric guitar, a microphone, Audacity software and their quantum system, the team was able to record and play back solo and real-time multitrack performances. They reportedly also captured a stereo recording of Queen’s “Under Pressure” to demonstrate the ability of the system to simultaneously detect the vocal and instrumental parts and record them separately.
The nascent atomic communications technology uses the properties of Rydberg atoms to encode radio waves in a similar manner to cellphone communications. Rydberg atoms incorporate electrons that can be excited to very high energy levels. Changes in the quantum state of those atoms can be detected by lasers, picked up by a photodetector and sent as an electrical signal into a computer for recording or a loudspeaker for playback — in other words, those quantum changes are heard as audio signals.
“This Rydberg-atom based sensor can act as a compact receiver/antenna, enabling quantum-based receivers to be used in communication applications to detect and receive modulated signals,” according to the team’s paper. By using two different atomic species, cesium and rubidium, in the same vapor cell together with lasers of two different wavelengths, the team recorded two guitars and the stereo Queen track to show that a single receiver can pick up two channels simultaneously. This could potentially improve security in future communications systems, according to the team.
“In this approach, we use the output of the guitar to amplitude modulate (AM) a continuous wave carrier,” the paper explains. “While the results in this paper used AM to transit, detect, and record a musical instrument, frequency modulation (FM) of a carrier could also be used. In fact, the AM and FM features of a [signal generator] have been used to transmit and receive AM and FM radio in stereo.”
As for the audio quality, there is some noise, but the NIST team also wanted to show that there was plenty of bandwidth to capture a musical instrument. “A Rydberg-atom receiver has a bandwidth of about 1 MHz to 5 MHz,” the team reports. “Since music is limited to 20 kHz in frequency, the Rydberg-atom based recorder can capture the full musical range of the instrument with high fidelity.”
While the team’s research could lead to the development of atom-based antennas capable of picking up very weak signals transmitted in deep-space communications, they also hope that their atomic recording project will spark the imagination of the next generation of scientists. “Hopefully,” they write, “this ‘entertaining’ example of an application of the sometimes esoteric field of quantum physics may entice individuals to study and apply quantum science to a whole new generation of quantum devices and thereby help create the future quantum-based workforce needed to accelerate the field.”
National Institute for Standards and Technology • www.nist.gov
AIP Publishing • publishing.aip.org