A new antenna using single atoms could usher in the age of atomic radio | Hacker News Reader

A new antenna using single atoms could usher in the age of atomic radio

arstechnica.com

91 pointsvezycash19 comments

The phrase "single atoms" seems misleading. The article describes the primary device as a cell containing a vapor that needs a laser to activate the gas and a laser to measure the gas. As far as I can tell the only thing "single" here is that the vapor consists of one type of element, which doesn't seem like an important piece of information for the title.

Edit: "single atoms" -> "gas and lasers"

Here is an alternate source with more concise details and a nice diagram of the lasers and the cell.

https://www.technologyreview.com/s/611977/get-ready-for-atom...

This is really interesting, but I am a bit confused on the practical implementation. How could this be used to replace real-life systems? If I understood it correctly, a potential system would be made up of lasers at the transmitters, and a cloud of Rydberg atom gas at the receiving end plus a specifically tuned laser to saturate the gas.

But this design runs into line-of-sight issues between the receiver and transmitter. Also, the Rydhberg gas needs to be contained in some way that will hold the gas in whatever place it needs to be but also be transparent such that the transmitting laser can impact the gas as required without interference from the containing medium.

I feel like this is conceptually cool, but not useful/practical outside of a lab or unrealistically perfect outdoors environment. Does anyone know of any uses for this new tech?

The signals are not transmitted with lasers, they are transmitted with traditional RF broadcasting equipment. This is just an AM/FM radio receiver that detects RF with lasers. The breakthrough is that it doesn't require a physical antenna proportional in size to the wavelength of the frequency it is detecting.

Interesting. But I had never before heard a description of RF ranges in octaves. I suppose it makes sense, but that completely threw me off because I thought they were talking about sound waves for a second.

All waves are based in the time domain (space between waves), half or double space is an octave. Slighty unusual, but not very. I hear musical terms used a lot when it comes to analog signals. (Yes, even 'digital' signals need an analog carrier).

> never before heard a description of RF ranges in octaves

you can read something about filter designs...

> It is usual to measure roll-off as a function of logarithmic frequency, consequently, the units of roll-off are either decibels per decade (dB/decade), where a decade is a 10-times increase in frequency, or decibels per octave (dB/8ve), where an octave is 2-times increase in frequency.

https://en.wikipedia.org/wiki/Roll-off

I hear it fairly often in discussions about passives that operate in a frequency range excluding DC. If the geometry defines the frequencies, the upper and lower frequency limits will have a fixed ratio as you scale the device up/down. For instance, textbook directional couplers typically have octave range (1-2GHz, 2-4GHz, 10-20GHz) while "clever" couplers can have decade range (1-10GHz) or more. Similar stories apply to cavity or microstrip filters/resonators.

Since frequency and bandwidth are banner specs the terms often leak into the names themselves -- someone might advertise a "multi-decade coupler" and compare it to "octave couplers." You can readily find examples on google.

Harmonics are a key concern in RF but I usually hear the terms "fundamental, second, third, etc" used to refer to them and it would sound odd to my ear if someone used "octave" in that context.

The market price for a pair of tunable lasers to do this is more than $100k.

Very small, but needs a large “backup system”? So, not very small. And what exactly is this backup system?

Ok, I've been downvoted. But I'm still curious what in the world could be considered a "backup system" but also necessary for implementing the technology. Anything necessary for it to work isn't a "backup" is it?

And I'm also still curious what this particular large "backup system" is.

Does that mean we should have SETI looking into other channels?

Antenna engineer here. The metal antennas mentioned in the article are resonant (standing wave) antennas. There is another class of antennas called traveling waves, but still need to be about 1/2 wavelength to operate efficiently.

That being said, antennas can be much smaller than 1/2 wavelength, but their efficiency goes down. There is a theoretical limit trading off bandwidth and efficiency for volume, called the Chu limit.

So it would be interesting how this technique compares. It says it’s narrow band, so like a laser, which means it may still be limited.

There are other methods, such as bouncing a laser off a thin metal membrane, which supposedly has very low noise. Wonder how noisy this method is?

Antenna noise temperature is related to efficiency, but this is an active antenna. So it really boils down to bandwidth vs. noise temperature per volume. That metric would give an indication of how it compares to classical antennas.

Any introductory reading you might recommend?

There are a couple of books on electrically small antennas, but those are not introductory. Stutzman and Theile is a good antenna textbook, and there are many others; John Krause for example.

You could start with the ARRL Antenna Compendium, for non-engineering books.

Steven Best has some good papers (i.e. the spherical folded dipole), if you have access to IEEE Xplore. The APS magazine articles are very good.

I meant basic, standard, antenna engineering.

Though the small stuff is also interesting.

Thanks.

Might want to try

Antenna Theory - Analysis and Design - Balanis (2016)

But noticed a 2005 3rd edition is available in .pdf for download gratis at:

https://archive.org/details/AntennaTheoryAnalysisAndDesign3r...

Thanks, this and the above are a good start.

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