> A lot to unpack here...

> * Why is it receive-only?

> Like an antenna, a Rydberg sensor can detect incoming radio signals. Otherwise, the underlying physics are completely different. If there's a way to make it transmit, I've never heard of it.

> * What is the difference between a Rydberg atom, an Ion trap, and a Quantum Dot?

> These are all unrelated devices with different underlying principles.

Ion traps as used in Trapped ion quantum computing involve particles whose wavefunctions are read and written.

Trapped-ion quantum computer:
https://en.wikipedia.org/wiki/Trapped-ion_quantum_computer

Typically trapped ion QC systems are designed to minimize loss and interference. Visible photonic (and other) spectral emissions are certainly caused by changing the wave functions of particles with waveguided EM with and without an additional beam as a waveguide. Is a third beam necessary or useful for modulating particle wave state?

Quantum Dots have spectral emissions due to applied fields.

Quantum Dots are useful as sensors for photonic and other bands.

Rydberg atoms' outer electrons are measurable like Hydrogen electrons.

Single-photon_source#History :
https://en.wikipedia.org/wiki/Single-photon_source#History :

>> Within the 21st century defect centres in various solid state materials have emerged,[9] most notably diamond, silicon carbide[10][11] and boron nitride.[12] the most studied defect is the nitrogen vacancy (NV) centers in diamond that was utilised as a source of single photons.[13] These sources along with molecules can use the strong confinement of light (mirrors, microresonators, optical fibres, waveguides, etc.) to enhance the emission of the NV centres. As well as NV centres and molecules, quantum dots (QDs),[14] quantum dots trapped in optical antenna,[15] functionalized carbon nanotubes,[16][17] and two-dimensional materials[18][19][20][21][22][23][24] can also emit single photons and can be constructed from the same semiconductor materials as the light-confining structures. It is noted that the single photon sources at telecom wavelength of 1,550 nm are very important in fiber-optic communication and they are mostly indium arsenide QDs.[25] [26] However, by creating downconversion quantum interface from visible single photon sources, one still can create single photon at 1,550 nm with preserved antibunching. [27]

The above linked article describes DNA-based quantum dots.

Glass 5x harder than steel for applying atop DNA: https://www.popularmechanics.com/science/a44725449/new-mater...

> *How many 4 or 2 Mhz antenna/transceivers are necessary to sufficiently cover a 0 to 1 Ghz band? What about to cover 1 Thz: (terahertz) band(s)?

> It depends what you mean by "cover".

> Rydberg sensors are tunable over a huge range, typically quoted up to 20-40 GHz. So one sensor would "cover" the whole range of you're willing to wait.

> (I don't know what currently sets that upper limit, but what are you doing that needs more than 40 GHz? Electronics capable of handling such frequencies are rare, specialized, and expensive.)

DSS Digital Spread Spectrum and OFDM Orthogonal Frequency Division Multiplexing use multiple frequencies for transmission (of ~"wave packets") concurrently.

IDK, particle collider sensors that need to monitor for shift across wavelength, phase, and amplitude.

("This means that hard-to-measure optical properties such as amplitudes, phases and correlations—perhaps even these of quantum wave systems—can be deduced from something a lot easier to measure: light intensity." https://news.ycombinator.com/item?id=37226121#37226160 )

Don't e.g. radiotelescopes already cover wider ranges of frequencies than 1 Mhz? The visible colors span more than 1 Mhz.

Terahertz medical imaging is real. https://www.google.com/search?q=terahertz+medical+imaging

Terahertz tomography:
https://en.wikipedia.org/wiki/Terahertz_tomography :

>> Terahertz radiation is electromagnetic radiation with a frequency between 0.1 and 10 THz; it falls between radio waves and light waves on the spectrum; it encompasses portions of the millimeter waves and infrared wavelengths. Because of its high frequency and short wavelength, terahertz wave has a high signal-to-noise ratio in the time domain spectrum.[1] Tomography using terahertz radiation can image samples that are opaque in the visible and near-infrared regions of the spectrum.

> That said, the instantaneous bandwidth of a Rydberg sensor is low, typically around 1 MHz. So if you want to "cover" the whole 0-1 GHz range all at once, I'd start from a different approach.

Is there a bus that can record e.g. 10 Tbit/s of random? So, the task is to do EM ADC/DAC to/from optical fiber?

> *How should they be placed in spacetime to minimize signal loss e.g due to crosstalk and cost?*

> No idea. Each Rydberg sensor requires a lot of expensive support equipment, including two or more precisely tuned lasers.*

The linked article above describes a low cost integrated laser that would probably work for trapped ion quantum computing and also Rydberg sensors:

"Electrons turn piece of wire into laser-like light source" (2022)
https://news.ycombinator.com/item?id=33490730#33493885 re: Surface Plasmon Polaritons and photonic emission

https://news.ycombinator.com/item?id=37335751#37342016 : "Newer waveguide approaches;"

> What are you trying to do?

Get them all! (And filter out bands per legal regulations)

Is it that there need to be 1000x 1 Mhz antennae to monitor for a whole band (linear scaling), or are there potential efficiencies in addition to reducing the cost and size of the electron trap and the laser(s)?