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How many photons are received per bit transmitted from Voyager 1?

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Re: How many photons are received per bit transmitted from Voyager 1?

#51

Post by ramraj07 »

cycomanic wrote: post #43

Actually the limit predicted by Shannon can be significantly beaten, because Shannon assumes gaussian noise, but if we use photon counting receivers we need to use a poisson distribution. This is the Gordon-Holevo limit. To beat Shannon you need PPM formats and photon counters (single photon detectors). One can do significantly better than the numbers from voyager in the article using optics even without photon cpunt…

Can’t you calculate the CRLB for any given distribution if you wanted? That’s what my lab did for microscopy anyway. Saying you’re beating the Shannon limit is like saying you’re beating the second law of thermodynamics to me.. but I could be wrong.

Re: How many photons are received per bit transmitted from Voyager 1?

#52

Post by cycomanic »

Strilanc wrote: post #41

Wasn't expecting my question to hit top of HN. I guess I'll give some context for why I asked it. I work in quantum error correction, and was trying to collect interesting and quantitative examples of repetition codes being used implicitly in classical systems. Stuff like DRAM storing a 0 or 1 via the presence or absence of 40K electrons [1], undersea cables sending X photons per bit (don't know that one yet), some k…

Subsea cables don't use repetition codes (they are very much suboptimal), but typically use large overhead (20%) LDPC codes (as do satellite comms systems for that matter (the dvb-s2 standard is a good example). Generally to get anywhere close to Shannon we always need sophisticated coding.

Regarding the sensitivity of Subsea systems they are still significantly above 1 photon/bit, the highest sensitivity experiments have been done for optical space comms (look e.g. for the work from Mit Lincoln Labs, David Geisler, David Kaplan and Bryan Robinson are some of the people to look for.

Re: How many photons are received per bit transmitted from Voyager 1?

#53

Post by Ringz »

nico wrote: post #46
Strilanc wrote: post #41

Wasn't expecting my question to hit top of HN. I guess I'll give some context for why I asked it. I work in quantum error correction, and was trying to collect interesting and quantitative examples of repetition codes being used implicitly in classical systems. Stuff like DRAM storing a 0 or 1 via the presence or absence of 40K electrons [1], undersea cables sending X photons per bit (don't know that one yet), some k…

Very cool. It’s interesting to realize that at some level, every system is a quantum system if you “zoom in” enough

I would spontaneously respond that you are right and at the same time have no problem if someone explains to me that it is not so.

Re: How many photons are received per bit transmitted from Voyager 1?

#54

Post by BenjiWiebe »

pcdoodle wrote: post #14

I am confused. I thought photons were just visible light but I guess these little buggers are everywhere. Also very surprised voyager is using 2.3ghz, that's crazy saturated on earth due to wifi. How these engineers make this all work, is magic to me.

2.3 GHz is not saturated due to WiFi. Wifi is 2.4GHz and up. Even the harmonics will be above 2.4 GHz (by definition).

Re: How many photons are received per bit transmitted from Voyager 1?

#55

Post by cycomanic »

nico wrote: post #48
cycomanic wrote: post #43

Actually the limit predicted by Shannon can be significantly beaten, because Shannon assumes gaussian noise, but if we use photon counting receivers we need to use a poisson distribution. This is the Gordon-Holevo limit. To beat Shannon you need PPM formats and photon counters (single photon detectors). One can do significantly better than the numbers from voyager in the article using optics even without photon cpunt…

Interesting. Is that related to compressed sensing? I wonder if compress sensing could be used for something like the Voyager signals It seems there might be multiple ways to go beyond Shannon’s limit, depending on what you are trying to do

I don't think compressed sensing is really extracting more information than Shannon, it simply exploits the fact that the signal we are interested in is sparse so we don't need to sample "everything". But this is somewhat outside my area of expertise so my understanding could be wrong.

Re: How many photons are received per bit transmitted from Voyager 1?

#56

Post by layer8 »

ziofill wrote: post #44

What a lovely question. The estimate is 10-100 photons/bit (minimum). If you’re curious about how many bits a single photon can carry, in controlled settings (tabletop quantum optics) a single photon can carry log(n) bits where n is the size of the state space of the photon, which theoretically is infinite and in practice it can reach into the hundreds/thousands.

No, the estimate is around 750 or 200 photons/bit received, depending on the transmission frequency. The answer to the question is B, not C. Your numbers are the estimated minimum needed, not the actual amount received, which is what the question was asking.

Re: How many photons are received per bit transmitted from Voyager 1?

#57

Post by cycomanic »

For anyone who is interested in the ultimate limits to communications the seminal paper by Jim Gordon is quite easy to understand even without a physics degree (unlike the Holevo paper IMO). He was incredibly good at writing in an accessible manner (apart from probably being the person who most deserved a Nobel prize but didn't get it).

https://doi.org/10.1109%2FJRPROC.1962.288169

Re: How many photons are received per bit transmitted from Voyager 1?

#58

Post by empyrrhicist »

nico wrote: post #46
Strilanc wrote: post #41

Wasn't expecting my question to hit top of HN. I guess I'll give some context for why I asked it. I work in quantum error correction, and was trying to collect interesting and quantitative examples of repetition codes being used implicitly in classical systems. Stuff like DRAM storing a 0 or 1 via the presence or absence of 40K electrons [1], undersea cables sending X photons per bit (don't know that one yet), some k…

Very cool. It’s interesting to realize that at some level, every system is a quantum system if you “zoom in” enough

I think the point is the model though - if a system's behavior can be modeled/described classically, it's a bit silly to to call it a "quantum" system in the same way that it's reductive to say Biology is just applied particle physics. Sure, but that's not a very useful level of abstraction.

Re: How many photons are received per bit transmitted from Voyager 1?

#59

Post by mnw21cam »

ziofill wrote: post #44

What a lovely question. The estimate is 10-100 photons/bit (minimum). If you’re curious about how many bits a single photon can carry, in controlled settings (tabletop quantum optics) a single photon can carry log(n) bits where n is the size of the state space of the photon, which theoretically is infinite and in practice it can reach into the hundreds/thousands.

Visible light is different, because each photon has a lot more energy than in the 2.3GHz range. Your average decent consumer-level camera has a sensor that can nominally just about detect single photons some proportion of the time (as in, some of them bounce off instead of being detected) though it can't technically count them. The graininess on digital camera images is more from the Poisson noise of the incoming photons than it is from the applied noise of the sensor itself.

Re: How many photons are received per bit transmitted from Voyager 1?

#60

Post by [deleted] »

ramraj07 wrote: post #51
cycomanic wrote: post #43

Actually the limit predicted by Shannon can be significantly beaten, because Shannon assumes gaussian noise, but if we use photon counting receivers we need to use a poisson distribution. This is the Gordon-Holevo limit. To beat Shannon you need PPM formats and photon counters (single photon detectors). One can do significantly better than the numbers from voyager in the article using optics even without photon cpunt…

Can’t you calculate the CRLB for any given distribution if you wanted? That’s what my lab did for microscopy anyway. Saying you’re beating the Shannon limit is like saying you’re beating the second law of thermodynamics to me.. but I could be wrong.

[deleted]
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