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Simple Mod Turns Diodes Into Photon Counters
KentuckyFC writes "The standard way to detect single photons is to use an avalanche photodiode in which a single photon can trigger an avalanche of current. These devices have an important drawback, however. They cannot distinguish the arrival of a single photon from the simultaneous arrival of two or more. But a team of physicists in the UK has found a simple mod that turns avalanche photodiodes into photon counters. They say that in the first instants after the avalanche forms, its current is proportional to the number of photons that have struck. All you have to do is measure it at this early stage. That's like turning a Fiat 500 into a Ferrari. Photon counting is one of the enabling technologies behind optical quantum computing. A number of schemes are known in which it is necessary to count the arrival of 0, 1 or 2 photons at specific detectors (abstract). With such a cheap detector now available (as well as decent photon guns), we could see dramatic progress in this field in the coming months."
...they treat the earliest stages as if the diode were a unijunction transistor of sorts (using the photon reaction as if it were the gate 'voltage'), and check the waveform? Gah - I'll RTFA(bstract) @ work... :)
Quo usque tandem abutere, Nimbus, patientia nostra?
You kids and your fancy diodes. Back in my day we counted photon by hand. Some people used paper to record the counts. We called them amateurs. Now get off my lawn!
Well, there's spam egg sausage and spam, that's not got much spam in it.
Various people, including Shields himself, have come up with complex, cooled devices that can count photons.
It is the current generation of photon counting detectors which typically require high degrees of cooling (usually with LN2, as you suggest). Photodiodes of the type discussed in the article typically don't have such extreme cooling requirements under normal operation, so presumably that's what's so nice about this mod, as well.
I mean if multiple photons arrive at the same time at the detector should they be counted as a single vote or multiple votes? Whatever you say someone or the other would object and eventually it will be decided in the Supreme Court. Counting is quite weird in Florida.
sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
Something that hasn't been pointed out is how useful this will be in high energy physics. The basic way of measuring a lot of particles is to look for the photons emitted when they interact with materials.
This should help reduce the cost of certain detectors. Especially for measuring neutrinos that can only be spotted by the cherenkov radiation they give off as they pass through massive detectors (look here http://en.wikipedia.org/wiki/Cherenkov_radiation)
So it turns something cheap and unreliable into something most people can't afford that doesn't perform well in crashes?
http://twitter.com/OLDTELEGRAM
There's really no way around cooling the sensor for photon counting, especially if you use near-infrared or lower. If the sensor itself is giving off black-body radiation of the type you're looking for, then it's pretty much worthless to try to count photons because the laws of thermodynamics and quantum mechanics conspire against you. I can imagine visible or UV photon counting with uncooled sensors, but certainly not far-infrared. These thermally-generated photons are what cause the "dark count rate" of a device, and cooling the device can help reduce the dark count rate. Here you are, from wikipedia:
http://en.wikipedia.org/wiki/Single-Photon_Avalanche_Diode
I'd say it's more like finding out your "workstation" is an overpriced, overcomplicated Rube Goldberg device that in reality has the same performance as a Razor scooter.
Up to this point, photon counters were elaborate devices with scintillation media, anticoincidence detctors, veto logic, and complex timing and biasing requirements.
Now you can just apply 9.8V and an instrumentation amp and a couple analog filter/comparator chains, and off you go counting.
I can see the fnords!
This kind of gorgeous tweaking gives me warm feelings inside. Shields has taken a common device used in the field and, through a deep understanding of the physics of its operations, has increased it's functionality without much additional complexity. From the paper he says he cools the device thermo-electrically to -30 deg. C. Thermo-electric cooling is far nicer than cryogenic cooling (typ. using liquid gasses for heat exchange) used in other devices for photon number counting. Further, the method only introduces electronic capacitance subtraction of the photodiode response which is relatively simple compared to other methods (e.g. http://www.stanford.edu/group/fejer/fejerpubs/2005/Langrock_OL_2005.pdf which uses the nonlinear response of a crystal and a massive amount of supporting optics and electronics). This subtraction gives orders of magnitude greater sensitivity and allows the time response of the initial avalanche to be extracted from which photon numbers can be counted. One of those wonderful, "why didn't I think of that", insights. Very nice.
While I can get to the site...I have to question your logic.
Unless /. has some new magics you generally can't post HERE without an active internet connection.
You can get rich if you own a politician, but you have to be rich to buy one in the first place.
You can buy a single photon counter optimized at 680 nm that works at RT. Unfortunately, they are $5k a pop. This way of using avalanche diodes for counting enables a lot of new technologies.
Years ago we played with detecting high energy particles in a grid of scintillating fibers, but for a high precision array you just couldn't afford the detectors. Now I guess I can revisit that if the technology pans out.
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
a lot of the applications for "security" actually is the defeat of cryptanalysis systems as these computers could crack keys in a reasonable amount of time. This would start to drive key length to very large values in order to keep data safe.
Essentially the value in quantum computing is you can set up a logical relationship between all the qbits and then preform an operation on any number of them and they instantaneously effect the remaining qbits. This saves the computation time for preforming operations on all the other qbits. The question on making this feasible is can you make the read/write time for each of the qbits reasonable and the technology affordable to do so. This seems to be a huge step in the right direction for the latter.
Oh honey look... How cute... an angry slashdotter!
Isn't that what those little cells (rods) in our eyes do?
I remember they can detect one single photon, (although we wouldn't perceive it) going all the way up to super bright light.
Although they are more of an analog detector, (stronger signal just looks brighter) rather than digital, it's pretty much the same device.
Actually, your attempt to read the site caused its superposition to decay into a site that's Slashdotted.
About 50% of visitors from Slashdot will see the non-Slashdotted site.
Up to this point, photon counters were elaborate devices with scintillation media, anticoincidence detctors, veto logic, and complex timing and biasing requirements.
Now you can just apply 9.8V and an instrumentation amp and a couple analog filter/comparator chains, and off you go counting.
Single photon avalanche diodes produce rising edge times well under 1ns. You need to measure the *shape* of that rising edge to use this technique. That is a complex circuit, no matter how you look at it.
The new circuits will be vastly simpler. But they will require a fair bit more than instrument amp and a ballast resistor and a comparator.
I think you understand the graph, the presentation is just non-intuitive.
What the graph is saying is that if 0 photons come in, the maximum probability is around 4.5 millivolts. If 1 photon comes in, the maximum probability is about 7.5 mV, and the high end tail of the curve for the 1 photon case is negligible over 11 mV. If 2 photons come in the peak is at 12 mV, and the low end tail of the curve for 2 photons is negligible at 7.5 mV.
In which case what is being shown is that the resting output is around 5mV, and that the pulse height depends on the number of simultaneous photons.
Yep.
If the reading is 7.5 mV, you almost certainly received one photon.
If the reading is 12 mV, you almost certainly received two photons.
If the reading is 9.8 mV, you're 50% likely to have received one or two.
The area under the dark curve can be used to get an idea of the probabilities of any given reading, and most readings are going to be outside the range (from, say, 9 to 10.5) where they're ambiguous.
Smells like a wonderful technology to implement as part of a camera sensor (when dealing with very low light, such as in astrophotography, nightshots of nature, etc.)
Canon's got the "switchable capacitor well" patent hanging in reserve, and it looks like they're going to have to use it with Nikon's new D700 going ASA 6400 and pushing all the way to 25600; but I wonder just how far you could take a camera's sensitivity if you had *accurate* photon counting... imagine a photodetector that counts photons as they arrive and simply increments a large counter. This would literally be a "digital" sensor, rather than an analog one. Precision light sensors. Mmmmm-good. :-)
I like wide-field astrophotography. I'd be all over a (relatively) affordable DSLR that could really do low light in a precise manner. Right now, you have to spend about three grand to get a camera body that can go to an honest ISO 6400; if they could get the price in or around that area with something that was effectively counting all the photons... Oy.
Have to do something about the color and IR filters, too. Swing them out of the way or something equally tricky. Maybe some variation on a single-well, filterless approach like the Foveon one.
I've fallen off your lawn, and I can't get up.
That's no joke. I was going to buy a photon counter for my wife and I to share, but now, I'm going to buy about ten of these for each of us, just in case of a hurricane or something.
Hopefully economies of scale will kick in once these hit the Best Buy shelves.
If moderation could change anything, it would be illegal.
Can some less physics challenged person enlighten me as to how we can actually manipulate a single photon. That to me seems to be such a small amount of energy as to be undetectable. I mean if I remember correctly, if you bounce one electron down from one high level to a lower level on one atom, then, it would give off one photon... and getting one atom to do that seems rather a tall challenge..
This is my sig.
What a strange analogy.
I wonder if a classic car buff would really want to convert their beloved collector's piece into a modern consumerist status symbol for power and wealth?
In any case, while one is fast, and the other is slow, the Fiat was originally made small so that it could navigate the teeny one-lane streets featured in many Italian cities, whereas the Ferrari needs some serious hubcap room. It could be argued that the analogy should be reversed since the smaller car is more agile and able to deal with small details whereas the other cannot and is in fact primarily focused on flying through as many kilometers as quickly as possible and isn't terribly concerned with counting them off in smaller quantities.
Of course, this kind of observation is the reason why I would be irritating at parties. Carry on. I'm listening.
-FL
That's like turning a Fiat 500 into a Ferrari
Ha, thank you, dear Slashdot editor, for inserting a necessary car analogy here! As you rightly guessed, it came right at the point in the summary where my feeble mind wondered "huh?!? photon avalanche wtf???".
Thanks to your enlightening analogy my next thoughts were "ha, a Ferrari, of course! So this has nothing to do with the dangers of skiing on beams of light!", at which point I decided to stop reading the summary as these few concise words seemed to synthesise perfectly the very essence of this discovery, and that my mind proceeded to wander about how awesome it would be to be able to ski on waves of light!
Thank you a thousand times, oh most esteemed and wise Slashdot editor!
You just got troll'd!