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China Says It Has Developed a Quantum Radar That Can See Stealth Aircraft (digitaltrends.com)
An anonymous reader quotes a report from Digital Trends: At a recent air show in the city of Zhuhai, state-owned Chinese defense giant China Electronics Technology Group Corporation displayed what it claims to be a quantum radar that's able to detect even the stealthiest of stealth aircraft. The company claims to have been working on the technology for years, and to have tested it for the first time in 2015. In principle, a quantum radar functions like a regular radar -- only that instead of sending out a single beam of electromagnetic energy, it uses two split streams of entangled photons. Only one of these beams is sent out, but due to a quirk of quantum physics both streams will display the same changes, despite being potentially miles apart. As a result, by looking at the stream which remains back home it's possible to work out what has happened to the other beam. According to a brochure from the China Electronics Technology Group Corporation, the new quantum radar could "solve the traditional bottleneck [of] detection of low observable target detection, survival under electronic warfare conditions, [and] platform load limitations."
They wouldn't admit this to the world if they really had it, and it really worked. Sounds like another Chinese hack to me.
The article gives a pretty poor, if not outright wrong, explanation of what quantum radar is supposed to be. The idea behind quantum radar is that the microwave signal sent out by the radar system is first generated by one half of an entangled photon beam, and this is done in a way that maintains the quantum state as the photon beam is converted into a microwave signal. When the microwave signal returns after bouncing off a target object, the system is then able to use a comparison to the other half of the entangled photon beam in order to filter out any background noise. This would prevent an enemy from being able to using signal jamming to interfere with your radar. It would also make it easier to detect a stealth aircraft because no stealth aircraft is 100% invisible to radar, and quantum radar would, in theory, be able to pick out very small radar returns, that would normally be lost in the background radiation.
There are three parts to their claim and they're all pseudo-babble junk:
1. A "stream of photons" can detect a stealth aircraft from some useful distance
2. Photons can be entangled on the fly (in real "stream" speed)
3. The entangled stream at home can be analyzed on the fly (same speed)
1.
Can photons be entangled? Sure. Can they be entangled at the speed of light such that a "stream of photons" (going out sequentially at the speed of light) are all entangled... possibly, but not with current technology and not with 2015 technology.
Think of it this way... physicists spend days setting up a quantum entanglement experiment where they entangle ONE or even TWO and sometimes FOUR (http://iopscience.iop.org/article/10.1088/1402-4896/aa736d) photons. To entangle enough to create a "stream of photons" and then sweep the skies two or three dimensionally for stealth aircraft is orders of magnitude beyond current tech.
2. It takes experiments ages (in photon time) to get photons entangled. Our primitive tools (electronics) uses electrons in a wire, which are slower than photons in air or in vacuum. Our tools simply cannot hammer these fast-moving nails fast enough... so what we do is fire a crap-ton of nails at our slow moving hammer and hope we can hit one into the other into the detector.
3. See #2. We don't have the speed with our slow-moving tools to analyze a photon stream.
I'm calling physics bullshit.
Ehud
Not at all. In modern world, warfare generally uses two different radar types - search radar which you can see spinning around in at 360 degrees and fire control radar that uses a directional pulse/beam. Problem with stealth is that it can be tracked by radar with low accuracy, i.e. you can get the general direction where aircraft is on your search radar, but you can't get a high accuracy track needed for fire control radar to be effective. So detection of stealth aircraft isn't a problem for modern radar systems. Tracking them accurately is.
That means that if you can develop a fire control radar that can produce a track accurate enough for a missile to be effective, stealth becomes effectively reduced or even nullified for purposes of anti-air warfare.
The article's description is flat our wrong. The idea behind quantum radar is that the photons used to generate the microwave signal are first entangled with photons that are kept inside the system, and then when the system receives returning microwaves, it's able to compare them to the entangled photons and filter out background noise and enemy jamming signals. The filtering out of background noise is what in theory would allow quantum radar a greater chance to detect stealth aircraft, which normally rely on background noise to obscure their small radar cross section. That being said, just because the Chinese say they've invented it, obviously doesn't mean they have. In fact, I would guess if any major power does develop a working quantum radar, they'd keep it secret.
In particular, the quantum radar does not claim any FTL nonsense. A beam is sent out, and reflected from the target. A very weak reflection, in case of a stealth plane. The quantum radar is not faster, it is merely able to see that extremely weak reflection because it is not hampered by background noise (natural microwave noise or electronic warfare jammers).
Read the wikipedia article on quantum radar. The principle is so old it has a wikipedia page - the only "new" here is that China claims they have a working device. I would guess some others have these devices too, but are quiet about them.