Quantum radar will expose stealth aircraft

> and that isn't the same as what can be done in a small-diameter missile

Which was the genius idea behind Track-via-Missile in the Patriot SAM

Instead of having the missile work-out the best interception based on what it can detect, it relays its view of the World back to the ground station which returns its recommended geometry. Constantly and at high frequency.

And since the ground station is more powerful and can be upgraded more easily than the missile's electronics, Patriot has made huge improvements since the 1991 Scud incidents.

In an anti-stealth context having each missile 'see' from a different angle and being able to fuse that I to one picture is also useful in defeating shaped reflections. It's like a network of remote, lethal sensors.

> Always remember that stealth is not a boolean.

And also it's not just about the technology in the design of the aircraft. It's a combined strategy such as knowing where the radar stations are and flying a path to minimise exposure.

I remember seeing a visualisation of what ISTR was a stealth flightpath into Iraq giving an idea of how they maintained their extremely low visibility. I've just has a search but can't find it at the moment.

"Stealth" is a principal, not a technology. There are a handful of radar techs that defeat traditional stealth technologies that seek to limit reflections, but the principal of hiding from radar is still going to be a thing.

Radars, even quantum radars, each have their issues. The most powerful stealth tech isn't defeating a radar but understanding it well enough to leverage its defects in coverage or operating range. The f-117's real trick was the preflight planning based on a deep understanding of the threat environment. A radar avoided need not be defeated.

We do that now with spread-spectrum and chirps - you correlate the signal sent with the return signal and you can pick out reflections below the noise threshold. https://en.wikipedia.org/wiki/Pulse_compression

I'm guessing that this might be more effective at very small returns, where the reflection is so small that it suffers from shot noise - the fact that the energy comes in discrete packets makes it hard to correlate. This is another way to verify that the photons received are the same ones sent out (and not background noise)

Photons with identical properties are indistinguishable from each other, so not really! You can get really picky about sending out only certain kinds of photon and filtering them when they come back, but you might have some of that kind of photon in the environment anyway, or the target might be capable of generating them to swamp detectors.

What it can't do is generate photons which are entangled with another photon you already have, so it kind of cuts through all the incremental stuff you could otherwise do (and which has been done already).

At least, that's how I understand the physics involved at a fairly superficial level.

This sounds like it's a long way away from being useful though, that slight issue of not having an abundant source of entangled photons is a huge blocker.

They check for entangled photons, as that lets them easily filter out noise inherent in all the other particles.

It's really an idea not a complete system, needing a way to quickly entangle photons on-demand. Cool idea, definitely!, but not yet completed.

Thanks, I remove those bookmarks too. (Being offended gives them more control over you than necessary, in my opinion.)

Latest? L-band early warning has been around for ages. The problem is the range and angle accuracy is not enough to guide an interceptor for fundamental physical reasons: the angular resolution is proportional to frequency and antenna size, and the range resolution is proportional to bandwidth.

> I thought stealth aircraft is already visible on the latest Russian gear

That's just a usual FUD stuff from Russians.

I think that guy has gone too far in pushing against quantum woo. Also, I'm not aware of any actual science that forbids closed time like curves, either; AFAIK they're allowed by GR and anything that rules them out is strictly speculative.

Going slight OT but related is the use of Gravity Anomaly Maps to aid submarine navigation. There are quite a few diverse papers about it but I think information about any real capabilities are largely under wraps.

Scientists who work on atomic clocks believe that they will be able one day to put up a network of quantum-entangled atomic clocks in orbit as a kind of ultra-GPS.

According to an article[1] I read, they should be able to gravimetrically image the volume of earth to within about a cubic centimeter resolution.

At that point it becomes very hard to hide high-density materials, like concentrations of U or Pu, anywhere.

[1] https://www.sciencenews.org/article/quantum-timekeeping

Lol, it's pretty ambitious to try tracking planes with gravitational effects. But now that gravitation wave detection works, I think there are plans (or at least ideas) to build such devices in earth or solar orbit for triangulation of distant objects like stars and black holes. Detection arms could be much longer and disruptions much lower than on earth, so results would me much more accurate.

I ought to start writing scientific papers. I back-of-envelope calculated much the same conclusion years ago — only for the static case, but it was back-of-envelope work.

Yes, so much so that I would not call it a spin-off, rather one of the main tasks that people building quantum computing hardware are dealing with.

Entanglement is one of the main phenomena that permit quantum hardware to do things infeasible on classical hardware. In the context of communication it permits quantum key distribution, whose security depends only on quantum mechanics being a not-too-wrong description of nature (while classical schemes depend on less tested computational complexity conjectures). In the context of computing, it is an integral component of many of the "fault-tolerant error correcting" schemes, necessary in order to protect the extremely fragile qubits (similar to what ECC RAM does for classical computing).

In the context of sensing, it does permit some cool unbelievably sensitive detectors (the case discussed in the article), but it is only one of the avenues of intense research.

"quantum noise bombs"... this wont work as the photons that hit the receiver wont be entangled with the one you sent out... This makes it potentially un-jammable in that sense.

Of course, overloading the receiver may be an attack worthy of investigating.

> What really is horrible here is the asymmetry of cost

That's the fate of most military technologies throughout history, why would stealth be different?

Spam the enemy with thousands of drones.

While it is true that quantum is used a lot as a buzzword, here it is used in its literal scientific sense. And it is an exciting technology that has taken a lot of effort to be created that does not deserve such knee-jerk derisiveness.

Not really. The opsec was poor; the aircraft had been using the same ingress/egress routes, so the SAM batteries knew where to look. That helps tremendously. Also, the F-117 has to open it's bomb bay to release its weapon. When it does so, it increases it's radar return dramatically, if only for a very short period of time. This helped the Serbians a lot.

And passive radar isn't a thing. There's passive radio sensors, that can theoretically detect a transmitter, but frequency hopping etc make that tough.

I'd note that the Serbians kinda lucked out and got it when it was at its least stealthy:

> According to Dani in a 2007 interview, his troops spotted the aircraft on radar when its bomb-bay doors opened, raising its radar signature.