Sub-shot noise Laser Gyro

I think that 'entangled photons' in engineer speak translates into 'synchronous detection'. We all know the advantages of that.

I admit to not having read the article yet. I will.

Jeroen Belleman

After all, "entangled" just means interference in a system. It's in a different direction (with respect to particles) than classical interference (time or space). And articles reporting on it almost always get it wrong, so there's that. :^)

Tim

I think in this case it means making the system exactly symmetric with an equal and opposite pair of entangled photons having better properties in terms of their precise frequency when they are combined.

In simple terms classically if you have two photons frequency phi(v) and phi(v+dv) going around the system opposite ways interfering at the end.

But if you can make an entangled mix of them then you get two entangled photons both with frequencies phi(v+dv/2) to first order anyway.

I haven't read the paper yet, but FWIW almost all such schemes that I've seen can in principle improve the SNR over the shot noise *with the same laser power*.

Since the shot-noise-limited SNR increases linearly with laser power, it's usually better (and always much easier) to just hit it harder.

There's a technique called 'quantum illumination' that I don't understand very well, but which gets quantum SNR benefits without being so very sensitive to path loss (as with squeezed states, which unsqueeze again with only a few dB of path loss).

Cheers

Phil Hobbs

Cheers

Phil Hobbs

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in a

Here's the original article (if anyone cares)

As Phil says, the photon count rate for entangled photon system ~10^5/ sec and for typical commercial units, 10^14 photons per second.

It will be a few years. :^)

George H.

I read most of the article "Entanglement-enhanced optical gyroscope" by Matthias Fink , Fabian Steinlechner , Johannes Handsteiner, Jonathan P. Dowling Thomas Scheidl, & Rupert Ursin

The entanglement buzz-word here means that a single photon emission from an atom is close to the place where a second photon was already emitted. They are created out of bonds that touch each other in a crystal at -250 degrees C.

Detecting the single photon coming from one glass fiber is done simultaneously with detecting one photon from another glass fiber. That is very difficult unless few photons are being used. Effectively, only two photons are used in any microsecond of measurements. The authors emphasize that single photons are not measured, but thousands of entangled photons together are measured. So it is only a statistically significant entanglement of large numbers of pairs that is used, and a pair is not useable in this paper.

At room temperature, with a two photon limit, the measurement should occur in a picosecond. Then it is practical. The problem is that standard science uses ancient algebra to describe quantum physics, when that is a sterile, oversimplified model. Experiments, not standard theory, is their only hope for making a product. Or a new theory using 8D geometry.

The authors write, "the resulting measurement advantage is based on the collective behavior of N photons. That is, all N photons are in an equal superposition of being in either one of the two modes of an interferometer, resulting in a shortened de-Broglie wavelength".

I'm not sure what you mean. I skimmed the article. The entangled count rate of 100k/ sec. Suggests to me that they were using the entangled source first described by Paul Kwiat. Here,

about 1/2 down under 'sources of entanglement'. It's a magic x-tal.

George H.