Entangled-photon gyroscope overcomes classical limit

Entangled-photon gyroscope overcomes classical limit
(Left) Experimental setup and (right) optical design of the fiber-optic gyroscope. Credit: Fink et al. ©2019 IOP Publishing

Fiber optic gyroscopes, which measure the rotation and orientation of airplanes and other moving objects, are inherently limited in their precision when using ordinary classical light. In a new study, physicists have experimentally demonstrated for the first time that using entangled photons overcomes this classical limit, called the shot-noise limit, and achieves a level of precision that would not be possible with classical light.

The physicists, led by Matthias Fink and Rupert Ursin at the Austrian Academy of Sciences and the Vienna Center for Quantum Science and Technology, have published a paper on the entanglement-enhanced fiber-optic gyroscope in a recent issue of the New Journal of Physics.

"We have demonstrated that the generation of entangled photons has reached a level of technical maturity that enables us to perform measurements with sub-shot noise accuracy in harsh environments," Fink told Phys.org.

Fiber-optic gyroscopes (FOGs) are similar to the familiar spinning gyroscopes often sold as toys, as both types of gyroscopes measure an object's rotation. However, the two devices operate using different mechanisms: FOGs have no moving parts, and instead make their measurements using light.

Whereas spinning gyroscopes were developed in the 19th century, FOGs were introduced in the late 1970s and are based on the Sagnac effect that was first observed by Georges Sagnac in 1913. At the time, Sagnac was hoping to detect the ether medium through which light was thought to propagate, but instead his experiment became one of the fundamental tests in support of the theory of relativity.

The Sagnac effect arises when two light beams travel around a ring in different directions in an interferometer. When the interferometer is at rest, both beams take the same amount of time to traverse the ring, but when the interferometer begins to rotate, the beam moving around the ring in the direction of the rotation will travel a longer distance, and therefore take more time, to reach the detector than the other beam. This time difference results in a phase difference between the two beams.

The precision with which a FOG can measure this phase difference determines the precision of the overall rotation measurement. A FOG's precision is limited by several sources of noise, with the major contributor being shot noise. Shot noise arises due to the quantization of the photons. As the individual photons pass through the device, their discrete nature means that the flow is not perfectly smooth, resulting in white noise. Although the shot noise can be decreased by increasing the power (the rate of photons passing through), a higher power increases other types of noise, resulting in a trade-off.

To overcome the shot noise limit, in the new study the physicists used pairs of entangled photons that are in a superposition of the two modes, so that both entangled photons effectively travel through the ring in both directions. The entanglement results in a significant reduction in the de Broglie wavelength of the photons, which in turn leads to a precision that exceeds the shot noise limit, and equivalently, exceeds the best precision possible using classical light.

In its current state, the new FOG is not yet competitive with commercial (classical) FOG devices due to its lower power, which is a consequence of the detectors used. The researchers expect that advances in detector technology and brighter sources will make the entangled-photon FOG feasible for applications in the near future. Overall, they hope that the current results represent an important first step toward achieving the ultimate sensitivity limits in fiber-optic gyroscopes.

"An interesting question is to what extent other noise sources besides the shot noise can be reduced or compensated by using optimized photonic states," Fink said. "The answers to such questions can be experimentally assessed at intensities where such effects become significant."


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More information: Matthias Fink et al. "Entanglement-enhanced optical gyroscope." New Journal of Physics. DOI: 10.1088/1367-2630/ab1bb2
Journal information: New Journal of Physics

© 2019 Science X Network

Citation: Entangled-photon gyroscope overcomes classical limit (2019, May 16) retrieved 21 July 2019 from https://phys.org/news/2019-05-entangled-photon-gyroscope-classical-limit.html
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May 16, 2019
How does an FOG have no moving parts if it depends on a spinning interferometer?

May 16, 2019
How does an FOG have no moving parts if it depends on a spinning interferometer?
The article is confusingly worded for the very people they target who are unfamiliar with optical phase-interference gyros. The gyro doesn't spin, turn, or rotate inside the airplane. It's fixed in the aircraft or satellite and the whole shebang turns. Or to put it another way, the entire aircraft is the gyro. All that counts is the differential in distance of the two light-paths, and any yaw, pitch, or roll will affect that differential of three separate FOG's,  each in their respective planes of airframe rotation.

May 16, 2019
Quote from article: "The entanglement results in a significant reduction in the de Broglie wavelength of the photons, which in turn leads to a precision that exceeds the shot noise limit, and equivalently, exceeds the best precision possible using classical light."

From this description it seems like the two sources of photons going in both directions might actually merge creating a much higher frequency of light. If this were the case wouldn't a higher frequency be able to create a greater precision and exceed the shot noise limit of the lower light frequency introduced into the gyroscope?

If that is the case wouldn't they just be using classical light of a higher frequency?

May 16, 2019
There is something at this link about combining light frequencies of light to create a higher light frequency of light.

http://www.scribd...-Physics />

May 16, 2019
Quote from article: "The entanglement results in a significant reduction in the de Broglie wavelength of the photons, which in turn leads to a precision that exceeds the shot noise limit, and equivalently, exceeds the best precision possible using classical light."

From this description it seems like the two sources of photons going in both directions might actually merge creating a much higher frequency of light.
It's not that they merge and make a higher frequency, but that a biphoton entanglement decreases the de Broglie wavelength; in fact it cuts it in half over that of a single photon. NB the 'de Broglie' part. We're not just looking at frequency or wavelength.

May 16, 2019
Elegant method. The paper is infuriating that it (and other papers I browsed) did not explicitly define "NOON" states, but see their eq 1 why it is called that. It is free, and it is always advised to at least browse the paper for (some) answers to questions.

"... 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 λ/N, where λ denotes the physical wavelength of the individual photons[23]. This leads to an increase of the interferometric fringe pattern frequency by a factor of N (super-resolution)without changing the physical wavelength of the photons ..."

So no increasing light frequencies is used in their setup. In fact, their method of creating entangled photon pairs halves the initial frequency.

May 16, 2019
Having better gyroscopes makes for better piloting -- whether by humans or by autopilots (I'm an amateur human pilot -- for 52 years).

A direct, practical, and very desirable result of applied research in quantum mechanics.

May 17, 2019
Is there not a Tenet of Relativity that the Speed of Light is Relative to this Observer?
phys.org> The Sagnac effect, two light beams travel round a ring in different directions
When this interferometers at rest
both beams take eqal time to traverse this ring
when this interferometer rotates
this beam moving round this ring in the same rotation travels a longer distance
therefore take more time
to reach the detector than the other beam
This time difference results in a phase difference between the two beams

This Oserver
that is this ring moving in the direction of this light beam
the speed of light is relative to this ring
is not travelling a longer distance
but travelling the same distance
as
this ring travelling oppositely
where the light beam is travelling a shorter distance
because relative to this ring
light is not travelling a shorter distance
But travelling the same distance

This Speed of Light is Relative to this Ring; it cannot travel a longer distance

May 17, 2019
Relative Speed of Light

For phase difference caused consternation
it implied that light crossing the same distance oppositely takes different times
proved by their phase difference
Light travelling from ground level to the upper atmosphere while light travelling from the upper atmosphere to ground level by virtue of this orbital earthly speed takes different times indicated by their phase difference
As was pointed out to and by PW physicists resulted in great consternation all round
as this implied this muon crossing the same distance at the same velocity meant it varied this 2.2micro second lifetime
For now we appear to have come full circle back to this same conundrum
that light by virtue of its surroundings crossing the same distance
while travelling at the speed of light
but crossing this distance in different times proved by virtue of its phase shift
Suffice to say everyone knows the result of that forum

Regarded impossible as light speed of is not affected by the emitter

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