Optical fiber gyroscopes, which measure the rotation and orientation of airplanes and other moving objects, have an intrinsic precision as to their accuracy when they use ordinary conventional light. In a new study, physicists experimentally demonstrated for the first time that the use of entangled photons overcomes this classic limit, called the firing noise limit, and reaches a level of precision that would not be possible with conventional light. .
Physicists, led by Matthias Fink and Rupert Ursin at the Austrian Academy of Sciences and at the Vienna Center for Quantum Science and Technology, have published an article on the entangled fiber-optic gyro in a recent issue of New physics journal.
"We have demonstrated that entangled photon generation has reached a level of technical maturity that allows us to perform measurements with subtle sound accuracy in harsh environments," Fink said. Phys.org.
Optical fiber gyroscopes (FOGs) are similar to known spinning gyroscopes often sold as toys because both types of gyroscopes measure the rotation of an object. However, the two devices operate according to different mechanisms: the FOGs have no moving parts and perform their measurements using light.
While spinning gyroscopes were developed in 19th century, the FOG were introduced in the late 1970s and are based on the Sagnac effect observed by Georges Sagnac for the first time in 1913. At the time, Sagnac hoped to detect the ether medium through which the light propagated but his experience has become one of the fundamental tests in support of the theory of relativity.
The Sagnac effect occurs when two light beams move around a ring in different directions in an interferometer. When the interferometer is at rest, the time of passage of the ring is the same for both beams, but when the interferometer starts rotating, the beam that moves around the ring in the direction of rotation travels a longer distance and thus takes longer. time, to reach the detector than the other beam. This time difference causes a phase difference between the two beams.
The accuracy with which an FOG can measure this phase difference determines the accuracy of the overall rotation measurement. The accuracy of a FOG is limited by several sources of noise, the main contributor being the sound of firing. The firing noise comes from the quantification of photons. When individual photons pass through the device, their discrete nature means that the flux is not perfectly smooth, resulting in white noise. Although firing noise can be reduced by increasing the power (the rate of photons passing through), higher power increases the other types of noise, resulting in a compromise.
To exceed the firing noise limit, physicists used in the new study pairs of overlapping entangled photons of both modes, so that the two entangled photons effectively cross the ring in both directions. The entanglement results in a significant reduction in the De Broglie wavelength of the photons, which leads to a precision that exceeds the firing noise limit and, equivalently, exceeds the best possible accuracy with the classic light.
In its current state, the new FOG is not yet competitive compared to commercial (conventional) FOG devices because of its low power, consequence of the detectors used. Researchers expect that advances in detector technology and brighter photon sources will make the entangled photon FOG usable in the near future. Overall, they hope that the current results represent an important first step towards achieving the ultimate sensitivity limits of fiber optic gyroscopes.
"An interesting question is to what extent other sources of noise than firing noise can be reduced or compensated by using optimized photonic states," Fink said. "Answers to such questions can be experimentally evaluated at intensities where such effects become important."
Turning the light: the smallest optical gyroscope in the world
Matthias Fink et al. "Improved optical gyroscope by entanglement." New physics journal. DOI: 10.1088 / 1367-2630 / ab1bb2
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The entangled photon gyroscope overcomes the classical limit (May 16, 2019)
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