Cold-atom gyroscopes in three papers

Short answer: A cold-atom gyroscope measures rotation by sending clouds of atoms through an interferometer and reading the phase shift that rotation causes. Three papers, from 2011, 2016 and 2019, report a gyroscope that finds latitude and true north, continuous operation with 100 nanoradians per second per root hertz sensitivity, and interleaved operation with 3 x 10^-10 radians per second stability. These are laboratory instruments.

What did the 2011 gyroscope show?

The 2011 Physical Review Letters abstract reports a cold-atom interferometer gyroscope that overcomes accuracy and dynamic range limitations of earlier atom interferometer gyroscopes. The authors show it can determine latitude, azimuth (true north) and the Earth's rotation rate. Spurious noise terms related to multiple-path interferences are suppressed with a novel time-skewed pulse sequence. They say extended versions appear capable of meeting the stringent requirements for inertial navigation, geodetic determination of Earth's rotation rate, and tests of general relativity. That is a projection, and the abstract reports no such use.

What did continuous operation add?

The 2016 paper reports a cold-atom inertial sensor that continuously captures the rotation signal. A joint interrogation scheme prepares a cold-atom source while operating the interferometer, which eliminates dead times. The authors show that continuous operation improves short-term sensitivity, and demonstrate a rotation sensitivity of 100 nanoradians per second per root hertz in a gyroscope with an 11 square centimetre Sagnac area. They also demonstrate a rotation stability of 1 nanoradian per second at 10^4 seconds of integration time, which they describe as the state of the art for atomic gyroscopes. They say continuous operation will lead to large-area interferometers at their full sensitivity potential, set by the quantum noise limit.

What did interleaving add?

The 2019 Science Advances abstract says cold-atom inertial sensors target navigation, geoscience and tests of fundamental physics, but getting high sampling rates and high sensitivity from long interrogation times is a challenge. The authors report interleaved operation of a cold-atom gyroscope, where three atomic clouds are interrogated simultaneously, with a sampling rate of 3.75 Hz and an interrogation time of 801 milliseconds. Interleaving improves sensitivity by efficiently averaging vibration noise and allows dynamic rotation measurements in a range they call so far unexplored. They demonstrate a stability of 3 x 10^-10 radians per second, which they say competes with the best stability levels obtained with fibre-optic gyroscopes. They add that interleaving is a key concept for future interferometers measuring time-varying signals, as in on-board navigation, gravity gradiometry, dark matter searches and gravitational wave detection. These are the authors' expectations.

How to read this

The three papers report different figures of merit, namely accuracy, sensitivity and stability, from different instruments, so they do not form a single ranking. Lab stability figures say little about performance on a moving platform, which none of the abstracts tests. This post is based on abstracts and visible introductions, and full texts were not checked. It makes no claim about products or navigation systems in use. For other atom-interferometer sensors, see our posts on gravimetry and gravity gradiometry.

FAQ

What does a cold-atom gyroscope measure?

Rotation, through the Sagnac phase shift in an atom interferometer, as the three abstracts describe.

What is the best stability reported?

1 nanoradian per second at 10^4 seconds in 2016, and 3 x 10^-10 radians per second in 2019. They use different averaging methods.

Why interleave clouds?

It averages vibration noise and raises the sampling rate, per the 2019 authors.

Is it used for navigation today?

None of the abstracts says so. They describe navigation as a possible application.