Tiny distances could be measured precisely by using “squeezed” light; Research

Squeezed light could help to detect tiny distances precisely

Researchers have utilized quantum light waves for nanoscale measurements of distances very much precisely not only in standing position but also while the target is moving.

This research has been done by Australian-Japanese research collaboration and published online in the journal Science.

Researchers have worked on the “squeezed” light in an experiment conducted at the University of Tokyo to measure extremely small distances.

“At the heart of all scientific endeavour is the necessity to be able to measure things precisely,” said leader of the international theoretical team Professor Howard Wiseman, from Griffith University’s Centre for Quantum Dynamics.

“Because the phase of a light beam changes whenever it passes through or bounces off an object, being able to measure that change is a very powerful tool.”

“By using squeezed light we have broken the standard limits for precision phase tracking, making a fundamental contribution to science,” he said. “But we have also shown that too much squeezing can actually hurt.”

“The key to this experiment has been to combine “phase squeezing” of light waves with feedback control to track a moving phase better than previously possible,” said Dr Dominic Berry, collaborating author from Macquarie University.

“Ultra-precise quantum-enhanced measurement has been done before, but only with very small phase changes. Now we have shown we can track large phase changes as well,” he said.

“By using quantum states of light we made a more precise measurement than is possible through the conventional techniques using laser beams of the same intensity,” said Professor Elanor Huntington from UNSW Canberra, who directed the Australian experimental contribution. He is one of the colleagues of Professor Wiseman in the Centre for Quantum Computation and Communication Technology.

“Curiously, we found that it is possible to have too much of a good thing. Squeezing beyond a certain point actually degrades the performance of the measurement, making it less precise than if we had used light with no squeezing.” Professor Huntington further said.

You can read the abstract of the paper here,

Tracking a randomly varying optical phase is a key task in metrology, with applications in optical communication. The best precision for optical-phase tracking has until now been limited by the quantum vacuum fluctuations of coherent light. Here, we surpass this coherent-state limit by using a continuous-wave beam in a phase-squeezed quantum state. Unlike in previous squeezing-enhanced metrology, restricted to phases with very small variation, the best tracking precision (for a fixed light intensity) is achieved for a finite degree of squeezing because of Heisenberg’s uncertainty principle. By optimizing the squeezing, we track the phase with a mean square error 15 ± 4% below the coherent-state limit.

Previously, researchers found that squeezed light can help us in the detection of gravitational waves, which are ripples in the spacetime moving away from the source.

Reference:

Hidehiro Yonezawa, Daisuke Nakane, Trevor A. Wheatley, Kohjiro Iwasawa, Shuntaro Takeda, Hajime Arao, Kentaro Ohki, Koji Tsumura, Dominic W. Berry, Timothy C. Ralph, Howard M. Wiseman, Elanor H. Huntington, Akira Furusawa, (2012). Quantum-Enhanced Optical-Phase Tracking. Science, DOI: 10.1126/science.1225258