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Dr. Kitagawa’s paper selected as one of Physical Review A 50th Anniversary Milestones

2020-11-10(Tue)

A paper entitled “Squeezed spin states” by Dr. KITAGAWA Masahiro (Director, Quantum Information and Quantum Biology Division, Institute for Open and Transdisciplinary Research Initiatives /Professor, Graduate School of Engineering Science) was selected as one of the collection of milestone papers by Physical Review A 50th Anniversary Milestones.

Physical Review A 50th Anniversary Milestones is a collection of milestone papers that have made important contributions to atomic, molecular, and optical physics and quantum information by announcing significant discoveries or by initiating new areas of research. Many of these papers have greatly influenced other subjects of physical sciences. 26 papers from the past 50 years will be selected, and of the 22 selected so far, Professor Kitagawa’s paper is the only one selected from Japan.


The uncertainty (black portion) is deformed and squeezed in one direction by one-axis twisting like wringing a towel

Comment from Professor Kitagawa

In quantum mechanics, the exact position and momentum of an electron cannot be simultaneously determined, and the Heisenberg uncertainty principle gives a non-negative lower bound on the product of the uncertainty in the position of a quantum particle and its momentum.

For example, the amplitude of a light wave (sine or cosine) has uncertainties. Reducing the uncertainty of one of these light wave’s quadrature components is called “squeezing.” By squeezing the uncertainty region, the squeezed area is generated. The term "squeezing" thus refers to a reduced quantum uncertainty. Due to the uncertainty principle, any optical measurement will have noise due to quantum fluctuations, but this limit can be beaten by using a “squeezed state.”

Squeezed states of light were theoretically predicted in 1976 by Horace P. Yuen in his paper entitled “Two-photon coherent states of the radiation field,” which was also selected as a milestone paper.

Use of squeezed states of light improved the sensitivity of the Laser Interferometer Gravitational-Wave Observatory (LIGO) in the mid-1980s, subsequently doubling its initial value.

Squeezing, or quantum noise reduction, has been mainly applied in the area of quantum optics. In 1991, we published Squeezed spin states, which was selected as a milestone paper this year. In this paper, we generalized the concept of spin squeezing, and presented formulas for experiments so that spin squeezing could be utilized in many fields. This has opened the way for applications of spin squeezing in measurement instruments such as interferometers.

As our paper wasn’t initially well understood by reviewers, we had to wait two and a half years until the paper was finally published.

I was aware that this paper was in the top 1% of most cited papers with over 1,000 citations. Being selected as a milestone paper from many papers in the past 50 years is an honor and encourages me in my work.

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