Seminars

# Classification, Generation, and Application of Spin Squeezing

## by Emi Yukawa (RIKEN CEMS)

Asia/Tokyo
Room 433, Main Research Building (RIKEN Wako)

### Room 433, Main Research Building

#### RIKEN Wako

Description
Date: June 13 (Tue) Time: 13:30 - Place: Main Research bldg. 433 Speaker: Emi Yukawa (RIKEN CEMS) Title: Classification, Generation, and Application of Spin Squeezing Abstract: Squeezed states have been intensively investigated originally in optics and extended to various bosonic and spin systems. A defining feature of squeezing is to enhance the quantum nature such as reduced quantum noise and macroscopic entanglement, which form the basis of their applications to precision measurements, for instance, the gravitational wave detector LIGO [1] and subdiffraction-limited quantum imaging within a living cell [2]. Squeezed spin states (SSSs) [3] are sensitive to magnetic field rather than photon number or phase, so they have been considered to be applicable to high precision and non-destructive magnetometers. By utilizing such macroscopic and highly entangled states of $N$ spin-$1/2$ particles in precision measurements, the measurement precision improves by a factor of $N^{1/2}$ compared to the standard quantum limit (SQL) at most, which is the ultimate limit of the precision called the Heisenberg limit. It remains still challenging to implement SSSs feasible for high-resolution magnetometers, i.e., SSSs of solid state spins; however, they have been observed in ensembles of pseudo spin-$1/2$ cold atoms and recently extended to cold atoms of higher spins. The spin squeezing of spin-$1/2$ particles is well understood: The spin ensemble obeys the su($2$) algebraic structure and consequently the observables whose quantum fluctuations can be reduced are the magnetizations. In the case of the ensembles of spin-$J$ particles, which features the su($2J+1$) ($J>1/2$) algebraic structure, they show a rich variety of squeezing in addition to the well know squeezing among magnetization observables. In view of current and near future experiment developments, it is important to characterize the rich structure of squeezing in the ensembles of spin-$J$ particles. We address the questions of what observables and to what extent we can squeeze beyond the SQL in the ensembles of spin-$J$ particles based on the Lie algebra [4]. In the presentation, we also propose how to implement spin squeezing in solid spin systems [5] and generation of other macroscopically entangled states via the spin squeezing Hamiltonians [6]. [1] H. Aasi et al., Nature Photonics 7, 613 (2013). [2] M. A. Taylor et al., Phys. Rev. X 4, 011017 (2014). [3] M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138 (1993). [4] E. Yukawa, M. Ueda, and K. Nemoto, Phys. Rev. A 88, 033629 (2013); E. Yukawa and K. Nemoto, J. Phys. A 49, 255301 (2016). [5] S. Dooley, E. Yukawa, Y. Matsuzaki, G. C. Knee, W. J. Munro, and K. Nemoto, New J. Phys. 18, 053011 (2016). [6] E. Yukawa, G. J. Milburn, and K. Nemoto, arXiv:1703.05666 (2017). QHP seminars
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