Quantum thermometry with trapped ions

Ding Fang, Wei-Bin Chen, Cheng-Hao Zhang +4 more

Wayne M. Itano, James C Bergquist, J. J. Bollinger +5 more

B. G. Norton, Erik W. Streed, M J Petrasiunas +2 more

We demonstrate millikelvin thermometry of laser-cooled trapped ions with high-resolution imaging. This equilibrium approach is independent of the cooling dynamics and has lower systematic error than Doppler thermometry, with ±5 mK accuracy and ±1 mK precision. We used it to observe the highly anisotropic dynamics of a single ion, finding temperatures of <60 mK and >15 K simultaneously along different directions. This thermometry technique can offer new insights into quantum systems sympathetically cooled by ions, including atoms, molecules, nanomechanical oscillators and electric circuits.

Yi Tao, Ting Chen, Hongyang Wang +5 more

In a trapped-ion system, accurate thermometry of ions is crucial for precisely evaluating the system state and performing quantum operations. However, when the motional state of a single ion is far away from the ground state, the spatial dimensionality of the phonon state sharply increases. Then it is difficult to realize accurate and mode-resolved thermometry with existing methods. In this work, we apply deep learning to the thermometry of a trapped ion and propose an efficient and mode-resolved method for accurately estimating large mean phonon numbers. We have also conducted experimental verification based on a self-developed surface trap. The result has shown the significant accuracy and efficiency of the method for thermometry of a single ion with large mean phonon numbers. The mode-resolved feature of our method makes it better applied to the characterization of system parameters, such as evaluating cooling effectiveness and analyzing surface trap noise. Our trained neural network model can be easily extended to other experimental setups and parameter ranges without modification of the experimental setups.

Robert B. Mann, Eduardo Martín-Martínez

Xie-Qian Li, Yi Tao, Ting Chen +4 more

Accurate thermometry of laser-cooled ions is crucial for the performance of the trapped-ion quantum computing platform. However, most existing methods face a computational exponential bottleneck. Recently, a thermometry method based on bichromatic driving was theoretically proposed by Vybornyi et al. [PRX Quantum 4, 040346 (2023)] to overcome this obstacle, which allows the computational complexity to remain constant with the increase of ion numbers. In this paper, we provide a detailed statistical analysis of this method and prove its robustness regarding several imperfect experimental conditions using Floquet theory. We then experimentally verify its good performance on a linear-segmented-surface-electrode-ion-trap platform. This method is proven to be effective from near the motional ground state to a few mean phonon numbers. Our theoretical analysis and experimental verification demonstrate that the scheme can accurately and efficiently measure the temperature in ion crystals.