Coupled quantized mechanical oscillators

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The harmonic oscillator is one of the simplest physical systems but also one of the most fundamental. It is ubiquitous in nature, often serving as an approximation for a more complicated system or as a building block in larger models. Realizations of harmonic oscillators in the quantum regime include electromagnetic fields in a cavity1,2,3 and the mechanical modes of a trapped atom4 or macroscopic solid5. Quantized interaction between two motional modes of an individual trapped ion has been achieved by coupling through optical fields6, and entangled motion of two ions in separate locations has been accomplished indirectly through their internal states7. However, direct controllable coupling between quantized mechanical oscillators held in separate locations has not been realized previously. Here we implement such coupling through the mutual Coulomb interaction of two ions held in trapping potentials separated by 40 μm (similar work is reported in a related paper8). By tuning the confining wells into resonance, energy is exchanged between the ions at the quantum level, establishing that direct coherent motional coupling is possible for separately trapped ions. The system demonstrates a building block for quantum information processing and quantum simulation. More broadly, this work is a natural precursor to experiments in hybrid quantum systems, such as coupling a trapped ion to a quantized macroscopic mechanical or electrical oscillator9,10,11,12,13.

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Figure 1: Micrograph of the ion trap, showing radio-frequency (RF) and d.c. electrodes, and gaps between electrodes (darker areas).
Figure 2: Motional spectroscopy of two coupled ions near the avoided crossing.
Figure 3: Energy swapping between two ions in separate trapping potentials at the level of a few quanta.
Figure 4: Motional exchange between two ions in separate trapping potentials at approximately the single-quantum level.


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This work was supported by IARPA, DARPA, ONR and the NIST Quantum Information Program. We thank M. Biercuk, A. VanDevender, J. Amini, and R. B. Blakestad for their help in assembling parts of the experiment, and we thank U. Warring and R. Simmonds for comments. This paper, a submission of NIST, is not subject to US copyright.

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K.R.B. and C.O. participated in the design of the experiment and built the experimental apparatus. K.R.B. collected data, analysed results and wrote the manuscript. Y.C. fabricated the ion trap chip and collected data. A.C.W. maintained laser systems and collected data. D.L. participated in the design of the experiment, collected data and maintained laser systems. D.J.W. participated in the design and analysis of the experiment. All authors discussed the results and the text of the manuscript.

Correspondence to K. R. Brown.

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Brown, K., Ospelkaus, C., Colombe, Y. et al. Coupled quantized mechanical oscillators. Nature 471, 196–199 (2011) doi:10.1038/nature09721

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