Quantum state purity versus average phonon number for characterization of mechanical oscillators in cavity optomechanics
| Autor: | Kjetil Børkje, Francesco Marin |
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| Rok vydání: | 2023 |
| Předmět: | |
| Zdroj: | Physical Review A. 107 |
| ISSN: | 2469-9934 2469-9926 |
| Popis: | Quantum oscillators in Gaussian states are often characterized by average occupation numbers that refer to a basis of eigenstates of the non-interacting oscillator Hamiltonian. We argue that quantum state purity is a more appropriate characteristic of such states, which can be applied to oscillators of any dimensionality. For a one-dimensional oscillator, the state purity is directly related to a thermal occupation number defined with respect to the number state basis in which the oscillator's quantum state is thermal. Thus, it naturally introduces a more versatile definition of an average occupation number. We study optomechanical sideband cooling of one- and two-dimensional mechanical oscillators in particular, and derive exact analytical expressions for the maximal mechanical state purity achievable in the quantum backaction limit. In the case of a one-dimensional oscillator, we show that the thermal occupation number related to purity can be well approximated by the average phonon number in the weak-coupling regime, but that the two differ in the regime of ultrastrong optomechanical coupling or in cases where the oscillator's resonance frequency is strongly renormalized. 13 pages, 4 figures |
| Databáze: | OpenAIRE |
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