Widely Tunable Coupling between a Mechanical Mode and Cavity Photons via a Superconductor
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Widely Tunable Coupling between a Mechanical Mode and Cavity Photons via a Superconductor Joonho Jang∗ Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University, Seoul 08826, Korea and Center for Correlated Electron Systems, Institute for Basic Science, Seoul 08826, Korea (Received 7 October 2020; revised 14 October 2020; accepted 15 October 2020) Inducing strong coupling between a mechanical degree of freedom and optical modes has been of great scientific interest itself, but also important for the applications to the quantum information technology. However, photons and mechanical modes usually are weakly interacting due to very small momentum exerted by photons. Here, we demonstrate a scheme for coupling a resonance mode of a mechanical oscillator with an optical cavity, by utilizing the magneto-optical effect of a mesoscopic superconductor attached to the mechanical oscillator. The absorption of cavity photons by the superconductor in external magnetic fields gives rise to a retarded force that modifies the damping and frequency of the oscillator. Measurements using NbSe2 achieved approximately a factor of 17 reduction in the mode temperature from 5.0 K to 260 mK. Keywords: Optomechanics, Mechanical oscillator, Superconductor DOI: 10.3938/jkps.77.927
I. INTRODUCTION Besides pure scientific interest to observe macroscopic quantum mechanical effect [1–3] and to increase detection sensitivity on displacement and/or weak forces [4], achieving a small occupation number in a mode of a mechanical oscillator is an important step in realizing high fidelity qubit operations [5]. Gigahertz oscillators are able to achieve the quantum ground state at cryogenics temperatures, but have usually high dissipation to limit the coherence time of phonon states. On the other hand, even at cryogenic temperatures sub-gigahertz mechanical oscillators have a significant thermally exited occupation number. As a solution, various passive [6–8] and active [9–12] cooling schemes were proposed and experimented to artificially minimize the occupation number. Also, recent progress on realizing the strong coupling regime between a mechanical mode and photon fields in optomechanical and electromechanical devices suggest that the ground state cooling is within reach [13]. Using the field-matter interaction, parametrically coupled systems of a photonic cavity and a mechanical oscillator have been successful in attaining low phonon occupation in a single vibrational mode of the mechanical oscillator [14]. Achieving strong coupling between the cavity photons and the mechanical mode, however, is challenging and limits the efficiency of the cooling for reaching the quantum ground state. In the present pa∗ E-mail:
[email protected]
pISSN:0374-4884/eISSN:1976-8524
per, using tunable coupling strength of a superconductor with external magnetic fields and photons in a detuned optical cavity, cooling of a mode temperature of a mechanical oscillator from 5K to 180mK are presented.
II. EXPERIMENT A basic setup of exper
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