Sympathetic cooling of a membrane oscillator in a hybrid mechanical–atomic system

Journal name:
Nature Nanotechnology
Volume:
10,
Pages:
55–59
Year published:
DOI:
doi:10.1038/nnano.2014.278
Received
Accepted
Published online

Sympathetic cooling with ultracold atoms1 and atomic ions2 enables ultralow temperatures in systems where direct laser or evaporative cooling is not possible. It has so far been limited to the cooling of other microscopic particles, with masses up to 90 times larger than that of the coolant atom3. Here, we use ultracold atoms to sympathetically cool the vibrations of a Si3N4 nanomembrane4, 5, the mass of which exceeds that of the atomic ensemble by a factor of 1010. The coupling of atomic and membrane vibrations is mediated by laser light over a macroscopic distance6, 7 and is enhanced by placing the membrane in an optical cavity8. We observe cooling of the membrane vibrations from room temperature to 650 ± 230 mK, exploiting the large atom–membrane cooperativity9 of our hybrid optomechanical system10, 11. With technical improvements, our scheme could provide ground-state cooling and quantum control of low-frequency oscillators such as nanomembranes or levitated nanoparticles12, 13, in a regime where purely optomechanical techniques cannot reach the ground state8, 9.

At a glance

Figures

  1. Coupling mechanism and schematic of the experiment.
    Figure 1: Coupling mechanism and schematic of the experiment.

    a, A thin dielectric membrane is placed inside a Fabry–Perot cavity near the slope of the intracavity intensity standing wave. Mirror reflectivities R2 ≈ 1 and R1 < R2 ensure that the driving laser is reflected and forms an optical lattice for a cloud of ultracold atoms. The light couples the membrane vibrations xm to the atomic motion xa. The membrane motion is independently read out with a detection beam. b, The membrane–cavity system and the laser-cooled atoms reside in separate vacuum chambers (grey boxes). PBS, polarizing beamsplitter; EOM, electro-optic modulator; OC, optical circulator; PD, photodiode. c, Optical transmission spectrum of the cavity showing the cavity resonance frequency ωc as a function of membrane position xm. The fundamental TEM00 cavity mode (strong signal) and the TEM20 mode (weak signal) can be identified. At the crossing points, the transmission through both modes adds up on the photodiode. We operate on the TEM00 mode at the point where the slope G = −dωc/dxm is largest. In our single-sided cavity there are two points of maximal |G| with either low or high . d, Mechanical displacement spectra of the membrane fundamental mode for different lattice laser powers P0 and laser-cavity detuning Δ < 0, without atoms in the lattice.

  2. Sympathetic cooling of the membrane.
    Figure 2: Sympathetic cooling of the membrane.

    a,b, Membrane fundamental mode temperature T as a function of time in a three-step sequence: A, atoms not resonant (P0 = 5.5 mW); B, atoms resonant (P0 = 16.5 mW); C, P0 = 16.5 mW but atomic laser cooling switched off. Red curves are recorded with atoms in the lattice, blue curves without atoms. Dark blue curve: detection beam only. Dashed lines: measurement noise floor and room temperature. Measurements were taken with a spectrum analyser set to a fixed frequency ≈Ωm with bandwidth BW ≫ Γtot, and averaged over 20 experimental runs. a, Measurement with , Δ = −0.013 ± 0.005 κ and BW = 2π × 0.5 kHz. b, Measurement with , Δ = −0.022 ± 0.002 κ and BW = 2π × 2 kHz.

  3. Resonant turn on of sympathetic cooling.
    Figure 3: Resonant turn on of sympathetic cooling.

    a, Membrane fundamental mode temperature as a function of laser power P0, with atoms in the lattice (Tsym) and without atoms (Topt). Blue line: fit with a theory of cavity optomechanical cooling with laser noise, but without atoms. Measurements were performed with , Δ = –0.032 ± 0.005 κ and averaged over 20 runs. The standard error of the mean (s.e.m.) is shown. The membrane was at a position where G = 0.92max(G), decreasing gN by the same prefactor. Inset: membrane displacement spectra corresponding to the big points in the main plot. The spectra are distorted because of fluctuations in Δ due to a jitter in the membrane position. b, Sympathetic cooling rate Γsym obtained from the data in a as a function of atomic frequency in the lattice centre, Ωa(0). Error bars are calculated from the s.e.m. by error propagation. Red line: model of Γsym taking the lattice laser profile into account. Shaded red region indicates ±10% uncertainty in Ωa(0).

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Affiliations

  1. Departement Physik, Universität Basel, CH-4056 Basel, Switzerland

    • Andreas Jöckel,
    • Aline Faber,
    • Tobias Kampschulte,
    • Maria Korppi,
    • Matthew T. Rakher &
    • Philipp Treutlein

Contributions

P.T. conceived and supervised the study. A.J., M.K., A.F., T.K. and M.T.R. built the experimental set-up. A.J., A.F. and T.K. performed the experiments and analysed the data, with frequent discussions with P.T. All authors discussed the results and contributed to the manuscript.

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The authors declare no competing financial interests.

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