In this project, we are studying the interaction between optical fields and the mechanical motion of a levitated nano-object. Our aim is to prepare and study non-Gaussian quantum states of motion (i.e., with negative values in the Wigner function) of large objects to test the validity of quantum mechanics at unprecedented large scales.

A cavity-mediated interaction provides a link between the quantum and the macroscopic worlds.

Ion-assisted levitated quantum optomechanics

Typically, levitated cavity optomechanical systems consist of a single dielectric object confined using an electromagnetic field, e.g., using optical tweezers or a quadrupole trap, in which the object oscillates periodically around its equilibrium position. The motion of such an object can then be coupled to the field of an optical cavity: if the object is much smaller than the wavelength of light in the cavity, then the effective cavity length depends on the object's position along the cavity standing wave. This dispersive coupling makes it possible to implement optomechanical protocols such as motional readout, resolved sideband cooling, and — once the object has been cooled to the motional ground state — entanglement with the cavity field.

Both a nanosphere and an ion are coupled to an optical cavity.

 Despite its similarity to the field of cavity QED, cavity optomechanics does not require the presence of an electronic transition. Therefore, mesoscopic oscillators can in principle be used to prepare mechanical quantum states such as center-of-mass superpositions. However, coupling a levitated nanosphere to a macroscopic Fabry-Perot resonator leads to very small single-photon optomechanical coupling rates g 0 which, for realistic parameters, are smaller than the cavity photon lifetime κ-1. Thus, these optomechanical systems typically operate in the so-called linearized regime, in which the mechanical oscillator's steady state is always characterized by a positive Wigner function.

To overcome these limitations, we follow a new approach to extend the field of levitated optomechanics to multiple objects, more specifically, to a single ion and a silica nanosphere. Both species will be confined using an on-chip linear quadrupole trap driven by two frequencies, with the cavity field aligned along the trap axis. We are planning to use a linear trap with an axis length of 300 μm, making our levitation scheme compatible with a range of cavity lengths, from 400 μm on up.

This configuration will allow us to implement a hybrid system where both the ion's internal energy levels and the levitated nanosphere's center-of-mass motion couple to the cavity field. Then the optical field can be used to mediate an interaction between the two systems, enabling passive ground-state cooling schemes outside the resolved sideband regime and the preparation of non-classical motional states of the nanosphere. Additionally, our system will allow us to study collective dynamics with multiple levitated nanoparticles, where several mechanical modes can be simultaneously coupled to the cavity field.

Project Members

Dmitry Bykov, Lorenzo Dania, Matthias Knoll, Tracy Northup

Former members: Pau Mestres, Lisa Schmöger


Funding for this project is provided by the Austrian Science Fund through the START Program (Project Y 951).

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