Research project is (co) funded by the Slovenian Research Agency.
UL Member: Faculty of Mathematics and Physics
Code: N1-0180
Project: Quantum optomechanics with optically trapped sub-micron particles
Period: 1. 3. 2021 - 29. 2. 2024
Range per year: 0,7 FTE category: C
Head: Rainer Kaltenbaek
Research activity: Natural sciences and mathematics
Research Organisations, researchers, citations for bibliographic records
Project description:
By using the pressure light can exhibit on objects, it is possible to influence even the motion of macroscopic objects. Well-known examples are the tails of comets due to solar radiation pressure and the noticeable effects of solar radiation pressure on spacecrafts. This interaction between light and the motion of objects can be used to cool the centre-of-mass motion of macroscopic objects close to the absolute minimum allowed by the laws of quantum physics. Once macroscopic objects are cooled into this “quantum regime”, they promise to be useful tools for applications in quantum communication, quantum sensing, and for tests of the foundations of physics. This field of physics is called “quantum optomechanics” and has drawn significant attention since the mid 2000s. A very promising platform for such experiments is to use optically trapped sub-micron test particles. Using optical trapping promises to allow a better isolation of the trapped particles from negative influences of their environment like, e.g., vibrations, compared to clamped optomechanical systems. One of the strongest remaining interactions with the environment are collisions between the test particle and the surrounding gas. For that reason, it is essential to optically trap the test particles in ultra-high vacuum, but loading test particles into optical traps and stably trapping them in vacuum remains a challenge. To address this challenge, we will first trap test particles in moderate vacuum and then transfer them into a vacuum chamber by passing the particles through a hollow-core photonic crystal fibre. This is an optical glass fibre with a thin, hollow core in its centre through which we can transport the test particles using an optical conveyor belt from a “loading chamber” at moderate vacuum to a “science chamber” at ultra-high vacuum. While the particle moves along the fibre, we will have to modulate the intensity of the guiding beams in order to cool the particle’s radial motion. We will do that by monitoring the particle’s position and then lowering or increasing the trap depth accordingly. This is called “feedback cooling”. Once a test particle is in our optical trap in the “science chamber”, we will again use feedback cooling to keep the particle stably trapped. At higher pressures, the surrounding gas would ensure that the particle remains in its trap, but at ultra-high vacuum levels we have to dampen the particle motion. While this can be achieved via feedback cooling, getting the trapped particles into the quantum regime requires additional cooling power. For that purpose, we will place our optical trap between two highly reflective mirrors. These mirrors will form a high-finesse “optical cavity” in which light of the proper wavelength can travel back and forth many times before eventually leaving the cavity. In this case, the light is said to be “on resonance” with the cavity. If the light we use for optically trapping the test particle has a slightly longer wavelength than what is needed to be on resonance with the cavity, the light will “borrow” energy from the motion of the trapped particle to be on resonance. This can provide additional cooling of the particle’s centre-of-mass motion. Very recently it was shown by the project leader’s former colleagues in Vienna that this approach allows cooling the motion of optically trapped particles into the quantum regime. Our goal will be to set up a state-of-the-art system to cool optically trapped sub-micron particles into or close to the quantum regime by using a simpler approach than the one in Vienna. Instead of driving the optical trap and the cavity at different cavity resonances, we will operate the optical trap close to the wavelength used to driving the cavity. Our work will kick start the field of quantum optomechanics in Slovenia, providing opportunities to contribute to state-of-the-art research in quantum optics, quantum sensing, quantum computation and tests of the foundations of quantum physics.
