Project Details
Projekt
Dilution refrigerator
Subject Area
Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
Term
Funded in 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 438873032
Today's interferometric gravitational wave detectors are already limited by quantum noise over a wide range of detection frequencies. Many table-top experiments in general quantum optics are also limited by quantum noise, where in particular quantum radiation pressure noise poses a fundamental limitation to measurement accuracy. In our "Quantum Control" group we are working on experimental realisations of methods to reduce quantum radiation pressure noise, both for potential use in future gravitational wave detectors and for applications in quantum optics in general (e.g. measurement of small forces). The most prominent method under investigation in our group called "Coherent Quantum Noise Cancellation" (CQNC) is being realised in our laboratories as an all-optical setup using micro-optomechanical oscillators as optomechanically coupled test masses. Here, the occurring quantum radiation pressure noise (caused by the optomechanical coupling of light and masses) is reduced by means of destructive interference with a tailored "anti-noise process" (consisting of a beam splitter interaction and a process of parametric downconversion). For use in our CQNC experiment the specifications of the employed oscillators have to be in a clearly defined parameter range: We require a very small mass (<50 ng), resonance frequencies in the range of 300 kHz to 500 kHz with moderate mechanical Q factors (around 1000), and a high (optical) reflectivity (for use as optomechanically coupled endmirrors in optical resonators). To this end we use photonic crystal membranes. Due to the stated boundary conditions, thermal noise dominates the movement (position uncertainty) of the oscillators at room temperature, making a measurement of quantum radiation pressure noise impossible. For any quantum noise reduction scheme (such as CQNC) it is therefore absolutely necessary to reduce the thermal noise by reducing the temperature of the oscillators such that the quantum radiation pressure noise becomes dominant and hence detectable. Only then can our experiment for quantum radiation pressure noise reduction produce measurable results. The temperatures that have to be reached are in the range of below 50 mK (better: 10 mK). These ultra-low temperatures can only be reached with a dilution refrigerator, as we are applying for here.CQNC is the first in a range of experiments on the topic of quantum noise reduction in optomechanical systems that we are investigating and planning on experimentally realising in our group. For all experiments it will be necessary to operate them at ultra-low temperatures, hence a mK-cryostat is required for all future work.
DFG Programme
Major Research Instrumentation
Major Instrumentation
Verdampfer-Kryostat
Instrumentation Group
8550 Spezielle Kryostaten (für tiefste Temperaturen)
Applicant Institution
Gottfried Wilhelm Leibniz Universität Hannover
