Advanced LIGO Quantum noise everywhere Radiation pressure noise Stronger measurement  larger backaction Shot noise More laser power  stronger measurement This slide shows the noise limits expected for Advanced LIGO (construction begins in early 2011). The EM vacuum fluctuations entering the output port of the beam splitter are the limiting noise at all frequencies shown. Phase quadrature fluctuations give rise to the shot noise limit, and amplitude quadrature to the radiation pressure noise. Where the SN and RPN contributions are equal, Advanced LIGO will operate at the standard quantum limit (SQL). It is this limit that has prompted us to ask the questions: Can we manipulate the quantum noise to design more sensitive gravitational wave (GW) detectors? Can we design experiments to test these ideas for better GW detectors and also explore open questions in quantum mechanics on macroscopic scales? The answer to both these questions is YES. The next two slides give examples…

Classical radiation pressure effects Stiffer than diamond 6.9 mK Stable OS Radiation pressure dynamics Optical cooling This slide summarizes the results of an experiment involving a 1 gram mirror oscillator that is optically cooled and trapped . This laser cooling technique is an important tool for being able to enter the quantum regime with such large mechanical systems. The bottom picture is a schematic of the experiment. Two laser beams that are resonant at different frequencies and detunings of the optical cavity are used to optically trap and cool the 1 gram end mirror. The top left shows the trapping – the frequency response of the driven oscillator show the resonant frequency shifting higher as the laser power is increased to make a stiffer and stiffer trap. The mechanical resonance frequency of the oscillator was 172 Hz, and was shifted to 5 kHz by the optical trap. This corresponds to a stiffness of 2e6 N/m, 20% stiffer than if the optical mode of the cavity (1mm diameter, 1 m long) were made of diamond. The top right figure shows the spectral density of displacement of the optically trapped oscillation mode. As the optical damping is increased, the oscillation mode of the 1 gram mirror along the cavity axis is cooled to 7 mK (the entire experiment is carried out at room temperature). 10% 90% 5 W ~0.1 to 1 m Corbitt et al. PRL (2007)

LIGO Quantumness N = 234 SQL LSC, New J. Phys. (2009) This shows a similar experiment performed on the Initial LIGO detectors that were operated between 2005 and 2007. Here we use active feedback cooling and trapping to cool the 10 kg gram mirrors of LIGO to 1.4 microKelvin, which corresponds to 234 quanta in the oscillation mode (top left figure, showing displacement spectral density around the trapped/cooled mode). The top right shows curves for Initial LIGO (blue – design, yellow – data), Enhanced LIGO (red) and Advanced LIGO (purple). Advanced LIGO will be at the SQL, and hence the quantum ground state of the 40 kg mirror oscillator. LSC, New J. Phys. (2009)