Quantum tricks with gravitational-wave detector mirrors
LIGO researchers tune motion of suspended interferometer mirrors to cool a 10-kg optomechanical oscillator to near its motional ground state
In the last few decades, physicists have devised new ways to cool objects close to absolute zero. At these low temperatures their atoms are near their quantum motional ground state. So far, this has been achieved only for small objects with masses in the nanogram range. Now members of an international team have managed to cool a human-scale “pseudo object” with a mass of 10 kilograms to close to its motional ground state. The pseudo object is the combined motion of four widely separated objects. The researchers controlled the relative motion of the four 40-kilogram test masses in the two arms of a LIGO detector such that they could observe this oscillator at an effective temperature of just 77 nanokelvin.
The motion of a mechanical object, even a human-sized object, should be governed by the rules of quantum mechanics. Coaxing them into a quantum state is, however, difficult because the thermal environment masks any quantum signature of the object’s motion. The thermal environment also masks the effects of proposed modifications of quantum mechanics at large mass scales. We prepared the center-of-mass motion of a 10-kilogram mechanical oscillator in a state with an average phonon occupation of 10.8. The reduction in temperature, from room temperature to 77 nanokelvin, is commensurate with an 11 orders-of-magnitude suppression of quantum back-action by feedback and a 13 orders-of-magnitude increase in the mass of an object prepared close to its motional ground state. Our approach will enable the possibility of probing gravity on massive quantum systems.