We show that, by using a feedback, the thermal noise in the axial oscillation, due to the back-action of the current of the external electronic device, can be squeezed up to 50%.
The hysteresis curve of the bistable cyclotron motion of a single electron in a magnetic field driven by external microwave radiation is obtained by only varying the phase of a phase-sensitive back-action-evading experimental setup. Thus the steady-state solution of the cyclotron motion includes two branches which could be switched by only changing the phase of the device. This effect is of particular interest as an example of the influence of the noise properties of the measurement apparatus on a microscopic system subjected to measurement.
With a superposition of static electric and magnetic fields, a Penning trap can confine a single electron indefinitely. A weak coupling of the electron to its environment makes the system ideal for precision measurements but renders detection of the electron’s motion difficult. In order to measure fundamental properties of an electron, we employ a Penning trap cooled by a dilution refrigerator. This experimental setup requires extremely low-noise and low-power cryogenic amplifiers for detection of the electron’s axial motion. We design and demonstrate new amplifiers, resulting in a significant decrease of the axial temperature and in an improved signal to noise ratio. We use feedback to cool the axial motion and to self-excite the axial motion for continuous monitoring of the axial frequency. These techniques for cooling and measuring the axial frequency may contribute to an improved measurement of the electron g factor, a more stringent CPT test in leptons, and a more precise measurement of the proton-electron mass ratio.
mechanical oscillator, and the collective electronic spin serves as the measurement device. By entangling the oscillator and collective spin and controlling the coherent dynamics via a many-body echo, a displacement is mapped into a spin rotation while avoiding quantum back-action and thermal noise. We achieve a sensitivity to displacements of 8.8 ± 0.4 decibels below the standard quantum limit and a sensitivity for measuring electric fields of 240 ± 10 nanovolts per meter in 1 second. Feasible improvements should enable the use of trapped ions in searches for dark matter.