Noise-insensitive temperature quantum measurement
Among the difficulties we have to face while measuring a physical quantity, there is the isolation of the measurement from background noise, without losing sensitivity. In order to solve this problem, INRiM quantum optics group and University of Turin developed a thermometry protocol that is weakly affected by noise, as a part of the european project Pathos. The protocol is an innovative technique based on quantum sensing, a new research field dedicated to the design of sensors that can improve measurement capabilities by exploiting specific properties of quantum systems.
The technique, described in a study published on Physical Review Applied, exploits the properties of a particular defect in diamond structure, the nitrogen-vacancy complex. In the crystal lattice of carbon atoms constituting the diamond structure, one of the atoms is missing and there is a substitutional nitrogen located nearby. Due to the presence of this defect, when radiated by a green light, the diamond itself emits light radiation.
The intensity of this light radiation can be controlled by applying an electromagnetic field in microwave frequencies. For a specific frequency, the emitted radiation becomes suddenly less intense: this is the so-called resonant frequency, which is influenced by temperature variations. In the laboratory, temperature measurements are performed by monitoring a temperature-dependent shift in the resonant frequency of nitrogen-vacancy complex.
The method developed by INRiM researchers overcomes the limits of precedent techniques. Applying a magnetic field with right intensity and direction to a diamond sample with a nitrogen-vacancy complex, it is possible to amplify the difference between the minimum peak of light intensity emitted by the diamond and the maximum one, obtaining a measurement very sensitive to temperature variations. Moreover, the technique allows “protecting” the measure from the magnetic noise deriving from the equipment or Earth's magnetic field.
In perspective, this technique could allow a sensitivity improvement of one order of magnitude with respect to previous analogous methods, offering more accurate measurements for applications in fields ranging from nanotechnology to biophysics.