1. RF sensing based on NV
NV spin can be used as a detector for AC fields. Utilizing the optical spin-initialization 80 − 95 % and spin-dependent optical contrast of ∼ 30 − 40 % allows to drive and readout Rabi-oscillations and, hence, determine the strength of the B-field from a target RF source. The underlying analysis is based on recording Rabi-Oscillations over time (requiring at least one full oscillation within the observable time-span) and then measuring near the π/2-time of the driving signal.
2. RF power sensing based on NV
RF power transmitted through an RF waveguide can be measured using NV centre RF sensors placed in the interior of the waveguide to record the RF B-field amplitude. For practical implementations, small diamond crystals (small compared to the RF wavelength, as realised, e.g., with micron sized diamond platelet) could be integrated into the waveguide. The required optical-interface to the NV is realized, e.g., via a hole with ∼ 500 nm diameter in the waveguide wall. The best sensitivities are reached for an operation point close to T (ρ 1) and weaker RF powers.
3. Local imaging of RF fields based on scanning NV microscopy
Due to its stability in the diamond lattice, the NV center can spatially resolve the RF magnetic fields in a device under test (DUT) by means of scanning the diamond across its surface and performing RF sensing. Large magnetic fields B(ext) may need to be applied to the DUT and the microscope employed, but DUTs with operating frequencies of up to 280 GHz could be studied. The ideal setup favours the use of NV sensors with spins that are oriented along the plane of the DUT. The introduction of a RF nearfield antenna to manipulate the sensor-spin independent to the DUT is an optional addition that may help to refine the microscope’s operation or mitigate the field-requirement issues.
The main points to track during development of this technique are the field requirements (perpendicular fields < 10mT w.r.t. NV sensor orientation) and the susceptibilities of the DUT and setup-components to large magnetic fields. Another important aspect is the realization of the scanning functionality as it requires relative precise movement of the DUT relative to the sensor and its readout. Additionally, in order to achieve a high spatial resolution the lateral drifts during a measurement have to be minimized and accounted for.
4. Rydberg-based detection of AC electrical fields
The detection of AC electric fields with Rydberg atoms is a very sensitive detection method for electrical fields. By using additional electric or magnetic fields, the resonance frequency can furthermore be tuned such that a quasi continuous spectrum of frequencies can be probed.
5. Coplanar waveguide in a vapour cell
Rydberg atoms as probes for electric fields also offer a very large dynamic range. Electric field strength as small as 46µV/m and as large as 5 kV/m have been measured using essentially the same technique. To bring the Rydberg atoms into the electric field to be measured and mitigate the problem of interference at the glass, the evanescent field close to a coplanar waveguide (CPW) placed inside the vapour cell can be measured. CPWs allow to guide many different frequencies and their electric field distribution can be accurately simulated.
6. Rydberg sensor based vector network analyzer
Such sensors would measure power and phase of the electric field at two or more ports of a device under test.
7. Single Rydberg atom as a scanning probe for high frequency electric fields
Single neutral atoms can be trapped in a so called optical tweezer - the focus of an off resonant laser beam [50]. These atoms can be coherently excited into a Rydberg state, which constitutes a highly localized probe for electric fields. the outstanding control and measurement capabilities can be also very useful for metrological tasks. To this end one could consider a single or even a few trapped Rydberg atoms, which are spatially scanned in the vicinity of a device under test. This would allow a probe for the spatial electric field distribution.
