Fig. 5
Design of sensing sequences. a Four sensing steps with DqMA used to create different sensing tasks. Every sensing step starts with the sensor spin prepared in an eigenstate and the memory spin in a superposition state. These sensing steps have two tasks: accumulate a phase on one of the components of the memory spin (i.e., ϕ 0 or ϕ 1), and either flip or keep the sensor-spin state (i.e., \(\left| {{s_f}} \right\rangle = \left| {{s_i} \oplus 1} \right\rangle\) or \(\left| {{s_f}} \right\rangle = \left| {{s_i}} \right\rangle\)). b Refinement of a single Ramsey-type sensing step into an echo-type sequence comprising two sensing steps and an intermediate flip of target spins to facilitate assignment. Flips can be selective, by turning on the hyperfine gradient during the pulse (lower part). c Sensing sequences used in Figs. 2–4. Optional elements are marked with a blue star. The optional π/2 pulses on the memory spin convert quantum into classical storage and vice versa. The optional laser pulse sequences realize different decoupling methods. The outer short π pulses on the 13C spins filter the accumulated signal in a broad spectral range of NMR frequencies, whereas the central, longer-lasting π pulse provides high-frequency resolution. The lower part illustration the spectral filters for 13C target spins from the above sequence. The overall signal results from target spins that are flipped by all three pulses. d Noise filter functions of the used detection sequences acting on sensor and memory, in comparison to commonly known detection schemes acting only on the sensor (spin echo (SE), periodic dynamical decoupling (PDD)). On the left, the sensing steps as shown in (a) are used for encoding and decoding, whereas the right graph incorporates the echo-type sequence, shown in (b)
