Figure 1: Level scheme and Ramsey interference.
(a) The main figure shows the photothermal ionization spectrum (PTIS—black trace) of the Rydberg transitions for Si:P. Top left inset: the Rydberg state energies below the ionization threshold with the transition frequency for 1s(A1)→2p± transition shown in THz (blue arrow), along with the phonon energy required for ionization of the excited state (red arrow). Top right inset: schematic of the potential for the phosphorous impurity in Si under external bias, along with the 1s and 2p wavefunctions. The curly red line represents the incoming photon that leaves atoms excited in the 2p± state, and phonons collapse (dashed blue line) the wavefunction. A (small) fraction is ionized that is proportional to the probability for the excited state, and the ionization is detected in the conductivity. (b) The Ramsey sequence showing constructive interference (with π/4 pulses by way of example for consistency with d). The pulse sequence is shown at the top, and the y-component of the Bloch vector (laboratory frame), proportional to the polarization, is at bottom. (c) Same as for b for an extra half cycle delay and consequent destructive interference. (d) A Ramsey sequence followed by a rephasing pulse for optical echo read-out.
