HOM sequence, SA side

Once a single $^{87}$Rb atom is loaded from a magneto-optical trap (MOT) into the tightly focused far-off-resonant optical dipole trap (FORT) at 980nm, a measurement sequence is initiated. The main steps are: (1) 10ms of molasses cooling using the MOT beams, with the MOT quadrupole magnetic field turned off; (2) switching off the MOT beams and applying a bias magnetic field of $\approx\,$2$\,$G along the quantization axis; (3) 10ms of optical pumping, during which a pump beam tuned to $5S_{1/2}\ket{F=2} \rightarrow 5P_{3/2}\ket{F=2}$, and a repump beam tuned to $5S_{1/2}\ket{F=1} \rightarrow 5P_{1/2}\ket{F=2}$, both $\sigma -$ polarized, prepare the atom in $5S_{1/2}\ket{F=2,m_F=-2}$; (4) 100ms excitation window, during which a trigger signal from the FWM setup triggers an excitation pulse to the atom; (5) Steps 3 and 4 are repeated four times; (6) using the MOT beams, check if the atom is still in the FORT by monitoring fluoresence with detector $D_L$; if `yes', start a new measurement sequence; otherwise discard the data collected in this sequence, turn on the MOT, and wait for another atom to be loaded into the FORT.

Pulse generation

The excitation pulse is a 3ns $\pi$ pulse resonant with $5S_{1/2}\ket{F=2,m_F=-2} \rightarrow 5P_{3/2}\ket{F=3,m_F=-3}$, 
%The excitation probability is $\approx\,$0.8, and 2\% of the spontaneously emitted photons are collected and sent to the HOM interferometer. 
generated using two electro-optic intensity modulators (EOMs) in series. An acousto-optic modulator (AOM) used for frequency tuning also acts as an additional optical switch. This configuration increases the effective extinction ratio and minimizes leakage of resonant light that can interact with the atom.  When a trigger signal arrives from the FWM setup, the AOM is turned on after a variable delay $\Delta t_d$. The excitation pulses are generated 850ns later when the AOM output has stabilized, then the AOM is turned off. $\Delta t_d$ is adjusted to obtain the desired delay between the SA and FWM photon at the HOM beamsplitter.

Choice of pulse parameters


G2
