Atom Interferometry with up to 24-Photon-Momentum-Transfer Beam Splitters

We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Bordé (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom’s internal state is not changed, important systematic effects can cancel.

Figure 1

(a) MZI. “$\pi /2$” pulses transfer momentum with a probability of $1/2$. They thus act as beam splitters; “$\pi$” pulses act as mirrors. (b) Conjugate RBIs; either is selected by the last $\pi /2$ pulse pair as described in the text. Not shown are outputs of the third beam splitter which do not interfere.

Figure 2

Setup (simplified). PD; photodetector. For the injection lock, we use polarization spectroscopy [26], which does not require modulation of the laser light. AOM1 (Isomet 1206C) amplitude modulates, AOM2 (Crystal Technology 3200-124) splits and AOM3 (Isomet 1205C-1) ramps the frequency of the beams. EOM2 (New Focus) generates $\sim 9.2\mathrm{GHz}$ sidebands for the velocity selection.

Figure 3

(a)–(d) show MZ fringes with between 12 and $20\hslash k$ momentum transfer; (E and F) are RB fringes with 12 and $24\hslash k$. (G and H) show a conjugate $20\hslash k$ RB-pair. Throughout, $T=1\mathrm{ms}$, $T^{\prime }=2\mathrm{ms}$. Each data point is from a single launch (that takes 2 s), except for F, where 5-point adjacent averaging was used. The lines represent a sinewave fit.

Figure 4

Left: $C$ and $V$ (MZ) of $12\hslash k$ MZIs. $V$ (RB) shows larger visibility at longer times for a RBI with vibration isolation (Minus K Technology Model 40BM1) for the lower beam and beat optics (Fig. 2). Right: Visibility versus momentum transfer.