Multiple Packets of Neutral Molecules Revolving for over a Mile

The level of control that one has over neutral molecules in beams dictates their possible applications. Here we experimentally demonstrate that state-selected, neutral molecules can be kept together in a few mm long packet for a distance of over one mile. This is accomplished in a circular arrangement of 40 straight electrostatic hexapoles through which the molecules propagate over 1000 times. Up to 19 packets of molecules have simultaneously been stored in this ring structure. This brings the realization of a molecular low-energy collider within reach.

Figure 1

Upper panel: Photograph of the 0.5 m diameter molecular synchrotron with a zoom-in of three hexapoles. Middle panel, left: Voltage configuration used to transversely confine neutral molecules, overlayed with a contour plot of the resulting electric field strength. Right: Electric field strength (both for confinement and bunching) as a function of position along the equilibrium orbit. Lower panel: Scheme of the time dependence of the voltage difference between adjacent hexapole electrodes during operation of the synchrotron. By temporarily switching to a higher voltage-difference whenever the packet passes through a gap, ammonia molecules with a velocity spread of one $\mathrm{m}/\mathrm{s}$ are kept in a tight bunch while revolving. The green dashed curve indicates the equilibrium orbit of ${\mathrm{ND}}_3$ molecules with a forward velocity of $125\mathrm{m}/\mathrm{s}$.

Figure 2

Measurements of the density of ${\mathrm{ND}}_3$ molecules as a function of time (in seconds) for a selected number of round trips. The observed temporal width of $21\mu \mathrm{s}$ after 1025 round trips corresponds to a packet length of 2.6 mm after a flight distance of more than a mile. The inset shows the exponential decay of the signal with time.

Figure 3

Time-of-flight measurement showing 19 packets of ammonia molecules revolving simultaneously in the molecular synchrotron. The horizontal axis shows the time relative to the time at which the first injected packet has completed 150 round trips. Each packet is labeled with two numbers: the main number labels the order of injection whereas the subscript labels the number of completed round trips.