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We have designed a new type of neutron interferometer, which will be less sensitive to slow vibrations.
Single crystal neutron interferometers are extremely sensitive to environmental noise, including vibrations. Sensitivity is a result of 1) many wavelengths combined in interferometer, 2) slow velocities of neutrons, 3) long measurements times. Most neutron interferometers require vibration isolation, which is usually a big and massive system (especially for low frequency vibrations). We have designed a new type of neutron interferometer, which will be less sensitive to slow vibrations. Not only will this design improve the interferometer contrast but it will also make it easier to adopt the use of it in many systems.
We made a five blade single crystal interferometer that incorporates both the MZ and DF geometries in one single perfect silicon crystal. By removing or adding neutron absorbing cadmium beamblocks we can choose either the MZ or DF equivalent (see Figure 1). This allows us to compare the MZ and DF under the same conditions.
Calculations show that the DF configuration is much less sensitive to low frequency vibrations. For the DF configuration the contrast does eventually fall off at high frequencies, which can be easily damped with small, commercially available systems. The decrease in sensitivity to vibrations in the DF case is due to the fact that any change in momentum caused by vibrating blades in the first loop is compensated by the same change in the second loop. In the MZ case this is not true. Figure 2 shows interferograms for the two cases. For the MZ case the fringe visibility becomes zero at only 8Hz while at the same frequency the DF still has optimal visibility.
These results demonstrate a concrete example of how quantum information theory can control the effects of noise on useful macroscopic quantum devices. They validate our expectations that a quantum code can improve coherent control in neutron interferometry. The DF interferometer's insensitivity to vibration will enable it to be placed closer to the guide, thereby recovering neutron intensity by having a larger solid angle reach the detector. We anticipate relying on this and related quantum information theory approaches to construct a new series of compact neutron interferometer setups tailored to specific applications.
Figure 1: A schematic diagram of the 5-blade neutron interferometer. By changing the location of Cd beam blocks we can switch from a MZ and DF type interferometer without having to use completely different interferometer crystals.
Figure 2: The fringe visibility for the MZ (top) and DF (bottom) type geometries. The DF type is insensitive to vibrations while MZ is clearly not.