Abstract
Atom matterwave interferometry requires mirror and beamsplitter pulses that are robust to inhomogeneities in field intensity, magnetic environment, atom velocity and Zeeman sub-state. Pulse shapes determined using quantum control methods offer significantly improved interferometer performance by allowing broader atom distributions, larger interferometer areas and higher contrast. We have applied gradient ascent pulse engineering (GRAPE) to optimise the design of phase-modulated mirror pulses for a Mach-Zehnder light-pulse atom interferometer, with the aim of increasing fringe contrast when averaged over atoms with an experimentally relevant range of velocities, beam intensities, and Zeeman states. Pulses were found to be highly robust to variations in detuning and coupling strength, and offer a clear improvement in robustness over the best established composite pulses. The peak mirror fidelity in a cloud of $\sim 80\ \mu$K ${}^{85}$Rb atoms is predicted to be improved by a factor of 2 compared with standard rectangular $\pi$ pulses.
Highlights
Emerging quantum technologies require the coherent manipulation of quantum states
Various techniques have been developed in the field of nuclear magnetic resonance (NMR) spectroscopy to produce control pulses that are robust to variations in the interaction strength and detuning, and such techniques should be applicable to other systems, including the effective two-level schemes of atom interferometry
All pulse optimizations were carried out using gradient ascent pulse engineering (GRAPE) and Spinach, constraining the effective Rabi frequency to correspond to a limited laser power and fixed single-photon detuning, and with a discretization time step of 100 ns
Summary
Emerging quantum technologies require the coherent manipulation of quantum states. For example, ultraprecise coldatom-based sensors such as gravimeters, accelerometers, magnetometers, and gyroscopes [1,2,3,4] use interactions with laser pulses to form the beam splitters and mirrors of matterwave interferometers [5], and these “π/2” and “π ” pulses must operate with high fidelity if the best sensitivity is to be achieved by using pulse sequences to increase the interferometer area [6] or maximize the entanglement [7]. The fidelity of quantum state manipulation deteriorates when there are inhomogeneities in the interaction field, magnetic environment, atomic velocities, and quantum state distributions [8] This limits the number of control operations that can be performed before coherence is lost, so it is common to filter the atomic sample to restrict the variations experienced [6,9,10] by fewer atoms. In a feasibility study of the applicability of composite pulses to cold-atom interferometers, Dunning et al [8] analyzed the performance of various established NMR pulse sequences for inversion or “mirror” operations in a thermal cloud of 85Rb in a velocity-sensitive Raman arrangement subject to intensity variations and a distribution over Zeeman sublevels. It is expected that such optimal pulses should allow for greater interferometric areas, higher contrast, warmer samples, and increased interferometric sensitivities
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