Controlling the multiport nature of Bragg diffraction in atom interferometry

Abstract

Bragg diffraction has been used in atom interferometers because it allows signal enhancement through multiphoton momentum transfer and suppression of systematics by not changing the internal state of atoms. Its multi-port nature, however, can lead to parasitic interferometers, allows for intensity-dependent phase shifts in the primary interferometers, and distorts the ellipses used for phase extraction. We study and suppress these unwanted effects. Specifically, phase extraction by ellipse fitting and the resulting systematic phase shifts are calculated by Monte Carlo simulations. Phase shifts arising from the thermal motion of the atoms are controlled by spatial selection of atoms and an appropriate choice of Bragg intensity. In these simulations, we found that Gaussian Bragg pulse shapes yield the smallest systematic shifts. Parasitic interferometers are suppressed by a "magic" Bragg pulse duration. The sensitivity of the apparatus was improved by the addition of AC Stark shift compensation, which permits direct experimental study of sub-part-per-billion (ppb) systematics. This upgrade allows for a 310 k momentum transfer, giving an unprecedented 6.6 Mrad measured in a Ramsey-Bordé interferometer.Atom interferometers have been used for tests of fundamental physics such as the isotropy of gravity [1], the equivalence principle [2][3][4][5], the search for dark-sector particles [6,7], and measurements of the fine structure constant α [8,9], which characterizes the strength of the electromagnetic interaction. This constant can be obtained from the electron's gyromagnetic anomaly g e − 2. At the current accuracy, this involves > 10,000 Feynman diagrams, as well as muonic and hadronic physics [10]. At increased accuracy, the tauon and the weak interaction will also be included. Since this path leads to 0.24 ppb accuracy [11], an independent measurement of α would create a unique test for the standard model. The best such measurements of α are currently based on the recoil energy 2 k 2 /2m At of an atom of mass m At that has scattered a photon of momentum k [12,13]. This measurement yields /m At , and yields α to 0.66 ppb [8] via the relationThe Rydberg constant R ∞ is known to 0.005 ppb accuracy, and the atom-to-electron mass ratio is known to better than 0.1 ppb for many species [14]. In this paper, we improve the accuracy of a measurement of the fine structure constant using Bragg diffraction, by both increasing the sensitivity of the experiment and a thorough theoretical analysis of important systematic effects. In Section I, we present an enhancement in the sensitivity of an atom interferometer (AI) by AC Stark compensation, which allows faster integration. In Section II, we investigate aberrations to the elliptical shape used for phase extraction which arise from the diffraction phase. Section III shows how this leads to phase shifts due to thermal motion, and Section IV describes how spatial filtering can be used to suppress those shifts. In Section V, we consider the influence of the Bragg pulse shape, and i...

Measurement of the fine-structure constant as a test of the Standard Model

“…Coriolis-force compensation suppresses the effect of Earth's rotation. In addition, we have applied ac-Stark shift compensation (16,17) and demonstrated a new spatial-filtering technique to reduce sources of decoherence, further enhance the sensitivity, and suppress systematic phase…”

“…In between the second and the third pulse, we accelerate the atom groups further from one another, using Bloch oscillations in accelerated optical lattices, to increases the sensitivity and suppress systematic effects. This transfers +2Nћk of momentum to the upper interferometer and -2Nћk to the lower (16).…”

Improving the accuracy of atom interferometers with ultracold sources

“…In the case of beamsplitters based on Bragg transitions, intensity inhomogeneities lead to even larger parasitic interferometer phase shifts. The impact of these diffraction phases and strategies for their mitigation have been studied in detail, for example in [13][14][15]. More, for noisy wavefronts with short scale phase fluctuations, such as due to the use of poor quality optics, local correlations building up in the laser beam during its propagation between intensity and phase fluctuations may lead to a bias in the phase of atom interferometers, as shown recently in [16].…”

Multiaxis atom interferometry with a single-diode laser and a pyramidal magneto-optical trap

“…Light-pulse atom interferometers (AIs) [1] use the recoil momentum from photon-atom interactions to coherently split and recombine matter waves. They have been used for measuring gravity [2][3][4], the gravity gradient [5][6][7], rotation [8][9][10], fundamental constants [11][12][13][14][15], and for testing fundamental laws of physics [16][17][18][19][20][21][22][23][24]. Since the laser wavelength defines the photon momentum with high precision, AIs are accurate.…”