Brian Estey

Influence of the Coriolis force in atom interferometry.

In a light-pulse atom interferometer, we use a tip-tilt mirror to remove the influence of the Coriolis force from Earths rotation and to characterize configuration space wave packets. For interferometers with a large momentum transfer and large pulse separation time, we improve the contrast by up to 350% and suppress systematic effects. We also reach what is to our knowledge the largest space-time area enclosed in any atom interferometer to date. We discuss implications for future high-performance instruments.

A Clock Directly Linking Time to a Particle's Mass

Linking Mass and Time The precision of atomic clocks is based on the transitions between two well-defined energy levels—the frequency of oscillation. We know from relativity that mass and energy are equivalent and from quantum mechanics that energy relates to frequency. Therefore, the ticking of a clock can be related, in principle, to the mass of a particle. The oscillation frequency of a particle is known as its Compton frequency and, because of the high frequency involved and stability of atoms, it has been argued that a clock linking mass and time would offer very high precision. Ordinarily, the Compton frequency is extremely high and not accessible to direct excitation. Lan et al. (p. 554, published online 10 January; see the Perspective by Debs et al.) demonstrate the operation of a Compton clock exploiting a related parameter, the phase accumulation rate of cold cesium atoms. Using an atom interferometer and an optical frequency comb to bring the Compton frequency into an experimentally accessible regime, mass and time could be directly linked. A clock is demonstrated wherein the ticks are related to the mass of a cesium atom. [Also see Perspective by Debs et al.] Historically, time measurements have been based on oscillation frequencies in systems of particles, from the motion of celestial bodies to atomic transitions. Relativity and quantum mechanics show that even a single particle of mass m determines a Compton frequency ω0 = mc2/ℏ, where c is the speed of light and ℏ is Plancks constant h divided by 2π. A clock referenced to ω0 would enable high-precision mass measurements and a fundamental definition of the second. We demonstrate such a clock using an optical frequency comb to self-reference a Ramsey-Bordé atom interferometer and synchronize an oscillator at a subharmonic of ω0. This directly demonstrates the connection between time and mass. It allows measurement of microscopic masses with 4 × 10−9 accuracy in the proposed revision to SI units. Together with the Avogadro project, it yields calibrated kilograms.

Force-Free Gravitational Redshift: Proposed Gravitational Aharonov-Bohm experiment

We propose a feasible laboratory interferometry experiment with matter waves in a gravitational potential caused by a pair of artificial field-generating masses. It will demonstrate that the presence of these masses (and, for moving atoms, time dilation) induces a phase shift, even if it does not cause any classical force. The phase shift is identical to that produced by the gravitational redshift (or time dilation) of clocks ticking at the atoms Compton frequency. In analogy to the Aharonov-Bohm effect in electromagnetism, the quantum mechanical phase is a function of the gravitational potential and not the classical forces.

Atom interferometry in an optical cavity.

We demonstrate interference fringes using the first atom interferometer in an optical cavity. We discuss the advantages of using an optical cavity and applications ranging from inertial sensors to tests of gravity in quantum mechanics.

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

Refining the fine-structure constant The fine-structure constant, α, is a dimensionless constant that characterizes the strength of the electromagnetic interaction between charged elementary particles. Related by four fundamental constants, a precise determination of α allows for a test of the Standard Model of particle physics. Parker et al. used matter-wave interferometry with a cloud of cesium atoms to make the most accurate measurement of α to date. Determining the value of α to an accuracy of better than 1 part per billion provides an independent method for testing the accuracy of quantum electrodynamics and the Standard Model. It may also enable searches of the so-called “dark sector” for explanations of dark matter. Science, this issue p. 191 Atom interferometry provides a precise measurement of the fine-structure constant. Measurements of the fine-structure constant α require methods from across subfields and are thus powerful tests of the consistency of theory and experiment in physics. Using the recoil frequency of cesium-133 atoms in a matter-wave interferometer, we recorded the most accurate measurement of the fine-structure constant to date: α = 1/137.035999046(27) at 2.0 × 10−10 accuracy. Using multiphoton interactions (Bragg diffraction and Bloch oscillations), we demonstrate the largest phase (12 million radians) of any Ramsey-Bordé interferometer and control systematic effects at a level of 0.12 part per billion. Comparison with Penning trap measurements of the electron gyromagnetic anomaly ge − 2 via the Standard Model of particle physics is now limited by the uncertainty in ge − 2; a 2.5σ tension rejects dark photons as the reason for the unexplained part of the muon’s magnetic moment at a 99% confidence level. Implications for dark-sector candidates and electron substructure may be a sign of physics beyond the Standard Model that warrants further investigation.

High-Resolution Atom Interferometers with Suppressed Diffraction Phases.

We experimentally and theoretically study the diffraction phase of large-momentum transfer beam splitters in atom interferometers based on Bragg diffraction. We null the diffraction phase and increase the sensitivity of the interferometer by combining Bragg diffraction with Bloch oscillations. We demonstrate agreement between experiment and theory, and a 1500-fold reduction of the diffraction phase, limited by measurement noise. In addition to reduced systematic effects, our interferometer has high contrast with up to 4.4×10(6) radians of phase difference, and a resolution in the fine structure constant of δα/α=0.25  ppb in 25 h of integration time.

Concept of a miniature atomic sensor

We present preliminary results of our research program towards multi-axis quantum acceleration sensors in a compact package, using Bloch oscillations of matter waves to provide large momentum transfer. The projected performance is discussed. We demonstrate the first Mach-Zehnder atom interferometer in which a cavity mode is used for addressing the atoms.

Improved Accuracy of Atom Interferometry Using Bragg Diffraction

We study sub-part per billion systematic effects in a Bragg-diffraction atom interferometer relevant to a precision-measurement of the fine-structure constant. The multi-port nature of Bragg diffraction gives rise to parasitic interferometers, which we suppress using a “magic” Bragg pulse duration. The sensitivity of the apparatus is improved by the addition of AC Stark shift compensation, which permits direct experimental study of sub-ppb systematics. This upgrade allows for a 310~k momentum transfer, giving an unprecedented 6.6Mrad measured in a Ramsey-Bordé interferometer.