Matt Jaffe

Atom-interferometry constraints on dark energy

Limiting unknows in the dark side Our knowledge of the inventory of stuff that makes up our universe amounts to a humbling 5%. The rest consists of either dark energy (~70%) or dark matter (~25%). Using atom interferometry, Hamilton et al. describe the results of experiments that controlled for dark energy screening mechanisms in individual atoms, not bulk matter. Aprile et al. report on an analysis of data taken with the XENON100 detectors aiming to identify dark matter particles directly by monitoring their rare interaction with ordinary matter. In this setup, a large underground tank of liquid xenon forms a target for weakly interacting m assive particles. These combined results set limits on several types of proposed dark matter and dark energy candidates (see the Perspective by Schmiedmayer and Abele). Science, this issue p. 849, p. 851; see also p. 786 Cold atom experiments can constrain proposed theories of dark energy. [Also see Perspective by Schmiedmayer and Abele] If dark energy, which drives the accelerated expansion of the universe, consists of a light scalar field, it might be detectable as a “fifth force” between normal-matter objects, in potential conflict with precision tests of gravity. Chameleon fields and other theories with screening mechanisms, however, can evade these tests by suppressing the forces in regions of high density, such as the laboratory. Using a cesium matter-wave interferometer near a spherical mass in an ultrahigh-vacuum chamber, we reduced the screening mechanism by probing the field with individual atoms rather than with bulk matter. We thereby constrained a wide class of dark energy theories, including a range of chameleon and other theories that reproduce the observed cosmic acceleration.

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.

Testing sub-gravitational forces on atoms from a miniature in-vacuum source mass

Atomic interferometry measurements of the gravitational force on free-falling atoms provide improved constraints on certain scalar field theories trying to explain dark energy.

Chameleon dark energy and atom interferometry

Atom interferometry experiments are searching for evidence of chameleon scalar fields with ever-increasing precision. As experiments become more precise, so too must theoretical predictions. Previous work has made numerous approximations to simplify the calculation, which in general requires solving a three-dimensional nonlinear partial differential equation. This paper calculates the chameleonic force using a numerical relaxation scheme on a uniform grid. This technique is more general than previous work, which assumed spherical symmetry to reduce the partial differential equation to a one-dimensional ordinary differential equation. We examine the effects of approximations made in previous efforts on this subject and calculate the chameleonic force in a setup that closely mimics the recent experiment of Hamilton et al. Specifically, we simulate the vacuum chamber as a cylinder with dimensions matching those of the experiment, taking into account the backreaction of the source mass, its offset from the center, and the effects of the chamber walls. Remarkably, the acceleration on a test atomic particle is found to differ by only 20% from the approximate analytical treatment. These results allow us to place rigorous constraints on the parameter space of chameleon field theories, although ultimately the constraint we find is the same as the one we reported in Hamilton et al. because we had slightly underestimated the size of the vacuum chamber. This computational technique will continue to be useful as experiments become even more precise and will also be a valuable tool in optimizing future searches for chameleon fields and related theories.

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.

Attractive force on atoms due to blackbody radiation

Objects at finite temperature emit thermal radiation with an outward energy–momentum flow, which exerts an outward radiation pressure. At room temperature, a caesium atom scatters on average less than one of these blackbody radiation photons every 108 years. Thus, it is generally assumed that any scattering force exerted on atoms by such radiation is negligible. However, atoms also interact coherently with the thermal electromagnetic field. In this work, we measure an attractive force induced by blackbody radiation between a caesium atom and a heated, centimetre-sized cylinder, which is orders of magnitude stronger than the outward-directed radiation pressure. Using atom interferometry, we find that this force scales with the fourth power of the cylinder’s temperature. The force is in good agreement with that predicted from an a.c. Stark shift gradient of the atomic ground state in the thermal radiation field1. This observed force dominates over both gravity and radiation pressure, and does so for a large temperature range.The effect of blackbody radiation is expected to be very weak. The acceleration due to the attractive optical forces from blackbody radiation is measured in an atom interferometer and, surprisingly, it dominates gravity and radiation pressure