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Physics Today

Atom Interferometers Prove Their Worth in Atomic Measurements

Barbara Goss Levi

Published Jul 1, 1995• 6 citations
Publisher

Abstract

Thanks to the wave nature of matter, it's possible to build the atomic analog of an optical interferometer, although it's extremely difficult, because the de Broglie wavelengths of atoms are typically 10 000 times shorter than those of light. The feat was accomplished four years ago by a number of groups, each with a different scheme for splitting and recombining the matter waves. (See PHYSICS TODAY, July 1991, page 17.) We are now starting to see the fulfillment of the hopes raised by those first atom interferometers as researchers hone their interferometers to yield ever more precise values of fundamental constants or explore fundamental aspects of quantum mechanics such as Berry's phase. For example, Steven Chu and his colleagues at Stanford University have measured the ratio h/m of Planck's constant to the mass of a cesium atom with a precision of one part in 107, although the systematic errors are at the level of 1 part in 106. An experiment to improve the absolute accuracy of the h/m measurement to a few parts in 109 is underway. This ratio is one factor in the determination of the finestructure constant.

DOI
10.1063/1.2808088

Related papers

Atoms are the New Wave in Interferometers

Barbara Goss Levi

Interferometers based on matter waves are just the kind of precision tools needed to hone the cutting edge of physics. The de Broglie wavelengths of atoms, for example, are about 10 000 times shorter than those of light, and they offer correspondingly greater sensitivity. Electron and neutron interferometers have been around for some time, but atom interferometers have remained just out of grasp.

Physics Today•Jul 1, 1991•8 citations

Opportunity knocks for atomic interferometers

H. Fearn, Marian O. Scully

Optical interference is proof of the wave nature of light and matter–wave interferometers have also been shown to work for electrons and neutrons (by exploiting the de Broglie wavelength of the particles). Now a working interferometer for atoms has been demonstrated at the Massachusetts Institute of Technology(MIT) for the first time, in the sense that it uses “atomic beam splitters” to separate and recombine atomic beams (David W Keith et al. Phys. Rev. Lett. (1991) 66 2693). A simpler experiment at Konstanz University, Germany (O Carnal and J Mlynek Phys. Rev. Lett. (1991) 66 2689) has also demonstrated interference phenomena in atomic beams but a detailed description of the apparatus is not yet published. Atom interferometers will some day be useful in precision metrology, mass tomography, precision gyroscopes, general relativity, fundamental quantum mechanics and atomic physics.

Physics World•Aug 1, 1991•0 citations

Precision atom interferometry

Achim Peters, Keng Yeow Chung, Brent C. Young +2 more

The basic physical principles behind atom interferometers based on optical pulses of light are summarized. This method of atom interferometry is based on measurements in the time and frequency domain and is an inherently precise measurement technique. After a brief discussion of some of the important technical requirements for good fringe accuracy and visibility, we describe an interferometer that has measured the acceleration of an atom due to gravity with a resolution better than one part in 1010. We project that the absolute accuracy of our measurement will be of the order of a few parts in 109. We also describe an interferometer experiment that measures the recoil energy shift of an atom when it absorbs a photon. When combined with the value of the Rydberg constant and the mass ratios MCs/mp and mp/me, one can obtain a value for α, the fine structure constant. Currently, we have an experimental resolution Δα/α ∼ 10-8 after two hours of integration time and are studying the systematic effects that affect the measurement.

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences•Dec 15, 1997•81 citations

Atom Interferometry

Peter Hannaford

Matter - wave interferometry began with the development of electron interferometers and neutron interferometers in the 1950s and 1960s, but it wasn't until 1991 that the first atom matter - wave interferometer was realized. This was followed by a surge of activity sparked by the advent of sources of ultracold laser-cooled atoms. Some of the potential advantages of atom interferometry over neutron interferometry include: much higher particle fluxes, lower particle velocities, larger particle masses, particles with internal states, and laboratory-based sources. This volume is the first text on atom interferometry. It consists of ten comprehensive review articles by leading researchers in the field, many of whom pioneered the first atom interferometers in 1991. The articles describe the different types of atom interferometers developed to date, ranging from the three-grating Mach - Zehnder interferometer based on nanofabricated grating structures (MIT) or standing-wave light-field gratings (Innsbruck), to the Talbot - Lau atom interferometer (Berkeley and Michigan), to atom interferometers based on internal-state labelling such as separated light-field interferometers (PTB, Hannover and Paris-Nord) and light-pulse interferometers (Stanford). Some of the recent applications of atom interferometry described in the articles include high precision measurements of rotations, the gravitational acceleration, and the fine structure constant (Stanford); measurements of topological phases (PTB and Hannover); correlation experiments with atoms and photons (Konstanz) and with pairs of atoms (Tokyo); holographic manipulation of atoms (Tokyo); and experiments on the quantum theory of measurement (Garching, Harvard and Texas A&M). In summary, this volume provides an excellent up-to-date account of atom interferometry and is recommended as essential reading for all researchers and would-be researchers in the field. At the same time it contains sufficient background material and theory to serve as an excellent introduction for the non-specialist. The field is presently moving at such a rapid pace, however, that many of the latest results reported in this volume will already have been superseded by the time it reaches the library shelves.

Measurement Science and Technology•Sep 1, 1997•1 citation

Atom Interferometer Measures G with Same Accuracy as Optical Devices

Barbara Goss Levi

The acceleration due to gravity, g, can be measured simply by timing how long it takes an object to fall. One can accomplish this with great precision by orienting an optical interferometer so that one of its arms is vertical. If the mirror in that arm is then allowed to fall pan way, a Doppler shift in the reflected light signals its rate of fall. A similar measurement can now be done just as accurately with falling atoms (whose atomic frequencies are Doppler shifted), thanks to a long-term effort by a group at Stanford University. Achim Peters, Keng Yeow Chung, and Steven Chu recently reported that their atom interferometer has determined g to within three parts per billion.

Physics Today•Nov 1, 1999•6 citations

Measurements of Atomic Beam Velocities with Phase Choppers and Precision Measurements of Alkali Atomic Polarizabilities

Ivan Hromada

Atom interferometers, in which de Broglie waves are coherently split and recombined to make interference fringes, now serve as precision measurement tools for several quantities in physics. Examples include measurements of Newton's constant, the fine structure constant, van der Waals potentials, and atomic polarizabilities. To make next-generation measurements of static electric dipole atomic polarizabilities with an atom beam interferometer, I worked on new methods to precisely measure the velocity distribution for atom beams. I will explain how I developed and used phase choppers to measure lithium, sodium, potassium, and cesium atomic beam velocities with 0.07% accuracy. I also present new measurements of polarizability for these atoms. I classify systematic errors into two broad categories: (1) fractional errors that are similar for all different types of atoms in our experiments, and (2), errors that scale with de Broglie wavelength or inverse atomic momentum in our experiments. This distinction is important for estimating the uncertainty in our measurements of ratios of atomic polarizabilities, e.g., αCs / αNₐ = 2.488(12).

•Jan 1, 2014•0 citations
Thanks to the wave nature of matter, it's possible to build the atomic analog of an optical interferometer, although it's extremely difficult, because the de Broglie wavelengths of atoms are typically 10 000 times shorter than those of light. The feat was accomplished four years ago by a number of groups, each with a different scheme for splitting and recombining the matter waves. (See PHYSICS TODAY, July 1991, page 17.) We are now starting to see the fulfillment of the hopes raised by those first atom interferometers as researchers hone their interferometers to yield ever more precise values of fundamental constants or explore fundamental aspects of quantum mechanics such as Berry's phase. For example, Steven Chu and his colleagues at Stanford University have measured the ratio h/m of Planck's constant to the mass of a cesium atom with a precision of one part in 107, although the systematic errors are at the level of 1 part in 106. An experiment to improve the absolute accuracy of the h/m measurement to a few parts in 109 is underway. This ratio is one factor in the determination of the finestructure constant.
Optical interference is proof of the wave nature of light and matter–wave interferometers have also been shown to work for electrons and neutrons (by exploiting the de Broglie wavelength of the particles). Now a working interferometer for atoms has been demonstrated at the Massachusetts Institute of Technology(MIT) for the first time, in the sense that it uses “atomic beam splitters” to separate and recombine atomic beams (David W Keith et al. Phys. Rev. Lett. (1991) 66 2693). A simpler experiment at Konstanz University, Germany (O Carnal and J Mlynek Phys. Rev. Lett. (1991) 66 2689) has also demonstrated interference phenomena in atomic beams but a detailed description of the apparatus is not yet published. Atom interferometers will some day be useful in precision metrology, mass tomography, precision gyroscopes, general relativity, fundamental quantum mechanics and atomic physics.
The basic physical principles behind atom interferometers based on optical pulses of light are summarized. This method of atom interferometry is based on measurements in the time and frequency domain and is an inherently precise measurement technique. After a brief discussion of some of the important technical requirements for good fringe accuracy and visibility, we describe an interferometer that has measured the acceleration of an atom due to gravity with a resolution better than one part in 1010. We project that the absolute accuracy of our measurement will be of the order of a few parts in 109. We also describe an interferometer experiment that measures the recoil energy shift of an atom when it absorbs a photon. When combined with the value of the Rydberg constant and the mass ratios MCs/mp and mp/me, one can obtain a value for α, the fine structure constant. Currently, we have an experimental resolution Δα/α ∼ 10-8 after two hours of integration time and are studying the systematic effects that affect the measurement.
Matter - wave interferometry began with the development of electron interferometers and neutron interferometers in the 1950s and 1960s, but it wasn't until 1991 that the first atom matter - wave interferometer was realized. This was followed by a surge of activity sparked by the advent of sources of ultracold laser-cooled atoms. Some of the potential advantages of atom interferometry over neutron interferometry include: much higher particle fluxes, lower particle velocities, larger particle masses, particles with internal states, and laboratory-based sources. This volume is the first text on atom interferometry. It consists of ten comprehensive review articles by leading researchers in the field, many of whom pioneered the first atom interferometers in 1991. The articles describe the different types of atom interferometers developed to date, ranging from the three-grating Mach - Zehnder interferometer based on nanofabricated grating structures (MIT) or standing-wave light-field gratings (Innsbruck), to the Talbot - Lau atom interferometer (Berkeley and Michigan), to atom interferometers based on internal-state labelling such as separated light-field interferometers (PTB, Hannover and Paris-Nord) and light-pulse interferometers (Stanford). Some of the recent applications of atom interferometry described in the articles include high precision measurements of rotations, the gravitational acceleration, and the fine structure constant (Stanford); measurements of topological phases (PTB and Hannover); correlation experiments with atoms and photons (Konstanz) and with pairs of atoms (Tokyo); holographic manipulation of atoms (Tokyo); and experiments on the quantum theory of measurement (Garching, Harvard and Texas A&M). In summary, this volume provides an excellent up-to-date account of atom interferometry and is recommended as essential reading for all researchers and would-be researchers in the field. At the same time it contains sufficient background material and theory to serve as an excellent introduction for the non-specialist. The field is presently moving at such a rapid pace, however, that many of the latest results reported in this volume will already have been superseded by the time it reaches the library shelves.
The acceleration due to gravity, g, can be measured simply by timing how long it takes an object to fall. One can accomplish this with great precision by orienting an optical interferometer so that one of its arms is vertical. If the mirror in that arm is then allowed to fall pan way, a Doppler shift in the reflected light signals its rate of fall. A similar measurement can now be done just as accurately with falling atoms (whose atomic frequencies are Doppler shifted), thanks to a long-term effort by a group at Stanford University. Achim Peters, Keng Yeow Chung, and Steven Chu recently reported that their atom interferometer has determined g to within three parts per billion.
Atom interferometers, in which de Broglie waves are coherently split and recombined to make interference fringes, now serve as precision measurement tools for several quantities in physics. Examples include measurements of Newton's constant, the fine structure constant, van der Waals potentials, and atomic polarizabilities. To make next-generation measurements of static electric dipole atomic polarizabilities with an atom beam interferometer, I worked on new methods to precisely measure the velocity distribution for atom beams. I will explain how I developed and used phase choppers to measure lithium, sodium, potassium, and cesium atomic beam velocities with 0.07% accuracy. I also present new measurements of polarizability for these atoms. I classify systematic errors into two broad categories: (1) fractional errors that are similar for all different types of atoms in our experiments, and (2), errors that scale with de Broglie wavelength or inverse atomic momentum in our experiments. This distinction is important for estimating the uncertainty in our measurements of ratios of atomic polarizabilities, e.g., αCs / αNₐ = 2.488(12).