Atom interferometer
Encyclopedia
An Atom interferometer is an interferometer based on exploiting the wave character of atoms. Interferometers are often used to make high-precision comparisons of distances. This can be used to constrain fundamental constants like the Gravitational Constant
or possibly to detect Gravitational Waves.
inherently depends on the wave
nature of the object. As pointed out by de Broglie
in his PhD-thesis, particles, including atom
s, can behave like waves (the so called Wave-particle duality, according to the general framework of quantum mechanics
). More and more high precision experiments now employ atom interferometers due to their short de Broglie wavelength. Some experiments are now even using molecule
s to obtain even shorter de Broglie wavelengths and to search for the limits of quantum mechanics. In many experiments with atoms, the roles of matter and light are reversed compared to the laser
based interferometers, i.e. the beam splitter and mirrors are lasers while the source instead emits matter waves (the atoms).
, atoms are affected much more strongly by gravity. In some apparatuses, the atoms are ejected upwards and the interferometry takes place while the atoms are in flight, or while falling in free flight. In other experiments gravitational effects by free acceleration are not negated; additional forces are used to compensate for gravity. While these guided systems in principle can provide arbitrary amounts of measurement time, their quantum coherence is still under discussion. Recent theoretical studies indicate that coherence is indeed preserved in the guided systems, but this has yet to be experimentally confirmed.
The early atom interferometers deployed slits or wires for the beam splitters and mirrors. Later systems, especially the guided ones, used light forces for splitting and reflecting of
the matter wave.
in Braunschweig, Germany. The largest physical separation between the partial wave packets of atoms was achieved using laser cooling techniques and stimulated Raman processes by S. Chu and coworkers in Stanford.
Gravitational constant
The gravitational constant, denoted G, is an empirical physical constant involved in the calculation of the gravitational attraction between objects with mass. It appears in Newton's law of universal gravitation and in Einstein's theory of general relativity. It is also known as the universal...
or possibly to detect Gravitational Waves.
Overview
InterferometryInterferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...
inherently depends on the wave
Wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
nature of the object. As pointed out by de Broglie
Louis, 7th duc de Broglie
Louis-Victor-Pierre-Raymond, 7th duc de Broglie, FRS was a French physicist and a Nobel laureate in the year 1929. He was the sixteenth member elected to occupy seat 1 of the Académie française in 1944, and served as Perpetual Secretary of the Académie des sciences, France.-Biography :Louis de...
in his PhD-thesis, particles, including atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s, can behave like waves (the so called Wave-particle duality, according to the general framework of quantum mechanics
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
). More and more high precision experiments now employ atom interferometers due to their short de Broglie wavelength. Some experiments are now even using molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
s to obtain even shorter de Broglie wavelengths and to search for the limits of quantum mechanics. In many experiments with atoms, the roles of matter and light are reversed compared to the laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
based interferometers, i.e. the beam splitter and mirrors are lasers while the source instead emits matter waves (the atoms).
Interferometer types
While the use of atoms offers easy access to high frequencies (and thus accuracies) than lightLight
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, atoms are affected much more strongly by gravity. In some apparatuses, the atoms are ejected upwards and the interferometry takes place while the atoms are in flight, or while falling in free flight. In other experiments gravitational effects by free acceleration are not negated; additional forces are used to compensate for gravity. While these guided systems in principle can provide arbitrary amounts of measurement time, their quantum coherence is still under discussion. Recent theoretical studies indicate that coherence is indeed preserved in the guided systems, but this has yet to be experimentally confirmed.
The early atom interferometers deployed slits or wires for the beam splitters and mirrors. Later systems, especially the guided ones, used light forces for splitting and reflecting of
the matter wave.
Examples
| Group | Year | Atomic Species | Method | Measured effect(s) |
|---|---|---|---|---|
| Pritchard | 1991 | Na Sodium Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride... , Na2 |
Nano-fabricated gratings Diffraction grating In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as... |
Polarizability, Index of Refraction |
| Zeilinger | Ar Argon Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide... |
Classical fringes behind three gratings | Gravity: Sagnac Sagnac effect The Sagnac effect , named after French physicist Georges Sagnac, is a phenomenon encountered in interferometry that is elicited by rotation. The Sagnac effect manifests itself in a setup called ring interferometry. A beam of light is split and the two beams are made to follow a trajectory in... :  |
|
| Sterr | Ramsey-Bordé | Polarizability, Aharanov-Effect: exp/theo  ,Sagnac  |
||
| Kasevich | Doppler Doppler effect The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from... on falling atoms |
Gravimeter Gravimeter A gravimeter or gravitometer is an instrument used in gravimetry for measuring the local gravitational field of the Earth. A gravimeter is a type of accelerometer, specialized for measuring the constant downward acceleration of gravity, which varies by about 0.5% over the surface of the Earth... :  Rotation:  ,fine structure constant:  |
||
| Berman | Talbot-Lau |
History
The separation of matter wave packets from complete atoms was first observed by Esterman and Stern in 1930, when a Na beam was diffracted of a surface on NaCl. The first modern atom interferometer reported was a Young double slit experiment with metastable helium atoms and a microfabricated double slit by Carnal and Mlynek in 1991, and an interferometer using three microfabricated diffraction gratings and Na atoms in the group around Pritchard at MIT. Shortly afterwards, an optical version of Ramsey spectrometer typically used in atomic clocks was recognized also as an atom interferometer at the PTBPhysikalisch-Technische Bundesanstalt
The Physikalisch-Technische Bundesanstalt is based in Braunschweig and Berlin. It is the national institute for natural and engineering sciences and the highest technical authority for metrology and physical safety engineering in Germany....
in Braunschweig, Germany. The largest physical separation between the partial wave packets of atoms was achieved using laser cooling techniques and stimulated Raman processes by S. Chu and coworkers in Stanford.
See also
- Electron interferometerElectron interferometerAn Electron interferometer is an interferometer based on exploiting the wave character of electrons.-Overview:Interferometry inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD-thesis, particles, including electrons can behavelike waves...
- C. S. Adams, M. Sigel & J. Mlynek, "Atom Optics", Phys. Rep. 240, 143 (1994). Overview of the atom-light interaction
- P. R. Berman [Editor], Atom Interferometry. Academic Press (1997). Detailed overview of atom interferometers at that time (good introductions and theory).
- Stedman Review of the Sagnac Effect