Bose–Einstein condensate
In 1924, Satyendra Nath Bose sent a paper to Albert Einstein regarding the quantum statistics of light quanta. Bose derived Planck's quantum radiation law without any reference to classical physics. Einstein was impressed by this work and translated the paper himself from English to German. He submitted it for Bose to the Zeitschrift für Physik, which published it in 1924. Einstein then extended Bose's ideas to matter in two other papers. The result of their efforts is the concept of a Bose gas. This gas is governed by Bose, Einstein statistics. These statistics describe the statistical distribution of identical particles with integer spin. Now called bosons, these particles are allowed to share a quantum state. Einstein proposed that cooling bosonic atoms to a very low temperature would cause them to fall into the lowest accessible quantum state. This process results in a new form of matter known as condensation.
On the 5th of June 1995, Eric Cornell and Carl Wieman produced the first gaseous condensate at the University of Colorado Boulder NIST, JILA lab. They used rubidium atoms cooled to 170 nanokelvins. Shortly thereafter, Wolfgang Ketterle at MIT produced a Bose, Einstein Condensate in a gas of sodium atoms. For their achievements, Cornell, Wieman, and Ketterle received the 2001 Nobel Prize in Physics. Bose-Einstein condensation of alkali gases is easier because they can be pre-cooled with laser cooling techniques. Unlike atomic hydrogen at the time, which gave a significant head start when performing the final forced evaporative cooling to cross the condensation threshold. These early studies founded the field of ultracold atoms. Hundreds of research groups around the world now routinely produce BECs of dilute atomic vapors in their labs.
The transition to BEC occurs below a critical temperature for a uniform three-dimensional gas consisting of non-interacting particles. The formula for this temperature depends on particle density and mass per boson. It also involves the reduced Planck constant and the Boltzmann constant. Interactions shift the value, and corrections can be calculated by mean-field theory. This formula is derived from finding the gas degeneracy in the Bose gas using Bose, Einstein statistics. A more concise condition involves phase-space density. Phase-space density is a dimensionless quantity involving the thermal de Broglie wavelength. The transition to BEC occurs when the phase-space density exceeds a critical value. In 3D uniform space, this critical value relates directly to the peak density. In a 3D harmonic potential, the critical value changes based on the specific geometry of the trap.
In 1938, Pyotr Kapitsa, John Allen, and Don Misener discovered that helium-4 became a new kind of fluid at temperatures less than 2.17 K. Superfluid helium has many unusual properties including zero viscosity. It also exhibits quantized vortices. It was quickly believed that superfluidity was due to partial Bose, Einstein condensation of the liquid. Many properties of superfluid helium appear in gaseous condensates created by Cornell, Wieman, and Ketterle. Superfluid helium-4 is a liquid rather than a gas. This means interactions between atoms are relatively strong. The original theory of Bose, Einstein condensation must be heavily modified to describe it. Yet Bose, Einstein condensation remains fundamental to the superfluid properties of helium-4. Note that helium-3 enters a superfluid phase which can be explained by formation of bosonic Cooper pairs.
Bose, Einstein condensation applies to quasiparticles in solids such as magnons, excitons, and polaritons. These particles have integer spin so they form condensates. Magnons are electron spin waves that can be controlled by a magnetic field. In 1999, condensation was demonstrated in antiferromagnetic materials at temperatures as great as 14 K. In 2006, condensation in a ferromagnetic yttrium-iron-garnet thin film was seen even at room temperature. Excitons were predicted to condense at low temperature and high density by Boer et al. in 1961. Bilayer system experiments first demonstrated condensation in 2003. Fast optical exciton creation formed condensates in sub-kelvin conditions in 2005. Polariton condensation was first detected for exciton-polaritons in a quantum well microcavity kept at 5 K. Quasiparticle BECs have been achieved at room-temperature in microcavity-coupled organic semiconductors.
In June 2020, the Cold Atom Laboratory experiment on board the International Space Station successfully created a BEC of rubidium atoms. They observed them for over a second in free-fall. Although initially just a proof of function, early results showed interesting phenomena. In the microgravity environment of the ISS, about half of the atoms formed into a magnetically insensitive halo-like cloud around the main body of the BEC. The first demonstration of a BEC in weightlessness was achieved in 2008 at a drop tower in Bremen, Germany. A consortium of researchers led by Ernst M. Rasel from Leibniz University Hannover conducted this work. The same team demonstrated in 2017 the first creation of a Bose, Einstein Condensate in space. It is also the subject of two upcoming experiments on the International Space Station.
In 1999, Danish physicist Lene Hau led a team from Harvard University which slowed a beam of light to about 17 meters per second using a superfluid. Hau and her associates recorded the light's phase and amplitude recovered by a second nearby condensate. Another current research interest is creating Bose, Einstein condensates in microgravity for high precision atom interferometry. Researchers in the new field of atomtronics use properties of Bose, Einstein condensates in matter-wave circuits. In 1970, BECs were proposed by Emmanuel David Tannenbaum for anti-stealth technology. Continuous BEC was achieved for the first time in 2022 with specific isotopes. Limitations of evaporative cooling have restricted atomic BECs to pulsed operation involving highly inefficient duty cycles. Achieving continuous BEC enables new sensing applications through high flux and coherence matter waves produced continuously.
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Common questions
Who invented Bose-Einstein condensate and when was it first created?
Satyendra Nath Bose and Albert Einstein developed the theoretical concept of Bose-Einstein condensate in 1924. Eric Cornell and Carl Wieman produced the first gaseous condensate on the 5th of June 1995 at the University of Colorado Boulder NIST, JILA lab.
What temperature is required to create a Bose-Einstein condensate from rubidium atoms?
Rubidium atoms must be cooled to 170 nanokelvins to form a Bose-Einstein condensate. This process occurs below a critical temperature that depends on particle density and mass per boson.
How does superfluid helium-4 relate to Bose-Einstein condensation theory?
Superfluid helium-4 exhibits properties due to partial Bose-Einstein condensation of the liquid. The original theory requires heavy modification because interactions between atoms are relatively strong compared to gases.
Where can Bose-Einstein condensates be found in solid materials today?
Bose-Einstein condensates exist as quasiparticles such as magnons, excitons, and polaritons in solids. Condensation has been demonstrated in antiferromagnetic materials up to 14 K and even at room temperature in ferromagnetic yttrium-iron-garnet thin films.
When was the first Bose-Einstein condensate created in space?
The Cold Atom Laboratory experiment on board the International Space Station successfully created a Bose-Einstein condensate of rubidium atoms in June 2020. A consortium led by Ernst M. Rasel achieved the first creation of a Bose-Einstein condensate in space in 2017.