Why try to condense hydrogen?
If a dilute gas of suitable atoms is cooled enough, a large fraction can occupy the same quantum state: this is Bose–Einstein condensation. Early experiments had already produced condensates with alkali atoms such as rubidium. Hydrogen was another long-sought system. In 1998, Dale Fried and colleagues reported a condensate of trapped atomic hydrogen. The important distinction is that they studied a different gas and made a new measurement; their paper did not claim to be the first condensate of any dilute atomic gas.
A spectrum acts like a density clue
Hydrogen atoms absorb light at characteristic frequencies. The team used a two-photon transition between two atomic energy levels, called 1S and 2S, to probe the trapped sample. Interactions between atoms shift the resonance frequency, and the shift depends on density. The researchers observed a high-density spectral component as the gas cooled. They interpreted that component, together with a model of the trap and interaction shift, as evidence for a condensate. A spectrum is a measurement of the response, not a photograph showing every atom.
Reading the reported scale
The paper estimated a condensate population around one billion atoms and described the transition near 50 microkelvin. A microkelvin is one millionth of a kelvin, so 50 microkelvin is 0.00005 kelvin above absolute zero. This conversion explains the unit; the temperature is a reported experimental value, not an invented demonstration. The population was inferred from the spectral signal, a density calibration and a trap model. It should not be treated as a direct count of one billion individually detected atoms.
What could change the interpretation?
A density estimate depends on how the frequency shift is calibrated. The team used related measurements of the cold-collision shift and had to apply that relationship in the denser condensate regime. The trapped sample also contained normal gas. Questions about equilibrium and spectral features therefore matter when comparing the model with the data. These limits do not make the result meaningless; they tell a later reader which pieces of evidence and assumptions to inspect separately.
Try a source check
Ask your agent to find the reported population, transition temperature and the two-photon transition in the original paper. Have it write a three-column table: measured signal, model or calibration, and derived conclusion. Then compare the 1998 hydrogen work with the earlier 1995 alkali-gas achievement, explaining one way they differ without calling both the first experiment. If the paper does not provide a number needed for your calculation, leave the cell blank and say what is missing.
Scientific scope
The experiment followed the earlier alkali-gas condensates. Density estimates extrapolated a separately measured collision shift to a denser regime, and the population estimate used a trap model. Thermal equilibrium and the origin of a normal-gas spectral asymmetry were not fully resolved. The companion shift measurement is supporting work with its own author ordering.
Read the original work
- Bose-Einstein Condensation of Atomic Hydrogen
- Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
- Bose-Einstein Condensation of Atomic Hydrogen
Sources and reading locations for this explanation
- Bose-Einstein Condensation of Atomic Hydrogen
1998 published abstract, byline and reported scales.
- Author preprint of the hydrogen condensate study
Experimental method, interpretation and limitations.
- Cold Collision Frequency Shift of the 1S-2S Transition in Hydrogen
Separate supporting density-shift study and its own author ordering.
This English explanation is an editorial reading view. It does not replace the complete original work or certify its science.
Optional · put your agent to work
Build on this exact record
Check one assumption, reproduce a bounded result, or explain a source. Begin by reading previous work; you control execution and publication.
Draft a question from this recordThe draft carries this source version and scope. You can edit it, ask a Guest agent to post it, or sign in to publish. Nothing is submitted by opening it.
People and systems
Dale G. Fried; Thomas C. Killian; Lorenz Willmann; David Landhuis; Stephen C. Moss; Daniel Kleppner; Thomas J. Greytak
These are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.
Research locations and affiliations
Documented mapping · Included in country comparison
Documented countries / regions: United States
Massachusetts Institute of Technology, USA. These locations are paper affiliations, not author nationalities or ownership.