Cold atoms and matter waves

Cold-atom experiments use laser cooling and related techniques to bring atoms near absolute zero, where their wave nature becomes prominent. They probe matter-wave interference, quantum coherence, and collective states of matter.

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Laser cooling: A family of methods that uses light to reduce the motion and temperature of atoms. Repeated photon absorption and emission slow atoms before matter-wave experiments.
De Broglie wavelength: The wavelength associated with a particle’s momentum, given by Planck’s constant divided by momentum. Cooling reduces atomic momentum and increases the wavelength until neighboring waves can overlap.
Precision measurement: Measurement designed to estimate physical quantities with carefully quantified uncertainty. Atomic wave phases enable sensitive measurements of acceleration, rotation, and gravity.
Bose–Einstein condensate: A state of bosonic matter in which a macroscopic number of particles occupy one quantum state. Its shared phase makes a cold gas behave as a coherent matter wave.
Thermal de Broglie wavelength: A characteristic wavelength set by a particle’s mass and the temperature of a thermal gas. Its growth during cooling predicts when atomic wave packets begin to overlap.
Magneto-optical trap: A device that uses laser light and magnetic-field gradients to capture and cool neutral atoms. It provides a standard starting point for preparing cold atomic samples.
Quantum coherence: The preservation of definite phase relationships between quantum states or alternatives. Coherence lets atomic waves produce stable, interpretable interference.
Gravimeter: An instrument that measures local gravitational acceleration. Atom interferometers can infer gravity from the phase accumulated by falling atomic waves.
Fermionic condensate: A low-temperature state in which fermions pair and acquire collective superfluid order. It demonstrates collective coherence in gases whose particles cannot share one state individually.
Classical gas: A gas whose particles are adequately described by classical statistical mechanics rather than quantum statistics. It contrasts with ultracold gases where indistinguishability changes measurable behavior.