Energizer atoms: Physicists find new way to keep atoms excited

The animation of JILA's experiment kept atoms excited longer than usual. Hanacek is aNIST.

JILA researchers have tricked nature by tuning a dense quantum gas of atoms to make a congested "Fermi sea," thus keeping atoms in a high-energy state, or excited, for about 10% longer than usual. The technique could be used to improve communication networks.

atoms that are excited above their resting state naturally calm down, or decay, by releasing light in quantized portions called photons. The glow of fireflies and emission from LEDs are examples of this common process. The rate of decay can be changed by altering the environment. The new work focuses on the atoms and modifies the environment.

The JILA method uses a rule of the quantum world known as the Pauli exclusion principle, which says that fermions can't share the same quantum states at the same time. If enough fermions are in a crowd, an excited fermion might not be able to fling out a photon as usual. The recoil could land it in the same state of motion as one of its neighbors, which is forbidden due to a mechanism called Pauli blocking.

Science describes the blocking achievement. The National Institute of Standards and Technology and the University of Colorado Boulder operate JILA.

NIST/JILA Fellow Jun Ye said that Pauli blocking uses well-organized quantum motional states of a Fermi sea to block the recoil of an atom that wants to decay. The control of matter's properties was previously deemed un changeable.

The animation shows atoms releasing light faster from a thermal gas. Hanacek is aNIST.

The JILA group is the first to actually do something about the idea of engineering an atom's excited-state lifetime by placing it in a Fermi sea. This is the first time that atoms' internal radiation properties have been linked to their external motion.

The JILA team carried out the experiments with a low-energy, or degenerate, Fermi gas of thousands of strontium atoms. The JILA group uses quantum gases to make atomic clocks. In these low-temperature Fermi gases, the atoms' properties are restricted to specific values, and the atoms avoid each other by keeping a minimum distance between pairs. atoms in ordinary gases are distributed randomly.

The researchers used blue light to excite atoms in the sea and then measured the resulting photon radiation. The team reduced photon emission by up to 50% by setting up specific conditions. An atom prepared in the excited state would stay in this state 10% longer than usual. The researchers used photon scattering as an indirect indicator because the excited lifetime was too short. Future experiments using different energy levels in the atoms or denser gases could extend excited states for longer time periods or even block decay entirely.

The experiment made a gas with the lowest possible energy, which allowed the blocking phenomenon to occur. The Fermi sea was large enough that atoms in the middle couldn't escape. The surface can't be easily blocked.

The researchers excited a small number of atoms and collected the emitted photons at a narrow angle. The configuration allowed for observation of small motion transfers. The blocking effect would be weakened if the atoms were given too much of a kick.

The JILA technique offers new ways to engineer atom-light systems, with potential applications such as protecting optical qubits in quantum communication networks and improving atomic clock stability by extending atom interrogation times.

Christian Sanner and his team are blocking of atom-light scattering. www.science.org/doi/10.1126/science.

Science journal information.

Physicists find a new way to keep atoms excited.

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