Reviewed by Lexie CornerNov 21 2024
In a new study published in Nature Physics, a research team led by Dominik Schneble, Ph.D., a Professor in the Department of Physics and Astronomy, discovered a novel regime for cooperative radiative phenomena. This discovery offers new insights into a 70-year-old quantum optics problem. The study is supported by a theoretical paper published in Physical Review Research.
Representation of an array of matter-wave emitters held in an optical lattice tube (atomic excitations in red, emitted matter waves in blue, and effective vacuum coupling in green), along with data for directional superradiant emission. Image Credit: Alfonso Lanuza
A single photon of electromagnetic radiation is spontaneously emitted when an excited atom transitions to a lower-energy state, a process known as spontaneous emission. When one excited atom decays and emits a photon, the likelihood of finding the atom in its excited state decreases exponentially until it reaches zero.
In 1954, Princeton scientist R. H. Dicke investigated what occurs when a second, unexcited atom is introduced nearby. He proposed that the likelihood of detecting an excited atom would unexpectedly drop to one-half.
The excited system can be described by two simultaneous scenarios: one where the atoms are in phase, leading to enhanced emission (superradiance), and one where they are out of phase, resulting in suppressed emission (subradiance). When both atoms are initially excited, the decay always becomes superradiant.
Schneble and colleagues used ultracold atoms in a one-dimensional optical lattice to create arrays of synthetic quantum emitters that decay by emitting slow atomic matter waves. Unlike traditional systems, which emit photons traveling at the speed of light, this setup allowed them to study collective radiative phenomena under new conditions.
The researchers demonstrated directional collective emission and investigated the interplay between retardation and super- and subradiant dynamics by creating and controlling arrays of emitters with weakly and strongly interacting many-body excitation phases.
Dicke’s ideas are of great significance in quantum information science and technology (QIST). For example, there are intense efforts to harness super- and subradiance in arrays of quantum emitters coupled to one-dimensional waveguides. In our work, we are able to prepare and manipulate subradiant states with unprecedented control. We can shut off spontaneous emission and observe where the radiation hides in the array. To our knowledge, this is a first such demonstration.
Dominik Schneble, Ph.D., Professor, Department of Physics and Astronomy, Stone Brook University
Schneble is also a member of Stony Brook’s Center for Distributed Quantum Processing (CDQP).
The Stony Brook team, consisting of former Ph.D. students Youngshin Kim and Alfonso Lanuza, conducted research that provides new insights into significant concepts in quantum optics.
Schneble explains that, in Dicke’s hypothesis, photons do not play an active role because they travel quickly between nearby emitters on the decay timescale. However, there are exceptions to this assumption, such as in the channel of a long-distance quantum network, where a guided photon escaping from a decaying emitter may take a long time to reach the next emitter.
The researchers were able to explore this previously uncharted territory because the matter waves emitted in their system are billions of times slower than photons.
We see how collective decay from a superradiant state containing a single excitation takes time to form. It only happens once neighboring emitters have been able to communicate.
Youngshin Kim, Study Co-Author and Former Ph.D. Student, Stone Brook University
The team notes that tracking slow radiation in a system of emitters presents a significant theoretical challenge.
Co-author Lanuza compares this task to a complex game of catch and release.
A photon emitted by an atom can be caught back a few times before escaping or even be bound to the atom. The rules of the game become complicated when multiple atoms and photons participate – atoms exchanging photons, photons bouncing off excited atoms, and photons getting trapped between atoms are just a few of the processes involved.
Alfonso Lanuza, Study Co-Author and Former Ph.D. Student, Stone Brook University
Despite the complex photon-atom interaction, he was able to find mathematical solutions for two emitters with up to two excitations and arbitrary vacuum coupling. This part of the study could lead to the discovery of further complex or unexpected collective atomic decay processes in future investigations.
Schneble concluded, “Overall, our results on collective radiative dynamics establish ultracold matter waves as a versatile tool for studying many-body quantum optics in spatially extended and ordered systems.”
The National Science Foundation provided funding for the study, which also received support from Stony Brook’s CDQP.
Journal Reference:
Kim, Y. et. al. (2024) Super- and subradiant dynamics of quantum emitters mediated by atomic matter waves. Nature Physics. doi.org/10.1038/s41567-024-02676-w