The discrete nature of photons that are emitted from individual atoms ensures low fluctuations in brightness, as only one photon is emitted at a time. Scientists believe this property could be useful in developing future quantum technologies where low fluctuations will be important. Consequently, there is increased interest in building “artificial atoms” — engineered systems that act like atoms when they emit light, but whose properties are more easily tailored. The presence of vibrations in these artificial atoms, which are much larger than natural atoms, is unavoidable and usually considered to be detrimental. However, a research team led by the University of Bristol has established that the vibrations occurring in artificial atoms can help suppress fluctuations in brightness, leading to even stronger suppression than what occurs in natural atomic systems. The team showed that the low fluctuations in brightness present in “artificial atoms” could be used to build more accurate quantum sensors. Atomistic structure of an artificial atom that could be used to produce light with vibrationally suppressed fluctuations for quantum-enhanced sensors. Courtesy of G. Klimeck et al. (2011), “Self-Assembled Quantum Dot Wave Structure,” https://nanohub.org/resources/10689, under license: https://creativecommons.org/licenses/by-nc-sa/3.0/. The researchers showed that vibrational interactions could be harnessed to generate optical states with a higher degree of quadrature squeezing than in isolated atomic systems. Using the example of a driven quantum dot coupled to phonons, they demonstrated that it is feasible to surpass the maximum level of squeezing theoretically obtainable in an isolated atomic system and come close to saturating the fundamental upper bound on squeezing from a two-level emitter. They analyzed the performance of these vibrationally enhanced squeezed states in a phase estimation protocol and found that for the same photon flux, the vibrationally enhanced squeezed state could outperform the single mode squeezed vacuum state. Principal investigator Dara McCutcheon said that at low temperatures the vibrational environment acts to cool the system, in a sense “freezing” the energy levels. This, in turn, suppresses the fluctuations on the emitted photons. The work could point toward a new vision for artificial atoms, in which their solid-state nature is put to good use to produce light that could not be made using natural atomic systems. The research also could lead to applications that use artificial atoms for quantum-enhanced sensing, ranging from small-scale magnetometry that could be used to measure signals in the brain all the way up to full-scale gravitational wave detection. The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-10909-3).