Waves in Rydberg Plasmas

José Tito Mendonça, Hugo Terças

Ruoxi Wang, John Sous, M. Aghigh +5 more

Out-of-equilibrium, strong correlation in a many-body system can trigger emergent properties that act to constrain the natural dissipation of energy and matter. Signs of such self-organization appear in the avalanche, bifurcation, and quench of a state-selected Rydberg gas of nitric oxide to form an ultracold, strongly correlated ultracold plasma. Work reported here focuses on the initial stages of avalanche and quench and uses the mm-wave spectroscopy of an embedded quantum probe to characterize the intermolecular interaction dynamics associated with the evolution to plasma. Double-resonance excitation prepares a Rydberg gas of nitric oxide composed of a single selected state of principal quantum number, n0. Penning ionization, followed by an avalanche of electron–Rydberg collisions, forms a plasma of NO+ ions and weakly bound electrons, in which a residual population of n0 Rydberg molecules evolves to a state of high orbital angular momentum, ℓ. Predissociation depletes the plasma of low-ℓ molecules. Relaxation ceases and n0ℓ(2) molecules with ℓ ≥ 4 persist for very long times. At short times, varying excitation spectra of mm-wave Rydberg–Rydberg transitions mark the rate of electron-collisional ℓ-mixing. Deep depletion resonances that persist for long times signal energy redistribution in the basis of central-field Rydberg states. The widths and asymmetries of Fano line shapes witness the degree to which coupling in the arrested bath (i) broadens the allowed transition and (ii) mixes the local network of levels in the ensemble.

José Tito Mendonça, John Gideon Hartnett, Paul C Abbott

Here we discuss collective processes and plasma effects that can be found in ultra‐cold matter. First, we consider the ultra‐cold atomic gas that can be produced in a magneto‐optical trap. Due to the existence of long‐range repulsive forces, new collective oscillation can take place, resembling sound waves but with a cut‐off frequency. We also examine new phenomena in Rydberg plasmas, resulting from laser ionization of the ultra‐cold gas. In these very low temperature plasmas a large amount of excited Rydberg states can exist, leading to a new dispersion relation for the electromagnetic waves. Enhanced magnetic field generation will also be considered. Finally, we discuss the collective properties of Bose Einstein condensates, showing a strong analogy with collective plasma processes. Two related examples are given as an illustration: Bogoliubov oscillations in the condensate, and two‐stream instabilities of counter‐streaming BECs.

Raymond Flannery

Thomas Pattard, Thomas Pohl, Jan Michael Rost

Fernanda B. V. Martins, James S. Keller, Edward R. Grant

Resonant mm-wave fields drive n0f(2)→(n0±1)g(2) transitions in a state-selected n0f(2) Rydberg gas of NO. This transformation produces a clear signature in the selected field ionisation spectrum and dramatically increases the intensity of corresponding features in the spectrum of the n0f(2) Rydberg series observed in UV–UV double resonant transitions via the A 2Σ+, N′=0 state. Here, n0 refers to the principal quantum number of an f Rydberg state converging to the N+=2 rotational state of NO+X 1Σ+. Enhancement owing to transitions from ℓ=3 (f) to ℓ=4 (g) appears both in the electron signal detected at early time by the field ionisation of Rydberg molecules and, 40μs later, as the late-peak signal of plasma in a state of arrested relaxation. Similar stabilisation and enhanced intensity also occurs for shorter-lived interloping complex resonances, 44p(0)−43d(1) and 43p(0)−42d(1). We conclude from these observations that avalanche alone does not guarantee a plasma state of arrested relaxation. But rather, the formation of an arrested phase requires both avalanche-produced NO+ ions and a persistent population of long-lived Rydberg molecules.