arXiv subjects

Andrei H. Gheorghe

Publications and source records attributed to Andrei H. Gheorghe.

2 recordsLinked to original sources

arXiv2019

Direct observation of bimolecular reactions of ultracold KRb molecules

Femtochemistry techniques have been instrumental in accessing the short time scales necessary to probe transient intermediates in chemical reactions. Here we take the contrasting approach of prolonging the lifetime of an intermediate by preparing reactant molecules in their lowest ro-vibronic quantum state at ultralow temperatures, thereby drastically reducing the number of exit channels accessible upon their mutual collision. Using ionization spectroscopy and velocity-map imaging of a trapped gas of potassium-rubidium molecules at a temperature of 500~nK, we directly observe reactants, intermediates, and products of the reaction $^{40}$K$^{87}$Rb + $^{40}$K$^{87}$Rb $\rightarrow$ K$_2$Rb$^*_2$ $\rightarrow$ K$_2$ + Rb$_2$. Beyond observation of a long-lived energy-rich intermediate complex, this technique opens the door to further studies of quantum-state resolved reaction dynamics in the ultracold regime.

physics.atom-ph↗

arXiv2014

Covert Optical Communication

Encryption prevents unauthorized decoding, but does not ensure stealth---a security demand that a mere presence of a message be undetectable. We characterize the ultimate limit of covert communication that is secure against the most powerful physically-permissible adversary. We show that, although it is impossible over a pure-loss channel, covert communication is attainable in the presence of any excess noise, such as a $300$K thermal blackbody. In this case, $\mathcal{O}(\sqrt{n})$ bits can be transmitted reliably and covertly in $n$ optical modes using standard optical communication equipment. The all-powerful adversary may intercept all transmitted photons not received by the intended receiver, and employ arbitrary quantum memory and measurements. Conversely, we show that this square root scaling cannot be outperformed. We corroborate our theory in a proof-of-concept experiment. We believe that our findings will enable practical realizations of covert communication and sensing, both for point-to-point and networked scenarios.

cs.IT↗