Optical spin-mechanics quantum interface: entanglement and back-action evasion

Research output: Book/ReportPh.D. thesisResearch

The experimental control of physical systems to their ultimate quantum limits has advanced tremendously in the last couple of decades. Parallel advancements in the theoretical descriptions allowed for better understanding the performance requirements needed for using quantum-enabled technologies in real world applications. With that, it has also become more and more clear that a single platform might not be able to realize all the protocols needed, for example, in a future quantum information processing network. Hybrid quantum devices attempt to combine fundamentally different systems with high efficiency, harnessing the advantages from its constituent elements. In this thesis, we report the recent developments on the hybrid interface between a mechanical oscillator prepared in dielectric membrane and a spinoscillator prepared in an atomic ensemble. The mechanical oscillator, a drumlike stressed silicon nitride membrane, is placed inside a high finesse cavity and mounted in a cryostat operating at 4 K. The spin oscillator is prepared in the ground state manifold of an optically pumped cesium vapor, placed in a homogeneous static magnetic field and confined in a glass vapor cell at approximately 330 K. Each subsystem is coupled to light, operating in the quantum back-action limited regime, that is, at the limit in which the measurement disturbs the dynamics of the oscillator significantly. The optical interface is established by coupling the systems in a cascaded fashion. We show that the measurement induced quantum back-action can be destructively interfered whenpreparing the spin ensemble in a effective negative mass regime . In the experiments, we show up to 4.6 dB reduction of the quantum back-action contribution. Furthermore, we show that the back-action evasion, along with the information acquired via the measurement, allows for preparing the hybrid system in an entangled continuous variables Einstein-Podolsky-Rosen-like state with variance below the inseparability limit, 0.83±0.03<1. The established quantum link constitutes a new milestone in the hybrid systems landscape and paves the road towards measurement of motion beyond the standard quantum limits of sensitivity, as well as towards teleportation-based protocols in hybrid quantum networks.
Original languageEnglish
PublisherNiels Bohr Institute, Faculty of Science, University of Copenhagen
Number of pages181
Publication statusPublished - 2020

ID: 251306015