Abstract The spin of light in subwavelength-diameter waveguides can be orthogonal to the propagation direction photons because strong transverse confinement. This changes sign when is reversed. Using this effect, we demonstrate directional spontaneous emission by laser-trapped caesium atoms into an optical nanofibre and control their excited state atomic emitters. In particular, tune counter-propagating guided modes from symmetric strongly asymmetric, where more than "Equation missing"<!--...

The realization of nanophotonic optical isolators with high isolation even at ultralow light levels and low losses is an open problem. Here, we employ the link between local polarization strongly confined its direction propagation to realize low-loss nonreciprocal transmission through a silica nanofiber single-photon level. resulting isolator controlled by spin state cold atoms. We perform our experiment in two qualitatively different regimes, i.e., ensemble atoms where each atom weakly...

Quantum simulation can provide insight into physical systems that are too complex for traditional computing techniques. A new proposal describes how a quantum simulator could be realized using laser-trapped circular Rydberg atoms, whose long lifetimes and stability beneficial simulations lasting up to seconds.

Fock states with photon numbers $n$ up to 7 are prepared on demand in a microwave superconducting cavity by quantum feedback procedure that reverses decoherence-induced jumps. Circular Rydberg atoms used as nondemolition sensors or single-photon emitter absorber actuators. The nature of these actuators matches the correction jumps due relaxation. flexibility this method is suited generation arbitrary sequences states.

We have frozen the coherent evolution of a field in cavity by repeated measurements its photon number. use circular Rydberg atoms dispersively coupled to mode for an absorption-free counting. These inhibit growth injected classical source. This manifestation quantum Zeno effect illustrates backaction number determination onto phase. The residual can be seen as random walk amplitude two-dimensional phase space. experiment sheds light measurement process and opens perspectives active feedback.

We analyze the quantum Zeno dynamics that takes place when a field stored in cavity undergoes frequent interactions with atoms. show repeated measurements or unitary operations performed on atoms probing state confine evolution to tailored subspaces of total Hilbert space. This confinement leads non-trivial evolutions and generation interesting non-classical states, including mesoscopic superpositions. elucidate main features mechanism context state-of-the-art electrodynamics experiment. A...

We experimentally study the ground state coherence properties of cesium atoms in a nanofiber-based two-color dipole trap, localized 200 nm away from fiber surface. Using microwave radiation to coherently drive clock transition, we record Ramsey fringes as well spin echo signals and infer reversible dephasing time $T_2^\ast=0.6$ ms an irreversible $T_2^\prime=3.7$ ms. By theoretically modelling signals, find that, for our experimental parameters, $T_2^\ast$ $T_2^\prime$ are limited by finite...

Tapered optical fibers with a nanofiber waist are versatile tools for interfacing light and matter. In this context, laser-cooled atoms trapped in the evanescent field surrounding of particular interest: They exhibit both long ground-state coherence times efficient coupling to fiber-guided fields. Here, we demonstrate electromagnetically induced transparency, slow light, storage pulses an ensemble cold nanofiber-based lattice. We measure slow-down group velocities 50 m/s. Moreover, store at...

The relaxation of a quantum field stored in high-$Q$ superconducting cavity is monitored by nonresonant Rydberg atoms. field, subjected to repetitive nondemolition photon counting, undergoes jumps between number states. We select ensembles realizations evolving from given Fock state and reconstruct the subsequent evolution their distributions. realize this way tomography process yielding all jump rates damping $n$ states ($0\ensuremath{\le}n\ensuremath{\le}7$) are found increase linearly...

We discuss an implementation of quantum Zeno dynamics in a cavity electrodynamics experiment. By performing repeated unitary operations on atoms coupled to the field, we restrict field evolution chosen subspaces total Hilbert space. This procedure leads promising methods for tailoring nonclassical states. propose realize "tweezers" picking coherent at point phase space and moving it towards arbitrary final position without affecting other nonoverlapping components. These effects could be...

Rydberg atoms are remarkable tools for quantum simulation and computation. They the focus of an intense experimental activity, mainly based on low-angular-momentum states. Unfortunately, atomic motion levels lifetime limit timescale to about 100 μs. Here, we demonstrate two-dimensional laser trapping long-lived circular states up 10 ms. Our method is very general opens many opportunities technologies with atoms. The ms time corresponds thousands interaction cycles in a circular-state-based...

Circular Rydberg atoms (CRAs), i.e., with maximal orbital momentum, are highly promising for quantum computation, simulation and sensing. They combine long natural lifetimes strong inter-atomic interactions coupling to electromagnetic fields. Trapping individual CRAs is essential harness these unique features. We report the first demonstration of laser-trapping in a programmable array optical bottle beams. observe decay trapped Rubidium circular level over 5ms using novel detection method....

The interaction of a two-level system (TLS) with single bosonic mode (BM) is one the most fundamental processes in quantum optics. Microscopically, it described by Rabi model (QRM). Here we propose versatile implementation this based on trapped cold atoms. Assuming realistic experimental conditions, show that our approach not restricted to Jaynes-Cummings regime but also allows exploring regimes ultrastrong coupling, deep strong and dispersive coupling. In contrast other QRM platforms, all...

Rydberg atoms are remarkable tools for the quantum simulation of spin arrays. Circular open way to simulations over very long time scales, using a combination laser trapping and spontaneous-emission inhibition, as shown in proposal XXZ spin-array simulator based on chains trapped circular [T.L. Nguyen $\textit{et al.}$, Phys. Rev. X 8, 011032 (2018)]. Such simulators could reach regimes (thermalization, glassy dynamics) that out those ordinary, low-angular-momentum short-lived atoms. Over...

A strongly confined light field necessarily exhibits a local polarization that varies on subwavelength scale. We demonstrate single optical mode of this kind can be used to selectively and simultaneously manipulate atomic ensembles are less than micron away from each other equally coupled the field. The technique is implemented with an nanofiber provides evanescent interface between guided two diametric linear arrays cesium atoms. Using mode, optically pumped opposite Zeeman states....

The ubiquitous decoherence phenomenon is responsible for the lack of quantum superpositions at macroscopic scale. It increasingly difficult to isolate a system from its environment when size increases. Making use weird properties mesoscopic states thus requires efficient means combat decoherence. One option real-time feedback. features components conventional feedback: measurement system's state (sensor), analysis (controller), and feedback action (actuator) aiming target state. random...

Circular Rydberg atoms (CRAs), i.e., with maximal orbital momentum, ideally combine long coherence times and strong interactions, a key property of quantum systems, in particular for the development technologies. However, dipole-dipole interaction between CRAs has not been observed so far. We report measurement characterization resonant two CRAs, individually trapped optical tweezers, find excellent agreement theoretical predictions. demonstrate dynamic control over strength by tuning...

An experimental investigation of the properties light backscattered by an array Cs atoms trapped evanescent field from a nanofiber shows that power and polarization depend on nanofiber-guided excitation in way significantly deviates previous predictions.

We present a method for reconstructing the average evolution of photon number distribution field decaying in high-Q cavity. It applies an iterative maximum likelihood state reconstruction algorithm to diagonal elements density operator. is based on quantum non-demolition measurements carried out with atoms crossing cavity one by one. A small set successively detected defines positive operator valued measure (POVM). The performed applying this POVM large ensemble realizations. An optimal...

This work considers the theory underlying a discrete-time quantum filter recently used in feedback experiment. It proves that this taking into account decoherence and measurement errors is optimal stable. We present general framework show it corresponds to recursive expression of least-square estimation density operator presence imperfections. By imperfections, we mean very sense unread performed by environment (decoherence) active non-ideal detectors. However, assume know precisely all...