Here we demonstrate the experimental realization of a fiber-integrated optical circulator whose operation direction is controlled by the quantum state of a single atom. The device is based on a bottle whispering-gallery-mode microresonator interfaced by two optical nanofibers. Depending on its internal state, the single atom couples differently to the chiral resonator fields. This results in a direction dependent transmission through the resonator and thus realizes an optical circulator. The demonstrated quantum optical circulator opens new ways for routing and processing quantum information in optical circuits.
Here we demonstrate the experimental realization of a fiber-integrated optical circulator whose operation direction is controlled by the quantum state of a single atom. The device is based on a bottle whispering-gallery-mode microresonator interfaced by two optical nanofibers. Depending on its internal state, the single atom couples differently to the chiral resonator fields. This results in a direction dependent transmission through the resonator and thus realizes an optical circulator. The demonstrated quantum optical circulator opens new ways for routing and processing quantum information in optical circuits.
Integrated nonreciprocal optical components, which have an inherent asymmetry between their forward and backward propagation direction, are key for routing signals in photonic circuits. Here, we demonstrate a fiber-integrated quantum optical circulator operated by a single atom. Its nonreciprocal behavior arises from the chiral interaction between the atom and the transversally confined light. We demonstrate that the internal quantum state of the atom controls the operation direction of the circulator and that it features a strongly nonlinear response at the single-photon level. This enables, for example, photon number-dependent routing and novel quantum simulation protocols. Furthermore, such a circulator can in principle be prepared in a coherent superposition of its operational states and may become a key element for quantum information processing in scalable integrated optical circuits.
We demonstrate highly efficient switching of optical signals between two optical fibers controlled by a single atom. The key element of our experiment is a whispering-gallery-mode bottle microresonator, which is coupled to a single atom and interfaced by two tapered fiber couplers. This system reaches the strong coupling regime of cavity quantum electrodynamics, leading to a vacuum Rabi splitting in the excitation spectrum. We systematically investigate the switching efficiency of our system, i.e., the probability that the fiber-optical switch redirects the light into the desired output. We obtain a large redirection efficiency reaching a raw fidelity of more than 60% without postselection. Moreover, by measuring the second-order correlation functions of the output fields, we show that our switch exhibits a photon-number-dependent routing capability.
We demonstrate trapping of a single ^{85}Rb atom at a distance of about 200 nm from the surface of a whispering-gallery-mode bottle microresonator. The atom is trapped in an optical potential, which is created by retroreflecting a red-detuned focused laser beam from the resonator surface. We counteract the trap-induced light shift of the atomic transition frequency by superposing a second laser beam. This allows us to observe a vacuum Rabi splitting in the excitation spectrum of the coupled atom-resonator system. This first demonstration of stable and controlled interaction of a single atom with a whispering-gallery mode in the strong coupling regime opens up the route toward the implementation of quantum protocols and applications that harvest the chiral atom-light coupling present in this class of resonators.
Nanophotonic components allow the control of the flow of light in integrated optical environments. Thereby, the light’s strong confinement leads to an inherent link between its local polarization and propagation direction which fundamentally alters the physics of light-matter interaction and gives rise to phenomena such as directional emission and direction-dependent coupling strengths [1]. I will present the underlying principles of this chiral light-matter interaction and its consequences for integrated applications [1]. In particular, I will show how we employ this effect to control the direction of spontaneous emission [2] and to realize low-loss nonreciprocal transmission at the single-photon level through a silica nanofiber [3]. We use two different approaches where either an ensemble of spin-polarized atoms is weakly coupled to a nanofiber or a single atom is strongly coupled to the nanofiber via a whispering-gallery-mode resonator. The resulting optical isolators show a strong imbalance between the transmissions in forward and reverse direction and, at the same time, a forward transmissions exceeding 70%. We extended this system to a 4-port device, where a single atom routes photons nonreciprocally from one fiber port to the next. This realizes a quantum optical circulator [4] which can even be prepared in a superposition of its operational modes. The demonstrated systems exemplify a new class of (quantum) nanophotonic devices that are ideally suited for photonic quantum information processing and quantum simulation. [1] Nature 541, 473, (2017). [2] Science 346, 67 (2014). [3] Phys. Rev. X 5, 041036 (2015). [4] Science 354, 1577 (2016).
We demonstrate highly efficient switching of optical signals between two optical fibers controlled by a single atom.The key element of our experiment is a whispering-gallery-mode bottle microresonator, which is coupled to a single atom and interfaced by two tapered fiber couplers.This system reaches the strong coupling regime of cavity quantum electrodynamics, leading to a vacuum Rabi splitting in the excitation spectrum.We systematically investigate the switching efficiency of our system, i.e., the probability that the fiber-optical switch redirects the light into the desired output.We obtain a large redirection efficiency reaching a raw fidelity of more than 60% without postselection.Moreover, by measuring the second-order correlation functions of the output fields, we show that our switch exhibits a photon-number-dependent routing capability.
Summary form only given. Controlling the interaction of light and matter is the basis for diverse applications ranging from light technology to quantum information processing. Nowadays, many of these applications are based on nanophotonic structures. It turns out that the confinement of light in such nanostructures imposes an inherent link between its local polarization and its propagation direction, also referred to as spin-momentum locking of light [1]. Remarkably, this leads to chiral, i.e., propagation direction-dependent effects in the emission and absorption of light, and elementary processes of light-matter interaction are fundamentally altered. For example, when coupling plasmonic particles or atoms to evanescent fields, the intrinsic mirror symmetry of the particles' emission can be broken. In our group, we observed this effect in the interaction between single rubidium atoms and the evanescent part of a light field that is confined by continuous total internal reflection in a whispering-gallery-mode microresonator [2]. In the following, this allowed us to realize chiral nanophotonic interfaces in which the emission direction of light into the structure is controlled by the polarization of the excitation light [3] or by the internal quantum state of the emitter [4], respectively. Moreover, we employed this chiral interaction to demonstrate an integrated optical isolator [5] as well as an integrated optical circulator [6] which operate at the single-photon level and which exhibit low loss. The latter are the first two examples of a new class of nonreciprocal nanophotonic devices which exploit the chiral interaction between single quantum emitters and transversally confined photons.