We experimentally implement a system of cavity optomagnonics, where a sphere of ferromagnetic material supports whispering gallery modes (WGMs) for photons and the magnetostatic mode for magnons. We observe pronounced nonreciprocity and asymmetry in the sideband signals generated by the magnon-induced Brillouin scattering of light. The spin-orbit coupled nature of the WGM photons, their geometrical birefringence, and the time-reversal symmetry breaking in the magnon dynamics impose the angular-momentum selection rules in the scattering process and account for the observed phenomena. The unique features of the system may find interesting applications at the crossroad between quantum optics and spintronics.

We demonstrate cavity QED conditions in the Purcell regime for single quantum emitters on the surface of an optical nanofiber. The cavity is formed by combining an optical nanofiber and a nanofabricated grating to create a composite photonic crystal cavity. By using this technique, significant enhancement of the spontaneous emission rate into the nanofiber guided modes is observed for single quantum dots. Our results pave the way for enhanced on-fiber light-matter interfaces with clear applications to quantum networks.

We report the experimental observation of rectified momentum transport for a Bose-Einstein Condensate kicked at the Talbot time (quantum resonance) by an optical standing wave. Atoms are initially prepared in a superposition of the 0 and −2 k l momentum states using an optical π/2 pulse. By changing the relative phase of the superposed states, a momentum current in either direction along the standing wave may be produced. We offer an interpretation based on matter wave interference, showing that the observed effect is uniquely quantum.The current interest in rectified atomic diffusion, or atomic ratchets, may be traced back to fundamental thermodynamical concerns [1] and also the desire to understand the so-called "Brownian motors" linked to directed diffusion on a molecular scale [2,3]. Abstractly, the ratchet effect may be defined as the inducement of directed diffusion in a system subject to unbiased perturbations due to a broken spatio-temporal symmetry.Given the scale on which such microscopic ratchets must work, it is not surprising that the concept of quantum ratchets has recently augmented this area of investigation. The addition of quantum effects such as tunneling gives rise to new ratchet phenomena such as current reversal [4]. Whilst early quantum ratchet investigations, both theoretical and experimental, have focussed on the role of dissipative fluctuations in driving a ratchet current [5], recent theory has considered the possibility of Hamiltonian ratchets, where the diffusion arises from Hamiltonian chaos rather than stochastic fluctuations [6]. This has lead to proposals [7,8] and even an experimental realisation [9] for ratchet systems realised using atom optics, in the context of the atom optics kicked rotor [10] where periodic pulses from an optical standing wave kick atoms into different momentum states.It is generally accepted that a ratchet effect cannot be produced without breaking the spatio-temporal symmetry of the kicked rotor system. In Ref.[9], a rocking sine wave potential was combined with broken time symmetry of the kicking pulses to effectively realise such a system in an experiment. Other schemes involve the use of quantum resonance (QR) to drive the ratchet effect. At QR, atoms typically exhibit linear momentum growth symmetrical about the initial mean momentum. However it has been suggested that merely breaking the spatial symmetry of the kicked rotor at QR may be sufficient to produce a ratchet current [11]. In this letter we present the first experimental evidence of such a resonant ratchet effect in which the underlying mechanism is purely quantum. Our system uses a Bose-Einstein condensate (BEC) kicked by an optical standing wave [12], but there is no asymmetry in either the kicking potential * Electronic address: mark@ils.uec.ac.jp or the period of the kicks, (which is set to the Talbot time T T corresponding to quantum resonance [13]). Rather, the observed directed diffusion is a property of the initial atomic wavefunction (which we prepare before kicking) in the presenc...

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