We report the fabrication of a 1.2 cm long cavity directly on a nanofiber using femtosecond laser ablation. The cavity modes with finesse values in the range of 200-400 can enable the "strong-coupling" regime of cavity QED, with high cooperativity of 10-20, for a single atom trapped 200 nm away from the fiber surface [Phys. Rev. A80, 053826 (2009)PLRAAN1050-294710.1103/PhysRevA.80.053826]. Such cavity modes can still maintain the transmission between 40%-60%, suggesting a one-pass intracavity transmission of 99.53%. Other cavity modes, which can enable cooperativity in the range of 3-10, show transmission over 60%-85% and are suitable for fiber-based single-photon sources and quantum nonlinear optics in the "Purcell" regime.

We demonstrate a method for making precise measurements of the diameter of a tapered optical fiber with a sub-wavelength diameter waist (an optical nanofiber). The essence of the method is to create a composite photonic crystal cavity by mounting a defect-mode grating on an optical nanofiber. The resultant cavity has a resonance wavelength that is sensitive to the nanofiber's diameter, allowing the diameter to be inferred from optical measurements. This method offers a precise, nondestructive, and in situ way to characterize the nanofiber diameter.

We demonstrate an optical tweezer based single atom trapping on an optical nanofiber cavity. We show that the fluorescence of single atoms trapped on the nanofiber cavity can be readily observed in real-time through the fiber guided modes. The photon correlation measurements further clarify the atom number and the dynamics of the trap. The trap lifetime is measured to be 52±5 ms. From the photon statistics measured for different cavity decay rates, the effective coupling rate of the atom-cavity interface is estimated to be 34±2 MHz. This yields a cooperativity of 5.4±0.6 and a cavity enhanced channeling efficiency of 85±2% for a cavity mode having a linewidth of 164 MHz.These results may open new possibilities for building trapped single atom based quantum interfaces on an all-fiber platform.Realizing an efficient quantum interface will enable deterministic control and readout of the quantum states for quantum information processing [1]. In this context, atomic qubits offer unique capabilities for long coherence time and optical interfacing [1,2]. A recent trend towards optical interfacing is to combine the atomic qubits with nanophotonic platforms and develop hybrid quantum systems, where efficient quantum state-transfer between atoms and photons can be realized.Adiabatically tapered single mode optical fiber with subwavelength diameter waist, referred to as optical nanofiber (ONF), provides a unique fiber-in-line platform for quantum photonics applications [3,4]. The transverse confinement of photonic modes in the ONF has enabled new possibilities for manipulating atom-photon interactions [3][4][5][6]. Furthermore, it has been demonstrated that thousands of atoms can be trapped in the vicinity of the ONF by using guided light in a two-color dipole trap scheme [7][8][9]. This inherently leads to a fiber-in-line optically dense platform for quantum non-linear optics with an ensemble of atoms [10,11].On the other hand, for achieving non-linearity at single atom level, the coupling between the atom and the ONF guided modes can be substantially improved by introducing an in-line fiber cavity. Due to the strong transverse confinement of ONF guided modes, one can achieve strong-coupling regime of cavity quantum electrodynamics (QED) and high single atom cooperativity even for a moderate finesse ONF cavity [12]. A detailed review of various types of ONF cavities, can be found in Ref. [4]. Recently, strong-coupling between a trapped single atom and an ONF cavity has been demonstrated [13]. However, the widely adopted scheme of two-color guided mode trapping of atoms on the ONF [7][8][9][10][11]13], is the only scheme so far and it lacks the control over individual atoms. Preparation of quantum emitters on the ONF cavity, in a bottom-up approach using atomby-atom control may open new possibilities to engineer complex quantum systems. Therefore, development of new trapping schemes for atom-ONF interface is essential.Here, we demonstrate an optical tweezer based sideillumination trapping scheme to trap and interface indi-O...

We study the generation of correlated photon pairs and heralded single photons via strongly non-degenerate spontaneous four-wave mixing (SFWM) in a series of identical micro-/nano fibers (MNF). Joint spectral intensity of the biphoton field generated at the wavelength of about 880 nm and 1310 nm has been measured under excitation by 100 ps laser pulses demonstrating good agreement with the theoretical prediction. The measured zero-time second-order autocorrelation function was about 0.2 when the emission rate of the heralded photons was of 4 Hz. The MNFbased source perfectly matches standard single-mode fibers, which makes it compatible with the existing fiber communication networks. In addition, SFWM observation in a series of identical MNFs allows increasing generation rate of single photons via spatial multiplexing.

No abstract