Unit Posts

We present a magnetic trapping scheme for cold Rb-87 atoms based on light-induced fictitious magnetic fields generated by the evanescent field of an optical nanofiber (ONF) integrated with optical tweezers. We calculate and compare the trapping potentials for both Gaussian and Laguerre-Gaussian modes of the tweezer beam, combined with a quasilinearly polarized ONF-guided field. Based on the optical powers in the tweezer and ONF modes, we analyze the trap depths and the positions of the potential minima from the nanofiber surface. We show that, by varying the optical powers in the two fields, the trap position can be tuned over several hundred nanometers while simultaneously influencing the trap depth and trap frequencies. Such control over the atom-surface position is essential for studying distance-dependent effects on atoms trapped near a dielectric surface and optimizing atom-photon interfaces for quantum technology applications.

Precise positioning of quantum emitters is essential for next-generation photonic technologies, yet conventional free-space optical trapping methods require high laser powers that damage sensitive nanoparticles through heating. Here, ultralow-power trapping of biocompatible molecular graphene quantum dots (GQDs) is demonstrated using metamaterial plasmonic tweezers, achieving record-high normalized trap stiffness values at low intensities. Custom 19-nm molecular GQDs containing twisted double[7]carbohelicene (D7H) molecular cores are synthesized and their trapping dynamics are systematically investigated across dual hotspot types in the metamaterial array. The results establish safe operating regimes for heat-sensitive quantum emitters and reveal the fundamental interplay between optical and thermal forces in plasmonic trapping systems. This platform enables efficient nanopositioning of quantum emitters in ordered arrays while maintaining biocompatibility and photostability, opening pathways toward scalable single-photon source architectures and bioimaging applications.

Chaotic microcavities play a crucial role in several research areas, including the study of unidirectional microlasers, nonlinear optics, sensing, quantum chaos, and non-Hermitian physics. To date, most theoretical and experimental explorations have focused on two-dimensional (2D) chaotic dielectric microcavities, but there have been minimal studies on three-dimensional (3D) ones because precise geometrical information of a 3D microcavity can be difficult to obtain. Here, we image 3D microcavities with submicron resolution using X-ray microcomputed tomography (μCT), enabling nondestructive imaging that preserves the sample for subsequent use. By analyzing the ray dynamics of a typical deformed microsphere, we demonstrate that a sufficient deformation along all three dimensions can lead to chaotic ray trajectories over extended time scales. Notably, using the X-ray μCT reconstruction results, the phase space chaotic ray dynamics of a deformed microsphere are accurately established. X-ray μCT could become a unique platform for the characterization of such deformed 3D microcavities by providing a precise means for determining the degree of deformation necessary for potential applications in ray chaos and quantum chaos.

A promising platform for quantum information research relies on cavity coupled atomic spin-waves, enabling efficient operations such as quantum memories, quantum light generation and entanglement distribution. In this work, we study the strong coupling between non-classical collective spin excitations generated by Raman scattering in a cold Rb atomic ensemble, and a single cavity mode. We report on an intracavity spin wave to single photon conversion efficiency in the quantum domain, as evidenced by a violation of the Cauchy–Schwarz inequality. Our work establishes a relationship between the retrieval of an atomic spin wave in the non-classical regime and the vacuum Rabi splitting. We show that this relationship emerges within the efficiency spectrum, and we finally provide the optimal operational conditions to achieve the maximum intrinsic retrieval efficiency. Our data is well reproduced by simulations based on optical Bloch equations. This work deepens the understanding of cavity-enhanced spin wave readout and its potential applications.

 

 

Welcome to five new interns - Anton, Stephy, Kateryna, Nino, and Yueqian.

Dr Rohit Kumar (formerly IIT Patna, India) and Dr Lekshmi Eswaramoorthy (formerly IIT Bombay, India and Monash University, Australia) have recently joined the unit as postdocs.   

OIST is part of a 5 year bi-national research project between Japan and Germany focused on developing diamond-based quantum science and technology as an JST ASPIRE & DFG project.