Quantum Engineering with Optical Fibers
Enhancing fiber atom interferometer by in-fiber laser cooling
We demonstrate an inertia sensitive atom interferometer optically guided inside a 22-cm-long negative curvature hollow-core photonic crystal fiber with an interferometer time of 20 ms. The result improves the previous fiber guided atom interferometer sensitivity by three orders of magnitude. The improvement arises from the realization of in-fiber -enhanced gray molasses and delta-kick cooling to cool atoms from 32 μK to below 1μK in 4 ms. The in-fiber cooling overcomes the inevitable heating during the atom loading process and allows a shallow guiding optical potential to minimize decoherence. Our results permit bringing atoms close to source fields for sensing and could lead to compact inertial quantum sensors with a submillimeter resolution.
Large array of Schrodinger cat states facilitated by an optical waveguide
Quantum engineering using photonic structures offers new capabilities for atom-photon interactions for quantum optics and atomic physics, which could eventually lead to integrated quantum devices. Despite the rapid progress in the variety of structures, coherent manipulation of the quantum states of single atoms with photonic modes at the single quanta level has yet to be demonstrated. Here, we use the waveguide mode of a hollow-core photonic crystal fibre to manipulate the mechanical Fock states of single atoms in a harmonic potential inside the fibre. We create a large array of Schrödinger cat states, a quintessential feature of quantum physics and a key element in quantum information processing and metrology, of approximately 15000 atoms along the fibre by entangling the electronic states with the coherent harmonic oscillator states of single atoms. Our results demonstrate the first coherent quantum control of the atoms with the photonic structure and provide an essential step for quantum information and simulation with a wide range of photonic waveguide systems.
Long light storage time in an optical fiber
Phys. Rev. Research 2, 033320 – Published 27 August 2020.
Light storage in an optical fiber is an attractive component in quantum optical delay line technologies. Although silica-core optical fibers are excellent in transmitting broadband optical signals, it is challenging to tailor their dispersive property to slow down light pulses or store it in the silica-core for long delay time. Coupling dispersive and coherent medium with an optical fiber is promising in supporting long optical delay. Here, we load cold Rb atomic vapor into an optical trap inside a hollow-core photonic crystal fiber, and store the phase of the light in a long-lived spin-wave formed by atoms and retrieve it after a fully controllable delay time using electromagnetically-induced-transparency (EIT). We achieve over 50 ms of storage time and the result is equivalent to 8.7×10^-5 dB/μs of propagation loss in the conventional fiber. Our demonstration could be used for buffering and regulating classical and quantum information between remote networks.
Transporting long-lived quantum spin coherence in a photonic crystal fiber
Confining particles in hollow-core photonic crystal fibers has opened up new prospects to scale up the distance and time over which particles can be made to interact with light. However, maintaining long-lived quantum spin coherence and/or transporting it over macroscopic distances in a waveguide remain challenging. Here, we demonstrate coherent guiding of ground-state superpositions of 85Rb atoms over a range of one centimeter and hundreds of miliseconds inside a hollow-core photonic crystal fiber. The decoherence is mainly due to dephasing from the residual differential light shift from the optical trap and the inhomogeneity of an ambient magnetic field. Our experiment establishes an important step towards a versatile platform that can lead to applications in quantum information networks and a matter wave circuit for quantum sensing.
An atom interferometer inside a hollow-core photonic crystal fiber
Coherent interactions between electromagnetic and matter waves lie at the heart of quantum science and technology. However, the diffraction nature of light has limited the scalability of many atom-light-based quantum systems. We use the optical fields in a hollow-core photonic crystal fiber to spatially split, reflect, and recombine a coherent superposition state of free-falling 85Rb atoms to realize an intertia-sensitive atom interferometer. The interferometer operates over a diffraction-free distance, and the contrasts and phase shifts at different distances agree within one standard error. The integration of phase coherent photonic and quantum systems here shows great promise to advance the capability of atom interferometers in the field of precision measurement and quantum sensing, with miniature design of apparatus and high efficiency of laser power consumption.