住友電氣工業

We report the first experimental characterization of stimulated Raman scattering (SRS) in coupled-core multi-core fibers (MCFs). The experiment was performed using field-deployed fibers, with two complementary methodologies. First, the effective Raman gain coefficient was directly measured over a bandwidth of 120 nm – covering the upper S-, C- and lower L-bands – with the Raman pump being injected into different combinations of fiber cores and using either co- or counter-propagating signal. Second, we analyzed the spectral power tilt induced by SRS when transmitting a wavelength-division multiplexed signal spanning the entire C-band from 1529.4 nm to 1564.2 nm, which was found to be in agreement with the Raman gain coefficient measurements. Measurements performed on a co-deployed standard single-mode fiber (SMF) produced similar results. This observation, together with the notion that the Raman gain coefficient should be similar in MCFs and SMFs, validates our earlier derived model of SRS in fibers with strong mode mixing.

Abstract Nitrogen-vacancy (NV) center ensembles in diamond are one of the most promising solid-state quantum platforms for various sensing applications. Achieving ultimate sensitivity requires simultaneously long spin dephasing times ( $${T}_{2}^{* }$$ T 2 * ) and high NV center concentrations. In this work, we propose a systematic measurement approach to quantify the electron spin dephasing in NV center ensembles and analyze the contributions of various sources to the dephasing time, including NV-NV interactions, strain and electric field distributions, 13C nuclear spins, and P1 electron spins. Our method is validated using a series of high-performance diamond samples, providing a comprehensive understanding of dephasing mechanisms and revealing correlations between NV concentration and different dephasing sources. Building on these insights, we outline strategies to further enhance the achievable sensitivity for DC magnetic field measurements.

The integration of carbon nanotube (CNT) macroscopic assemblies into advanced electronics and energy systems requires precise control over both their nanoscale structure and bulk properties. Here, we present a halogen-assisted floating catalyst chemical vapor deposition (FC-CVD) strategy that enhances the electrical conductivity of single-walled CNT (SWCNT) films through the controlled introduction of halogen-containing organic precursors. Among the additives screened, bromine (Br) most effectively reduced the sheet resistance from similar to 5400 Omega/square to 139 Omega/square at 90% optical transmittance. Comprehensive structural characterization shows that an increase in CNT length is the primary origin of this conductivity enhancement. The use of Br additives in FC-CVD increased the CNT bundle length and the effective CNT length by factors of 2.7 and 7.6, respectively, which markedly reduced the density of inter-tube junctions and their associated contact resistance. Other structural factors, such as chirality distribution, bundle diameter, crystallinity, and doping effects, were found to have only minor influence. These results clarify the multifaceted role of halogen species in CNT growth chemistry and highlight how nanoscale structural design can be used to optimize macroscopic CNT assemblies for high-performance electronic and energy applications.

Originally envisioned as a solution for the capacity crunch in telecommunications networks, multicore fibers (MCFs) are contributing to scientific fields beyond telecom, such as sensing and metrology. Confined within the same cladding, the cores of MCF have a high degree of noise correlation, which can be harnessed for a variety of applications. Here, we investigate MCF as a solution to the challenging problem of quantum and classical light co-existence in phase-stabilized quantum networks by operating the quantum and stabilization light in separate but highly correlated cores of a 7-core MCF. Over 40 km of spooled fiber, we achieved 100 attosecond integrated jitter on one core by using phase information derived from another core. This allows for 100% duty cycle on a quantum channel while maintaining a low spurious photon rate from optical crosstalk. With cycle-slip-free stabilization over 6 hours, frequency detuning between designated stabilization and quantum channels, and an additional 40 dB rejection of noise photons provided by the low optical crosstalk between cores, we achieved a Raman scattering-induced spurious photon rate of only 0.01 photons/s in 100 GHz bandwidth. Our results with MCF demonstrate a promising approach to ultra-stable quantum networks with 100% duty cycle on the quantum channel.

Sub-picotesla level magnetometry has been demonstrated using negatively-charged nitrogen-vacancy (NV) centers in diamond by increasing the number of spins simultaneously used for sensing in an NV ensemble. However, such scale-up often introduces spatial inhomogeneities in detuning and control field amplitudes, which degrade sensitivity. Although several techniques have been utilized to overcome these challenges, including pulsed dynamical decoupling or shaped pulses, these are not generally compatible with the current state-of-the-art techniques for GHz-range AC magnetometry with NV ensembles, which are typically based on Rabi oscillations. In this work we experimentally demonstrate GHz-range AC magnetometry using a large ensemble of NV centers under spatially inhomogeneous drive fields by employing concatenated continuous dynamical decoupling, which is designed for robustness against such imperfections. We compare its performance with the conventional direct Rabi method and show that the robust dressed states in our method extend significantly the measuring range to weaker signals in GHz-range AC magnetometry.