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Koji Sakai

Publications and source records attributed to Koji Sakai.

2 recordsLinked to original sources

Optomechanical parametric control of mid-infrared photons via molecular vibrational polariton

Controlling mid-infrared (MIR) photons using well-developed telecom photonic platforms would enable new functionalities in molecular and quantum photonics. However, establishing efficient interactions between MIR and telecom photons remains challenging due to their large spectral separation and weak nonlinear coupling. Here, we demonstrate optomechanical control of MIR photons mediated by vibrational polaritons, enabling photon-photon interaction between MIR and telecom fields across distant spectral regions. Using a Fabry-Pérot cavity incorporating a vibrationally active polymer, we observe telecom-driven dissipation enhancement of MIR photons at 9.5 $μ$m with a modulation depth of 1% under a 4 mW pump. The linear power dependence, mixing-ratio dependence, and detuning response consistently indicate a MIR and telecom photon-photon conversion enabled by strong light-matter coupling. This approach establishes a polaritonic optomechanical platform for bridging disparate spectral regimes and provides a dissipation-engineered route toward hybrid MIR photonics and quantum transduction.

physics.optics

Magnetometry of neurons using a superconducting qubit

We demonstrate magnetometry of cultured neurons on a polymeric film using a superconducting flux qubit that works as a sensitive magnetometer in a microscale area. The neurons are cultured in Fe$^{3+}$ rich medium to increase magnetization signal generated by the electron spins originating from the ions. The magnetometry is performed by insulating the qubit device from the laden neurons with the polymeric film while keeping the distance between them around several micrometers. By changing temperature (12.5 - 200 mK) and a magnetic field (2.5 - 12.5 mT), we observe a clear magnetization signal from the neurons that is well above the control magnetometry of the polymeric film itself. From electron spin resonance (ESR) spectrum measured at 10 K, the magnetization signal is identified to originate from electron spins of iron ions in neurons. This technique to detect a bio-spin system can be extended to achieve ESR spectroscopy at the single-cell level, which will give the spectroscopic fingerprint of cells.

quant-ph