Superconducting acousto-optic phase modulator.

We report the development of a superconducting acousto-optic phase modulator fabricated on a lithium niobate substrate. A titanium-diffused optical waveguide is placed in a surface acoustic wave resonator, where the electrodes for mirrors and an interdigitated transducer are made of a superconducting niobium titanium nitride thin film. The device performance is evaluated as a substitute for the current electro-optic modulators, with the same fiber coupling scheme and comparable device size.

Entanglement-based single-shot detection of a single magnon with a superconducting qubit.

The recent development of hybrid systems based on superconducting circuits provides the possibility of engineering quantum sensors that exploit different degrees of freedom. Quantum magnonics, which aims to control and read out quanta of collective spin excitations in magnetically ordered systems, provides opportunities for advances in both the study of magnetism and the development of quantum technologies. Using a superconducting qubit as a quantum sensor, we report the detection of a single magnon in a millimeter-sized ferrimagnetic crystal with a quantum efficiency of up to 0.

Studies on NMR-signal up-conversion from radio-frequency to optical regimes using a lightweight nanomembrane transducer.

Our recent report on Electro-Mechano-Optical (EMO) NMR proved the feasibility of up-conversion of NMR signals from radio-frequency to optical regimes using a metal-coated, high-Q membrane oscillator (Takeda et al., 2018). However, the signal-to-noise ratio, which can in principle exceed that of the conventional electrical detection scheme, was far below than ideal.

QUANTUM INFORMATION. Coherent coupling between a ferromagnetic magnon and a superconducting qubit.

Rigidity of an ordered phase in condensed matter results in collective excitation modes spatially extending to macroscopic dimensions. A magnon is a quantum of such collective excitation modes in ordered spin systems. Here, we demonstrate the coherent coupling between a single-magnon excitation in a millimeter-sized ferromagnetic sphere and a superconducting qubit, with the interaction mediated by the virtual photon excitation in a microwave cavity.

Hybridizing ferromagnetic magnons and microwave photons in the quantum limit.

We demonstrate large normal-mode splitting between a magnetostatic mode (the Kittel mode) in a ferromagnetic sphere of yttrium iron garnet and a microwave cavity mode. Strong coupling is achieved in the quantum regime where the average number of thermally or externally excited magnons and photons is less than one. We also confirm that the coupling strength is proportional to the square root of the number of spins.

Observation of a topological and parity-dependent phase of m = 0 spin states.

A Ramsey interrogation scheme was used to measure the phase shift of laser-cooled 87Rb clock-transition pseudospins arising as a result of a reversal of a bias-magnetic field, i.e., B--> -B, during the interrogation.

Observation of antinormally ordered Hanbury Brown-Twiss correlations.

We have measured antinormally ordered Hanbury Brown-Twiss correlations for coherent states of the electromagnetic field by using a stimulated parametric down-conversion process. Photons were detected by stimulated emission, rather than by absorption, so that the detection responded not only to actual photons but also to zero-point fluctuations via spontaneous emission. The observed correlations were distinct from normally ordered ones as they showed excess positive correlations, i.