Polarization Dependent Scattering in Cavity Optomagnonics.

The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Because of the short cavity length, the longitudinal mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one sideband is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-film geometry. A copolarized scattering due to Cotton-Mouton effect is also observed. In addition, the magnon modes involved are identified as Damon-Eshbach surface modes, whose nonreciprocal propagation could be exploited in device applications. This Letter experimentally demonstrates the important role of second-order Cotton-Mouton effect for optomagnonic devices.

Fast Gate-Based Readout of Silicon Quantum Dots Using Josephson Parametric Amplification.

Spins in silicon quantum devices are promising candidates for large-scale quantum computing. Gate-based sensing of spin qubits offers a compact and scalable readout with high fidelity, however, further improvements in sensitivity are required to meet the fidelity thresholds and measurement timescales needed for the implementation of fast feedback in error correction protocols. Here, we combine radio-frequency gate-based sensing at 622 MHz with a Josephson parametric amplifier, that operates in the 500-800 MHz band, to reduce the integration time required to read the state of a silicon double quantum dot formed in a nanowire transistor. Based on our achieved signal-to-noise ratio, we estimate that singlet-triplet single-shot readout with an average fidelity of 99.7% could be performed in 1 µs, well below the requirements for fault-tolerant readout and 30 times faster than without the Josephson parametric amplifier. Additionally, the Josephson parametric amplifier allows operation at a lower radio-frequency power while maintaining identical signal-to-noise ratio. We determine a noise temperature of 200 mK with a contribution from the Josephson parametric amplifier (25%), cryogenic amplifier (25%) and the resonator (50%), showing routes to further increase the readout speed.

Triple-Resonant Brillouin Light Scattering in Magneto-Optical Cavities.

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

Optical spin-transfer-torque-driven domain-wall motion in a ferromagnetic semiconductor.

We demonstrate optical manipulation of the position of a domain wall in a dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified. First, photocarrier spin exerts a spin-transfer torque on the magnetization via the exchange interaction. The direction of the domain-wall motion can be controlled using the helicity of the laser. Second, the domain wall is attracted to the hot spot generated by the focused laser. Unlike magnetic-field-driven domain-wall depinning, these mechanisms directly drive domain-wall motion, providing an optical tweezerlike ability to position and locally probe domain walls.

Inverse conoscopy: a method to measure polarization using patterns generated by a single birefringent crystal.

A method to measure the full polarization vector of a laser beam is proposed and demonstrated. Light is focused onto a birefringent crystal cut such that the slow axis is aligned with the optical axis. The polarization vector of each ray experiences a rotation about the radial axis with a retardation phase dependent on the angle of incidence. Illumination over a wide range of angles applies a range of polarization transforms in parallel that generates a distinct pattern detected by a camera. The input polarization is then inferred from the pattern. The setup uses a single birefringent crystal and involves no moving parts.