Injection Locking for Spectral Filtering of the Addressing Laser for Optical Qubits in 171Yb+ Ions

We demonstrate the implementation of a diode laser with high frequency stability at averaging times of 0.1 s to 100 s and low high-frequency phase noise (up to 5 MHz) to control the quantum state of optical qubits based on ¹⁷¹Yb⁺ ions. A high-finesse ULE glass optical cavity is used as an external reference to stabilize the laser frequency and as a spectral filter for high-frequency noise. The calculated suppression of laser phase noise by the cavity at a frequency of 1.2 MHz (where the laser noise density before the filtering reaches its maximum) is 49 dB. Injection locking makes it possible to amplify spectrally pure laser light and use it to control the quantum state of qubits. The spectral purity of the slave laser diode emission is studied by measuring the beat signal of the amplified emission relative to the light transmitted through the cavity. It is shown that the phase noise introduced by injection locking does not exceed -70 dBc in a bandwidth of up to 5 MHz, while an output power of up to 30 mW was achieved.