Overcoming synthesizer phase noise in quantum sensing

Abstract

Synthesizers are widely used in various quantum information platforms as microwave or radio frequency signal sources. The synthesizer phase noise plays a sensitive role in detecting spin dynamics which is similar to the environment dephasing. When using spins to measure the environmental magnetic field, synthesizer phase noise reduces the accuracy of the measurement because it is difficult to distinguish the effective field caused by the phase noise from the environmental field.

Suppressing the synthesizer phase noise is important in sensing. This work proposes a scheme to suppress the phase noise from synthesizers using two single-spin systems in opposite static magnetic fields. The two spins are exposed to the same environmental magnetic field which is to be sensed, and controlled by the same synthesizer.

Two configurations of the scheme are constructed: one uses two antennas for control and detection and the other uses one antenna. Because the two spins experience the phase noise in opposite ways, the phase noise effect can be either canceled or separated from that of the environmental field. While the scheme is based on the Ramsey fringe sequence, it can be extended to the Hahn echo and the stimulated echo sequences as well. The basic idea of the scheme in principle works for different quantum information platforms where the Zeeman interaction is the dominant Hamiltonian.

Nuclear magnetic resonance(NMR) platform is used to experimentally simulate the sensing process using the one-antenna configuration, where the information of the environment field is encoded in the amplitude of the NMR signal, and thus separated from the synthesizer phase noise. The experiment demonstrated successfully the proposed scheme.