Effect of phase-sensitive manipulations on generation of low frequency two-mode orthogonal squeezed vacuum states

Abstract

Two-mode orthogonal squeezed vacuum states are an important quantum resource for quantum communication, quantum computing, quantum simulation, quantum precision measurement and sensing. It is essential to get stable two-mode orthogonal squeezed vacuum states with low frequency range and compact configurations for practical applications, especially for quantum precision measurement and sensing. Two-mode orthogonal squeezed vacuum states are commonly produced via a subthreshold nondegenerate optical parametric amplifier (NOPA) in continuous variables systems. However, it is a difficult problem that the subthreshold NOPA cavity is phase sensitive manipulated to obtain stable squeezed vacuum states. Previous signal light injecting scheme relies on an injection of a weak light field into the subthreshold NOPA for phase sensitive manipulation. The injected signal light has the same frequency with the generated squeezed vacuum states. Thereby even the weakest injected signal light can introduce large amounts of excess noise at low frequencies and the squeezing degree of two-mode squeezed vacuum states will be decreased or squeezing cannot be achieved. In this paper, a single sideband frequency shifted light injecting scheme is proposed for phase sensitive manipulation of NOPA. The comparison of single sideband frequency shifted light injecting scheme and signal light injecting scheme for realization of phase sensitive manipulation of NOPA was studied. The effects of the two schemes on the generation of the low-frequency two-mode orthogonal squeezed vacuum state light field were experimentally investigated. The experimental results show that the squeezing degree of the two mode orthogonal squeezed vacuum state continuously decreased until it disappeared as the power of injected signal light increasing with the signal light injecting scheme for phase sensitive manipulation. During the process of phase sensitive manipulation of NOPA by using the single sideband frequency shifted light injecting scheme, the squeezing degree of the two mode orthogonal squeezed vacuum state was not changed with the power of the injected frequency shifted light increasing. Stable phase sensitive manipulation was realized by injecting single sideband frequency shifted light into NOPA. NOPA was operated in a phase sensitive amplification state for 30 minutes. Stable low-frequency two mode orthogonal squeezed vacuum states were obtained. 4.1 ±0.1 dB amplitude orthogonal squeezed vacuum states and 4.0 ±0.2 dB phase orthogonal squeezed vacuum states at the frequency of 200 kHz were generated stably with a compact NOPA configuration.