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 obtain stable two-mode orthogonal squeezed vacuum states in a low frequency range and compact configurations for practical applications,especially in quantum precision measurement and sensing.Two-mode orthogonal squeezed vacuum states are commonly produced via a subthreshold nondegenerate optical parametric amplifier(NOPA)in a continuous variable system.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 as the generated squeezed vacuum state.Thereby even the weakest injected signal light can introduce large amounts of excessive noise at low frequencies and the squeezing degree of two-mode squeezed vacuum states will be reduced 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 between the single sideband frequency shifted light injecting scheme and the signal light injecting scheme for realization of phase sensitive manipulation of NOPA is conducted.The effects of the two schemes on the generation of the low-frequency two-mode orthogonal squeezed vacuum state light field are investigated experimentally.The experimental results show that in the signal light injecting scheme for phase sensitive manipulation,the squeezing degree of the two-mode orthogonal squeezed vacuum state continuously decreases until it disappears as the power of injected signal light increases.In 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 does not change with the power of the injected frequency shifted light increasing.Stable phase sensitive manipulation is realized by injecting single sideband frequency shifted light into NOPA.The NOPA is operated in a phase sensitive amplification state for 30 min.Stable low-frequency two-mode orthogonal squeezed vacuum states are obtained.The(4.1±0.1)dB amplitude orthogonal squeezed vacuum states and(4.0±0.2)dB phase orthogonal squeezed vacuum states at a frequency of 200 kHz are generated stably,in a compact NOPA configuration.
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