## 3 Experimental Setup and Results  
Experimental setup for the generation and transferring of squeezed state of light is shown in Figure 2. An optical parametric amplifier (OPA) [39], which contained a pair of concave mirrors and a type-0 quasi-phase-matched periodically poled KTiOPO\({}_{4}\) (PPKTP) crystals with dimensions of 1 \(\times\) 2 \(\times\) 12 mm\({}^{3}\), was used to generate the squeezed state of light at wavelength of 1342 nm pumped by a Nd:YVO\({}_{4}\) all-solid-state laser [40]. The diameters of both concave mirrors was 10 mm and the curvature radii were 50 mm. The input mirror was coated with high reflection at 1342 nm and transmission T = 20% at 671 nm, and the output mirror was coated with transmission T = 10% at 1342 nm and high reflection at 671 nm. When the OPA worked under deamplification conditions, i.e., the relative phase between the pump beam and the seeded signal beam is maintained at \(\pi+2k\pi\) (\(k\) is an integer), amplitude squeezed state of light was generated. Because the backscattering noise from fiber can be coupled to OPA and affect its stability, two isolators (ISO) with a total loss of 10% were placed in the path of the output beam of the OPA. The LO beam which came from pump laser was chopped to a sequence of light pulses with repetition frequency of 10 MHz and duty ratio of 30%. Then, the continuous squeezed state of light and the pulsed LO beam were coupled on PBS1. By rotating half wavelength plates (HWP1 and HWP2) in each light path, we can control the paths of the signal beam and the LO beam which are sent to optical fiber for transmission or BHD1 for the measurement of squeezing. When the signal beam and the LO beam were all coupled to the BHD1, the squeezing properties of the output beam from OPA can be easily measured, which was 4.04 \(\pm\) 0.16 dB below corresponding QNL. If two ISOs with the transmission efficiency of 90% was removed, the measured squeezing from the OPA was \(5.08\pm 0.16\) dB below corresponding QNL. On the output port of the fiber, the signal beam and the LO beam were separated by an adjusting polarization controller (PC) [41], HWP3 and PBS2. If the two beams were directly sent to the BHD2 for the measurement of noise, the squeezing may be deposited in the extra noise. In order to measure the part of the signal beam without the influence of GAWBS extra noise, the pulsed LO beam is delayed in a 15 m free space OPD. After the delay processing, when the signal beam coincided with the LO beam again after PBS3, only the pure squeezed state of light was coincident with the LO beam. Obviously, the quantum state measured by BHD2 is indeed squeezing of the generated state from the OPA. In the experiment, the mode matching between the continuous signal beam and the LO  
Figure 1: The schemes for measuring the noise of quantum state with pulsed local oscillator (LO) beam. (**a**) the pulse time is longer than the handling time. (**b**) The pulse time is shorter than the handling time. The red trace is the LO pulse sequence; the blue trace is the measured noise; and the black trace corresponds the electronic noise of detector. beam was optimized through lenses in the light path, firstly. Then, the mode matching between can be maintained when the LO beam was chopped. Thus our proposal had no influence in the fidelity between the input and output signal beam, and can reduce the influence in the loss of extra devices added in the light path of the signal beam. As is well known, the noise coefficient \(\varepsilon\) of GABWS in the fiber was dependent on the analysis frequency [34; 35]. In order to quantitatively evaluate the influence of GAWBS on the quantum state, the exact value of \(\varepsilon\) should be known.