Measurement of the squeezed vacuum state by a bichromatic local oscillator

Abstract

We present the experimental measurement of a squeezed vacuum state by means of a bichromatic local oscillator (BLO). A pair of local oscillators at ±5 MHz around the central frequency ω 0 of the fundamental field with equal power are generated by three acousto-optic modulators and phase-locked, which are used as a BLO. The squeezed vacuum light are detected by a phase-sensitive balanced-homodyne detection with a BLO. The baseband signal around ω 0 combined with a broad squeezed field can be detected with the sensitivity below the shot-noise limit, in which the baseband signal is shifted to the vicinity of 5 MHz (the half of the BLO separation into the vicinity of 5 MHz ((the half of the BLO separation) and sub-shot-noise detection is implemented. Thus this work with the BLO and broadband squeezing can be used to enhance the signal-to-noise ratio (SNR) of an interferometer for lower frequency phase measurement [24,25].The schematic diagram of the detection is shown in Fig. 1. A strong BLO (at ±Ω 0 around the central frequency ω 0 of the fundamental field with equal power) is mixed with the signal light field at a 50/50 beam splitter. The relative phase θ of the local oscillator and the signal field can be controlled by the reflective mirror mounted on a PZT (piezoelectric transducer). The annihilation operators of the bichromatic local oscillator and the signal field can be written aŝ a(t) =â + (t) exp[−i(ω 0 + Ω 0 )t] +â − (t) exp[−i(ω 0 − Ω 0 )t] andb(t) =b 0 (t) exp (−iω 0 t), whereâ +(−) (t) andb 0 (t) are the slow varying operators of the fields. The output 1

Heterodyne detection enhanced by quantum correlation

“…Using amplitude-squeezed local oscillator, the quantum noise of a one-port heterodyne detector may be reduced [11], yet the problem of the 3 dB extra heterodyne noise due to the image band vacuum was not addressed. A phase-sensitive (PS) heterodyne detector with a bichromatic local oscillator has proven to be noiseless [12][13][14][15][16], but its phase sensitivity [14] requires phase control for the input signal that is intractable in the detection scheme of ongoing space-based GW experiments where violent disturbance to the phase of the input signal is inevitable [1][2][3].…”

“…sin θ l sin(Ωt − ∆θ) , (13) where ∆θ = ∆k • r − θ s , θ s is the phase of the signal mode, ∆k ≡ k s − k l = k l − k i , and we make use of ω s ≈ ω i since |ω s − ω i | << ω s,i for heterodyne detection. In addition, the detector assumes a sufficient response speed in photoemission, and hence j(t) = eδ(t) where δ(t) is Dirac function with e being the charge on the electron.…”

“…The good news is that, no matter what the input phase θ s is, the amplifier will automatically amplify the cos(Ωt − ∆θ) quadrature component of the detected signal with a gain of G = e r , as shown by Eq. (13). Therefore, the practical difficulty in the phase control for the input signal imposed by spacebased GW experiments does not put any fundamental limit to the implementation of heterodyne detection enhanced by quantum correlation.…”

Intra-Mode Squeezing in the Quantum Optical Frequency Comb

“…The central frequency of the broadband light is ω 0 and the two local oscillator frequencies are ω 0 ± Ω 0 . The difference in photo-currents in our homodyne measurement analyzed at a specific radio frequency Ω is [14] …”

“…The number of modes available using this process is limited only by the bandwidth of the cavity mode, the linewidth of the OPO pump, and the bandwidth of the squeezing/entanglement verification measurement. Previous work in this area established the validity of the technique, but only one frequency separation between the two modes was used [12,13,14]. The method presented in this thesis successfully generates and verifies the presence of many entangled modes within a relatively narrow bandwidth.…”