Rongguo Yang

Bright two-color tripartite entanglement with second harmonic generation

The bright two-color tripartite entanglement is investigated in the process of type II second harmonic generation (SHG) operating above threshold. The two pump fields and the second harmonic field are proved to be entangled, and the dependence of the entanglement degree on pump parametersigma and normalized frequency Omega is also analyzed.

Scheme for efficient extraction of low-frequency signal beyond the quantum limit by frequency-shift detection

Low-frequency (Hz~kHz) squeezing is very important in many schemes of quantum precision measurement. But it is more difficult than that at megahertz-frequency because of the introduction of laser low-frequency technical noise. In this paper, we propose a scheme to obtain a low-frequency signal beyond the quantum limit from the frequency comb in a non-degenerate frequency and degenerate polarization optical parametric amplifier (NOPA) operating below threshold with type I phase matching by frequency-shift detection. Low-frequency squeezing immune to laser technical noise is obtained by a detection system with a local beam of two-frequency intense laser. Furthermore, the low-frequency squeezing can be used for phase measurement in Mach-Zehnder interferometer, and the signal-to-noise ratio (SNR) can be enhanced greatly.

Generating multiplexed entanglement frequency comb in a nondegenerate optical parametric amplifier

In this paper, we propose a scheme to produce a multiplexed entanglement frequency comb in a type II phase-matching nondegenerate optical parametric amplifier (NOPA) operating below threshold. The entanglement of the signal and idler frequency combs in the wide frequency range, which is limited by the phase-matching bandwidth of the NOPA, is investigated by the inseparability criterion. Furthermore, N Einstein–Podolsky–Rosen pairs can be created from the two combs without any reduction in the correlations by using frequency-dependent beam splitters.

Preparation and measurement of tunable high-power sub-Poissonian light using twin beams

Widely frequency tunable bright sub-Poissonian field preparation has been experimentally achieved with quantum-correlated twin beams in the continuously variable regime. The noise of the sub-Poissonian field is reduced to more than 2 dB below the shot-noise level throughout the entire wavelength-tunable range of 7.4 nm. A maximum noise reduction of 45% (2.6 dB) is observed. The statistical distribution of a sub-Poissonian field is also obtained.

Generation of continuous-variable spatial cluster entangled states in optical mode comb

Cluster entangled states are often used as the fundamental resources for one-way quantum computation. In this paper, we put forward a scheme of generating the spatial cluster entangled states of Laguerre–Gaussian modes in a large-Fresnel-number degenerate optical parametric oscillator operating below threshold with type I phase matching, which is pumped by two spatial Laguerre–Gaussian modes with the same frequency. The nonlinear parametric process of each pump mode satisfies momentum, energy, and orbit angular momentum conservation. Eleven-partite spatial cluster entangled states of Laguerre–Gaussian modes can be produced in the optical mode comb under feasible experimental condition, which can be demonstrated by using the entanglement criterion proposed by van Loock and Furusawa.

Large-scale continuous-variable dual-rail cluster entangled state based on spatial mode comb

In recent continuous-variable (CV) multipartite entanglement researches, the number of fully inseparable light modes has been increased dramatically by the introduction of a multiplexing scheme in either the time domain or the frequency domain. In this paper, we propose a scheme that a large-scale (≥ 20) CV dual-rail cluster entangled state is established based on a spatial mode comb in a self-imaging optical parametric oscillator, which is pumped by two spatial Laguerre-Gaussian modes with different polarization and identical frequency. A sufficient condition of full inseparability for a CV dual-rail cluster entangled state is used to evaluate the degree of quantum entanglement. It is shown that entanglement exists over a wide range of analyzing frequency and pump parameter. We have found a new scheme that uses the optical parametric cavity to generate a large-scale entanglement based on optical spatial mode comb. The presented system will be hopefully as a practical entangled source for quantum information.

Generation of squeezed TEM01 modes with periodically poled KTiOPO4 crystal

Spatial quantum optics and quantum information based on the high order transverse mode are of importance for the super-resolution measurement beyond the quantum noise level. We demonstrated experimentally the transverse plane TEM01 Hermite—Gauss quantum squeezing. The squeezed TEM01 mode is generated in a degenerate optical parametric amplifier with the nonlinear crystal of periodically poled KTiOPO4. The level of 2.2-dB squeezing is measured using a spatial balance homodyne detection system.

Transfer of intensity quantum correlation with twin beams

We demonstrate experimentally a protocol of transferring nonclassical quantum properties using two pairs of quantum-correlated twin beams in the continuous variable regime. The intensity quantum correlation from one twin beam is transferred to two initially independent idler beams with the help of a displacement transformation. It makes two originally independent beams exhibit an intensity quantum correlation of 0.8 dB below shot-noise level.

Continuous variables quantum correlation transferring with classical independent intensity beams

We report the first realization of quantum correlation transferring. The initial two correlated twin beams are generated from two separated OPO and laser. The transferred intensity quantum correlation degree of 1 dB below SNL is measured.