Jiangrui Gao

Experimental Demonstration of Unconditional Entanglement Swapping for Continuous Variables

The unconditional entanglement swapping for continuous variables is experimentally demonstrated. Two initial entangled states are produced from two nondegenerate optical parametric amplifiers operating at de-amplification. Through implementing the direct measurement of the Bell-state between two optical beams from each amplifier the remaining two optical beams, which have never directly interacted with each other, are entangled. The quantum correlation degrees of 1.23 and 1.12 dB below the shot noise limit for the amplitude and phase quadratures resulting from the entanglement swapping are measured straightly.

Optimization and transfer of vacuum squeezing from an optical parametric oscillator

We report the observation of more than 7 dB of vacuum squeezing from a below-threshold optical parametric oscillator (OPO). We discuss design criteria and experimental considerations for its optimization and demonstrate that the vacuum squeezing can be electro-optically transferred to a bright beam using a feed-forward loop. This is compared with the bright intensity squeezed beam generated by running the OPO as a de-amplifier.

Generation and application of twin beams from an optical parametric oscillator including an alpha-cut KTP crystal.

Measurement slight amounts of absorption of light with accuracy beyond the standard quantum limit has been experimentally demonstrated. The quantum-correlated twin beams used in the measurement were generated from a nondegenerate optical parametric oscillator including an alpha-cut KTiOPO(4) crystal pumped by an intracavity frequency-doubled Nd:YAG laser. The noise in the intensity difference between the twin beams was reduced by 88% below the standard quantum limit (SQL). The signal-to-noise ratio was improved by 7 dB with respect to the SQL of the total light employed in the experiment and by 4 dB with respect to that of the signal light.

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.

Design of Compact Frequency-Tuned Microstrip Balun

In this letter, a compact frequency-tuned microstrip balun with a ring structure is proposed. By tuning the capacitance of varactor, the operating frequency of the balun can be tuned continuously. Also, by arranging the two loops on two layers, the difficulty in process caused by narrow gap can be avoided. Meanwhile, by introducing the lumped capacitors, the dimension of the balun is reduced greatly. The measured results indicate that the balun can operate at 620-1020 MHz when the voltage of varactor changes from 4 to 16 V. The phase difference of the two balanced ports is 180° ± 7°, and the amplitude difference is less than 0.8 dB. The realized balun has a dimension of 19.6 × 16.8 mm², equal to λ₀/25 × λ₀/29 (λ₀, the wavelength in vacuum at 620 MHz).

Low-frequency phase measurement with high-frequency squeezing.

Squeezed-state enhanced audio-frequency signal measurement is crucial for some special applications, such as gravitational wave detection. But generation of squeezed state of light at such frequency is more difficult than that at megahertz-frequency. In this paper we propose an experimental scheme to measure low-frequency phase signal with high-frequency squeezing. To utilize the high-frequency sidebands of the squeezed light, a two-frequency intense laser is applied in the interferometry instead of a single-frequency laser as usual. This technique is in the reach of modern quantum optics technology.

Bright quadripartite continuous variable entanglement from coupled intracavity nonlinearities

The continuous variable quadripartite entanglement properties of the output fields by the coupled intracavity parametric downconversions processes are analyzed theoretically. In the above-threshold region, it shows that the four output lights are multicolored entangled beams in separable locations with four-mode amplitude quadratures correlation and relative phase quadratures correlation.

Small-displacement measurements using high-order Hermite-Gauss modes

We present a scheme for small-displacement measurements using high-order Hermite-Gauss modes and balanced homodyne detection. We demonstrate its use with experimental results of displacement measurements using fundamental transverse mode TEM00 and first order transverse mode TEM10 as signal modes. The results show a factor of 1.41 improvement in measurement precision with the TEM10 mode compared with that with the TEM00 mode. This scheme has potential applications in precision metrology, atomic force microscopy, and optical imaging.

Tunable continuous-wave doubly resonant optical parametric oscillator by use of a semimonolithic KTP crystal

A temperature-tuned continuous-wave doubly resonant optical parametric oscillator (OPO) consisting of a semimonolithic KTP crystal and a concave mirror has been designed and built. Under single-axial-mode-pair operation, we obtained a combined output power of the signal and idler light fields up to 365 mW at a pump power of 680 mW. The output wavelength of the OPO can be temperature tuned by as much as 9 nm. We achieved 2.8-GHz continuous frequency tuning of the OPO by tuning the pump laser frequency.

Fidelity with quadrature component variances for continuous-variable quantum teleportation

The efficiency of continuous-variable quantum teleportation is typically quantified by fidelity especially in experiment. From the original definition of fidelity in two pure states, we give an expansion of fidelity which is related to the variances of output and input states. With a coherent or a squeezed input state, it is convenient to quantify the quantum teleportation experiment, since the variances of quadrature components of the input and output states are measurable. Furthermore, the fidelity was discussed when the quantum channel lies in the phase- and amplitude-noisy environment, which is unavoidable in experiment, and this showed that the effect of phase noise on teleportation is more sensitive than that of the amplitude-noisy environment. The classical fidelity limit of squeezed state quantum teleportation is also obtained when the entanglement resources do not exist.