Xiaoxin Ma

All-fiber source of frequency-entangled photon pairs

We present an all-fiber source of frequency-entangled photon pairs by using four-wave mixing in a Sagnac fiber loop. Special care is taken to suppress the impurity of the frequency entanglement by cooling the fiber and by matching the polarization modes of the photon pairs counterpropagating in the fiber loop. Coincidence detection of signal and idler photons, which are created in pair and in different spatial modes of the fiber loop, shows the quantum interference in the form of spatial beating, while the single counts of the individual signal (idler) photons keep constant. When the production rate of photon pairs in each propagation direction of the fiber loop is about 0.065 pairs/pulse, the envelope of the quantum interference reveals a visibility of

Spectral study of photon pairs generated in dispersion shifted fiber with a pulsed pump

(95\ifmmode\pm\else\textpm\fi{}2)%

Quantum efficiency measurement of single-photon detectors using photon pairs generated in optical fibers

, which is close to the calculated theoretical limit 98.7%.

Generation of photon pairs in dispersion shift fibers through spontaneous four wave mixing: Influence of self-phase modulation

Spectral correlation of photon pairs generated in dispersion shifted fiber by a pulsed pump is theoretically analyzed and experimentally investigated. We first calculate the spectral function of photon pairs according to the deduced two-photon state generated by spontaneous four wave mixing under the assumptions close to the real experimental conditions. We then experimentally study the spectral property of the signal and idler photon pairs generated in optical fiber by photon correlation measurements, and the experimental results agree with the calculation. The investigation is useful for developing fiber-based sources of entangled photon pairs and for studying multi-photon quantum interference with multiple photon pairs.

Quantum interference between heralded single photon state and coherent state

Using the correlated signal and idler photon pairs generated in a dispersion-shifted fiber by a pulsed pump, we measure the quantum efficiency of an InGaAs/InP avalanche photodiode-based single-photon detector. Since the collection efficiency of photon pairs is a key parameter to correctly deduce the quantum efficiency, we carefully characterize the collection efficiency by studying the correlation dependence of photon pairs on the spectra of pump, signal, and idler photons. This study allows us to obtain the quantum efficiency of the single-photon detector by using photon pairs with various kinds of bandwidth.

Hong–Ou–Mandel interference between independent sources of heralded ultrafast single photons: influence of chirp

Abstract Correlated signal and idler photon pairs with small detuning in the telecom band can be generated through spontaneous four-wave mixing in dispersion shift fibers. However, photons originated from other nonlinear processes in optical fibers, such as Raman scattering and self-phase modulation, may contaminate the photon pairs. It has been proved that photons produced by Raman scattering are the background noise of photon pairs. Here we show that photons induced by self-phase modulation of pump pulses are another origin of background noise. After studying the dependence of self-phase modulation induced photons in signal and idler bands, we demonstrate that the quantum correlation of photon pairs can be degraded by the self-phase modulation effect. The investigations are useful for characterizing and optimizing an all fiber source of photon pairs.

Charactering fiber-based source of heralded single photons

Balanced homodyne detection has been introduced as a reliable technique of reconstructing the quantum state of a single photon Fock state, which is based on coupling the single photon state and a strong coherent local oscillator in a beam splitter and detecting the field quadrature at the output ports separately. The main challenge associated with a tomographic characterization of the single photon state is mode matching between the single photon state and the local oscillator. Utilizing the heralded single photon generated by the spontaneous parametric process, the multi-mode theoretical model of quantum interference between the single photon state and the coherent state in the fiber beam splitter is established. Moreover, the analytical expressions of the temporal-mode matching coefficient and interference visibility and relationship between the two parameters are shown. In the experimental scheme, the interference visibility under various temporal-mode matching coefficients is demonstrated, which is almost accordant with the theoretical value. Our work explores the principle of temporal-mode matching between the single photon state and the coherent photon state, originated from a local oscillator, and could provide guidance for designing the high-performance balanced homodyne detection system.

Temporal coherence property of individual beam generated from spontaneous four wave mixing: Influence of chromatic dispersion induced chirp

For the quantum interference between two truly independent heralded single photon sources (HSPSs), which are generated from the spontaneous parametric processes pumping with ultrafast laser pulses, the visibility of Hong–Ou–Mandel (HOM) interference will be degraded by the mode mismatch. The mode mismatch influenced by the purity of HSPSs has been extensively investigated. Here we show that the chirp of HSPSs will change the pulse duration of ultrafast single photons and introduce additional mode mismatch. To obtain the optimized visibility, which is ultimately determined by the purity of HSPSs, the chirp of each HSPS, originated from its pulsed pump field and propagation media, should be properly managed. Our theoretical analysis shows the methods for minimizing the chirp-induced mode mismatch depend on the bandwidth and phase matching condition of the HSPSs. Our study is useful for designing the HOM interferometers in quantum information processing.

Absolute calibration of photon‐counting detection efficiency using photon pairs generated in optical fibers

Based on the photon pairs generated from an optical fiber by a pulsed pump, we study the second-order coherence function, heralding efficiency, and temporal indistinguishability of the heralded single photons as functions of source parameters.

Characterization of correlated photons in optical fibers

The temporal coherence property of individual beam from spontaneous four wave mixing in optical fibers is experimentally investigated by introducing different amount of chirp into either the pulsed pump or individual signal (idler) beam.