Early Posters
Here shows the selected posters of the elder years.
2021
Quantum Frequency Conversion Based on Resonant Four-Wave Mixing
ABSTRACT
Quantum frequency conversion (QFC), a critical technology in photonic quantum information science, requires that the quantum characteristics of the frequency-converted photon must be the same as the input photon except for the color. In nonlinear optics, the wave mixing effect far away from the resonance condition is often used to realize QFC because it can prevent the vacuum field reservoir from destroying the quantum state of the converted photon effectively. However, the strong pump light used in nonlinear optics often generates additional noise photons through spontaneous Raman or parametric conversion processes. Herein, we theoretically study another efficient QFC scheme based on a resonant four-wave mixing system. Due to the effect of electromagnetically induced transparency (EIT), this resonant QFC scheme can greatly suppress vacuum field noise at low light levels; consequently, the converted photons can inherit the quantum state of the input photon with high fidelity. Our research demonstrates that if the conversion efficiency (CE) of the EIT-based QFC is close to 100%, the wave function and quadrature variance of the converted photons are almost the same as the input probe photons. Using this resonant QFC scheme, we observe a wavelength conversion from 780 to 795 nm with a 91.2(6)% CE in a cold 87Rb atomic cloud with an optical depth of 130. The current work shows that our proposed and demonstrated resonant four-wave mixing system is a feasible and promising scheme to realize low-loss, high-fidelity QFC.
2018
High-efficiency backward four-wave mixing by quantum interference
ABSTRACT
Long-distance quantum optical communications usually require efficient wave-mixing processes to convert the wavelengths of single photons. Many quantum applications based on electromagnetically induced transparency (EIT) have been proposed and demonstrated at the photon level, such as quantum memories, all-optical transistors, and cross-phase modulations. However, EIT-based four-wave mixing (FWM) in a resonant double-Λ configuration has a maximum conversion efficiency (CE) of 25% because of absorptive loss due to spontaneous emission. Here, we demonstrate that spontaneous emission can be considerably suppressed by arranging the applied laser beams in a backward configuration. With the backward double-Λ FWM scheme, we observe a CE of 76% in cold rubidium atoms with an optical depth (OD) of 52. Furthermore, we present a theoretical model that includes the phase-mismatch effect in the backward double-Λ FWM system. According to the theoretical model, the present scheme can achieve 96% CE using a medium with a large OD of 200 under ideal conditions. This backward FWM scheme can achieve a near-unity CE, thus providing an easy method of implementing an efficient quantum wavelength converter for narrow-band single photons in all-optical quantum information processing.
2017
Large Cross-Phase Modulations at the Few-Photon Level
ABSTRACT
We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-Λ system. The property of the double-Λ medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing laser beams. With this scheme, we observe a π-level phase shift with two pulses, both consisting of eight photons in cold rubidium atoms. Such a novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing.
2017
Beyond the Conversion Limit in Resonant Four-Wave Mixing Process
ABSTRACT
Long-range quantum optical communication needs a nonlinear process that changes the wavelength of the quantum optical states with high conversion efficiency (CE). However, CE in resonant N-type four-wave mixing (FWM) processes saturates at 25% due to the vacuum field fluctuations. An improved scheme, using spatially varied intensity of two laser fields, for exceeding the conversion limit (25%) has been theoretically proposed. Here, we report the first observation of wavelength conversion with 43% CE by using such scheme at optical depth (OD) of 18 in cold rubidium atoms. According to the theoretical model, CE in the proposed scheme can further increase to 96% at OD of 240, which reaches the same CE compared to previous non-resonant FWM system but only using half of OD. This novel scheme can reach almost unity CE of FWM for a sufficiently large OD, thus providing us to implement a high-fidelity quantum wavelength converter for the practical applications in quantum information science.
2013
Toward Generation of Polarization-Entangled Photons by Four-Wave Mixing
ABSTRACT
We report experimental results toward generation of polarization-entangled photons using N-type four-wave mixing (FWM) in cold {87}^Rb atoms. This FWM scheme is based on a well-known effect of electromagnetically induced transparency (EIT). Using this scheme, we can implement high-brightness polarization-entangled photons with narrow bandwidth. To protect the entangled photons from additional absorption, we optically pumped the atoms into a single Zeeman state [1]. Next, we are going to measure the wave function of the generated entangled photons using quantum-state tomography. In the future, the polarization-entangled photons will be applied in the study of EIT-based quantum storage of superposition states. Such a narrow-bandwidth source of entangled photons is suitable for studying nonlinear optical quantum computation and quantum communication.
2012
THEORETICAL STUDY OF PHASE-DEPENDENT DOUBLE-LAMBDA
ELECTROMAGNETICALLY INDUCED TRANSPARENCY
ABSTRACT
We propose a novel all-optical phase modulation based on a phase-dependent double-Lambda electromagnetically-induced-transparency system. According to our theoretical analysis,
the phase modulation of the double-Lambda system can not only overcome the limitation of the N-type system , but also have the potential to achieve a single-photon p phase gate.
2011
Electromagnetically Induced Transparency Based Cross-Phase Modulation at Attojoule Levels
ABSTRACT
The processing of information based on light often requires strong photon-photon interactions. A promising approach to creating strong photon-photon interactions is the use of electromagnetically induced transparency (EIT). Recently, all-optical switching based on EIT has been realized in an atom-filled hollowfiber with light pulses containing a few hundred photons. However, a more important issue is the all-optical phase control, the so-called cross-phase-modulation (XPM), that can be used to implement quantum phase gates and entangled states. Here we report an experimental demonstration of EIT-based XPM at few-hundred-photon levels. A phase shift of 5 mrad of a probe pulse modulated by a signal pulse with an energy of 100 attojoules, equivalent to about 400 photons, was observed in cold Rubidium atoms. The experimental data show the single-photon-level XPM phase shift is about 1.3×10^-5 rad, which is in good agreement with the theoretical prediction. This work offers exciting prospects to the realization of EIT-based XPM scheme at the single-photon level and benefits experimental development in few-photon applications of EIT-based techniques for quantum optics and quantum information science.
2010
Ultralow-Light-Level Phase Measurement of Slow Light Pulses via Beat-Note Interferometer
ABSTRACT
The phase is one of important and manageable information carried by photons which can be used as qubits in quantum communication and computation, thus the ability to control the optical phase at the single-photon level will be a benefit to quantum information science. In recent decades an unique phenomenon of electromagnetically induced transparency (EIT) with the property of extremely high dispersion has been extensively studied and applied in many interesting subjects. Several studies based on EIT have proposed to efficiently enhance photon-photon interaction even at the single-photon level, such as photon switching and cross-phase modulation. Here we report on an experimental demonstration of applying the beat-note interferometer to simultaneously measure the phase and amplitude variations of light pulses after propagating through an EIT medium at the single-photon levels. Furthermore, we observe that the measured phase noise approaches the shot-noise level arising from the fluctuations of detected photons.