Ding Liang-en

Experimental observation of constructive quantum interference via hybrid excitation in an Na2-Na system

We report on an experimental observation of constructive quantum interference between two atomic transition pathways 3P1/2-5S (or 4D) and 3P3/2-5S (or 4D) via equal-frequency hybrid excitation and collision-aided radiative excitation in an Na2-Na system. Through the special excitation processes, constructive quantum interference is realized for a Λ-type quantum-beat configuration with a widely-spaced doublet (about 17 cm-1) in the excited sodium atom driven by one laser. The dependences of quantum interference on the argon buffer gas pressure and sample temperature are also examined.

Experimental System for Quantum Cryptography Based on Two Nonorthogonal Photon Polarization States

Quantum cryptography allows the establishing of a highly confidential sequence of random bits between two parties who share no secret information in advance. Its security is guaranteed by the basic laws of quantum mechanics rather than mathematical difficulty. An experimental system based on a novel protocol for quantum cryptography using only two nonorthogonal photon polarization states is implemented. The photon sources are two semiconductor laser diodes operated at 680 nm, their light pulses which are heavily attenuated to far below one photon per pulse are employed to encode the key. Gated single photon detection technique is used to minimize the dark count effect of the photon multiplier tube. Key establishing rate of 40 b/s and error rate of 2.1% are obtained. Compared with other systems, our system has the simplest experimental setup.

Effect of four-wave mixing on electromagnetically induced transparency in ?-type system with a two-photon probe field

Using density matrix equation, we calculate analytically as well as numerically the effect of the four-wave mixing (FWM) field on electromagnetically induced transparency (EIT) in the rubidium 5S1/2-5P3/2-5D5/2 Λ-type system with a two-photon probe field. The calculated results are in good agreement with Fultons experimental results in 1995 Phys. Rev. A 52 2302.

Special line-shapes of two-photon transitions in a Y-type four-level system based on quantum interference

The experimentally observed special lineshape, induced by the interaction between two counter-propagating equal-frequency fields and a Y-type four-level system with two mixed upper levels, has been analysed theoretically. Serious lineshape variations of the two-photon transitions due to quantum interference are discussed and predicted.

Observation of Collimated Atoms by Light Pressure Force in Absorption Cell

Experimental observation of laser cooling and collimation of moving atoms in an absorption cell by light pressure force of an intense standing light wave field is reported. The hyper fine structure of atomic sodium has been observed due to the cooled and collimated atoms. The mechanism of laser cooling and collimation of atoms is discussed.

Phase noise suppression and feedback control of carrier-envelope phase in an Yb-doped fiber frequency comb

In this letter, we study the carrier envelope phase noise induced by the effects of LD-pump jitter, temperature change and mechanical vibration on an Yb-doped fiber frequency comb. Based on a home-made Yb-doped fiber oscillator with 60 MHz repetition rate, after two- stage amplifiers and a self-referenced f-2f measurement system, a beat signal with a signal to noise ratio of 25 dB is obtained. Further the frequency of carrier envelope phase signal is locked through phase-lock-loop electronics, a measured residual frequency jitter of 283 mHz is achieved in 0.5 h accumulation time.

Constructive interference via collision-aided radiative excitation

We have studied theoretically constructive interference via collision-aided radiative excitation in an open four-level system using a density matrix approach. The four-level system consists of a Λ-type three-level quantum-beat configuration driven by one laser field and a fourth level coupled by a vacuum mode. It is shown that through the incoherent process (collision), coherence between widely-separated doublets and subsequent constructive interference can be realized. We analyse the effects of the collision-induced coherent and incoherent decay rates, laser intensity and energy separation of the doublets on the interference. Meanwhile, the constructive interference between the two transition pathways 3P1/2-4D and 3P3/2-4D via equal-frequency hybrid excitation and collision-aided radiative excitation in an Na2-Na system is experimentally observed. A good agreement between the theoretical and experimental results is obtained.

Population trapping in multi-level system via quantum interference

Population trapping via quantum interference in a multi-level system driven by a coherent field is investigated. The influences of the alignment of the transition dipole moments and the energy-level separation of the upper levels are taken into account. Detailed trapping population profiles under the different conditions are given. The research result is helpful for simplifying the theoretical model and selecting rational energy level system.

Discovery of the Induced Superslow Optical Relaxation Processes in I2

We discover superslow optical processes with relaxation time as long as 250 ms in I2. The demonstration is performed by a series of experiments with novel considerations for I2 interacting with phase modulated laser fields, monitored by both coherent and noncoherent detection with digital frequency scale and time scale simultaneously for comparison.

FREQUENCY-MODULATION OPTICAL-OPTICAL TRIPLE-RESONANCE OPTICAL HETERODYNE SPECTROSCOPY

We propose new frequency-modulation optical-optical triple-resonance (FM-OOTR) optical heterodyne spectroscopy, which can eliminate the Doppler-background in the recently developed optical-optical triple-resonance (OOTR) spectroscopy and provide improved resolution and sensitivity. Theoretical considerations and line shape calculations are presented. The potential applications of FM-OOTR technique to laser frequency stabilization with significant advantages can be expected.