Trapping and Cooling of Single Atoms in an Optical Microcavity by a Magic-Wavelength Dipole Trap

We present trapping and cooling of single cesium atoms inside a microcavity by means of an intracavity far-off- resonance trap （FORT）. By the ＇magic＇ wavelength FORT, we achieve state-insensitive single-atom trapping and cooling in a microeavity. The cavity transmission of the probe beam strongly coupled to single atoms enables us to continuously observe the intracavity atom trapping. The average atomic localization time inside the bright FORT is about 7ms by introducing cavity cooling with appropriate detuning. This experiment presents great potential in coherent state manipulation for strongly coupled atom photon systems in the context of cavity quantum electrodynamics.

Single-photon scattering by two separated atoms in a supercavity

We study the single-photon scattering along a one-dimensional cavity array with two distant two-level atoms in a supercavity,which aims to simulate a recent x-ray experiment [Nature 482,199（2012）].Without introducing dissipation,we find that when one atom is exactly located at a node of a mode of the supercavity and the other is at the antinode of that mode,no splitting of the reflectivity peak can appear.Nevertheless,the atom at the node significantly changes the positions of the reflectivity valleys.On the other hand,when the atom is shifted a little from the exact node,then the splitting can appear.We also explain these results with an analysis based on the general formal scattering theory.Our result implies the importance of non-resonant modes of the supercavity in our problem.

Faithfully probabilistic teleportation of an unknown atomic state and cavity field state with a single measurement

This paper shows that, based on the single-photon JC model depicting the resonant interaction of a two-level atom with a single cavity mode, an unknown atomic state and cavity photon superposition state can be faithfully telcported with only a single measurement. The scheme is probabilistie, its success lies on the event that the sender atom （or the medi-atom, for teleportation of cavity field state） is detected in the higher state. The scheme is in contrast to the previous ones of using a maximally two-particle entangled state as quantum channel.

Superconducting Nanowire Single Photon Detector with Optical Cavity

Increasing the detection efficiency （DE） is a hot issue in the development of the superconducting nanowire single photon detector （SNSPD）. In this work, a cavity-integrated structure coupled to the SNSPD is used to enhance the light absorption of nanowire. Ultra-thin Nb films are successfully prepared by magnetron sputtering, which are used to fabricate Nb/Al SNSPD with the curve of lOOnm and the square area of 4 × 4μm2 by sputtering and the lift-off method. To characterize the optical and electrical performance of the cavity-integrated SNSPD, a reliable cryogenic research system is built up based on a He3 system. To satisfy the need of light coupling, a packaging structure with collimator is conducted. Both DE and the dark count rates increase with lb. It is also found that the DE of SNSPD with cavities can be up to 0.17% at the temperature of 0.7K under the infrared light of 1550nm, which is obviously higher than that of the SNSPD directly fabricated upon silicon without any cavity structure.

Single photon transport properties in coupled cavity arrays nonlocally coupled to a two-level atom in the presence of dissipation

We discuss the effects of dissipation on the behavior of single photon transport in a system of coupled cavity arrays, with the two nearest cavities nonlocally coupled to a two-level atom. The single photon transmission amplitude is solved exactly by employing the quasi-boson picture. We investigate two different situations of local and nonlocal couplings, respectively. Comparing the dissipative case with the nondissipative one reveals that the dissipation of the system increases the middle dip and lowers the peak of the single photon transmission amplitudes, broadening the line width of the transport spectrum. It should be noted that the influence of the cavity dissipation to the single photon transport spectrum is asymmet- ric. By comparing the nonlocal coupling with the local one, one can find that the enhancement of the middle dip of single photon transmission amplitudes is mostly caused by the atom dissipation and that the reduced peak is mainly caused by the cavity dissipation, no matter whether it is a nonlocal or local coupling case. Whereas in the nonlocal coupling case, when the coupling strength gets stronger, the cavity dissipation has a greater effect on the single photon transport spectrum and the atom dissipation affection becomes weak, so it can be ignored.

Micropillar Cavity Design for 1.55-μm Quantum-Dot Single-Photon Sources

The 1.55-μm quantum-dot (QD) micropillar cavities are strongly required as single photon sources (SPSs) for silica-fiber-based quantum information processing. Theoretical analysis shows that the adiabatic distributed Bragg reflector (DBR) structure may greatly improve the quality of a micropillar cavity. An InGaAsP/InP micropillar cavity is originally difficult, but it becomes more likely usable with inserted tapered (thickness decreased towards the center) distributed DBRs. Simulation turns out that, incorporating adiabatically tapered DBRs, a Si/SiO2- InP hybrid micropillar cavity, which enables weakly coupling InAs/InP quantum dots (QDs), can even well satisfy strong coupling at a smaller diameter. Certainly, not only the tapered structure, other adiabatic designs, e.g., both DBR layers getting thicker and one thicker one thinner, also improve the quality, reduce the diameter, and degrade the fabrication difficulty of Si/SiO2-InP hybrid micropillar cavities. Furthermore, the problem of the thin epitaxial semiconductor layer can also be greatly resolved by inserting adiabatic InGaAsP/InP DBRs. With tapered DBRs, the InGaAsP/InP-air-aperture micro-pillar cavity serves as an efficient, coherent, and monolithically producible 1.55-μm single-photon source (SPS). The adiabatic design is thus an effective way to obtain prospective candidates for 1.55-μm QD SPSs.

A solvable operator motion equation of an excited-atom coupled leaky cavity in single-photon generation

A model for an excited-atom coupled leaky cavity in single-photon generation is proposed based on universal modes. Solvable motion equations of the atomic operators are obtained under the single-photon condition by adopting the Lorentzian line type of the universal modes.

Resonant cavity-enhanced quantum dot field-effect transistor as a single-photon detector

A resonant cavity-enhanced （RCE） quantum dot （QD） field-effect transistor （RCEQDFET） is designed for single- photon detection in this paper. Adding distributed Bragg reflection （DBR） mirrors to the single-photon detector （SPD）, we improve the light absorption efficiency of the SPD. The effects of the reflectivity of the mirrors, the thickness and light absorption coefficient of the absorbing layer on the detector＇s light absorption efficiency are investigated, and the resonant cavity is determined by using the air/semiconductor interface as the mirror on the top. Through analyzing the relationship between the refractive index of AlxGal_xAs and A1 component, we choose A1As/Alo.15Gao.85As as the material of the mirror on the bottom. The pairs of A1As/Alo.15Gao.85As film are further determined to be 21 by calculating the reflectivity of the mirror. The detector is fabricated from semiconductor heterostructures grown by molecular beam epitaxy. The reflection spectrum, photoluminescence （PL） spectrum, photocurrent response, and channel current of the detector are tested and the results show that the RCEQDFET-SPD designed in this paper has better performances in photonic response and wavelength selection.

Enhanced single photon emission in silicon carbide with Bull's eye cavities

The authors demonstrate a Bull's eye cavity design that is composed of circular Bragg gratings and micropillar optical cavity in 4H silicon carbide(4H-SiC) for single photon emission. Numerical calculations are used to investigate and optimize the emission rate and directionality of emission. Thanks to the optical mode resonances and Bragg reflections,the radiative decay rates of a dipole embedded in the cavity center is enhanced by 12.8 times as compared to that from a bulk 4H-SiC. In particular, a convergent angular distribution of the emission in far field is simultaneously achieved, which remarkably boost the collection efficiency. The findings of this work provide an alternative architecture to manipulate light-matter interactions for achieving high-efficient SiC single photon sources towards applications in quantum information technologies.

Deterministic Generation of Quantum State Transfer Between Spatially Separated Single Molecule Magnets

We propose a new scheme for realizing deterministic quantum state transfer (QST) between two spatiallyseparated single molecule magnets (SMMs) with the framework of cavity quantum electrodynamics (QED).In the presentscheme,two SMMs are trapped in two spatially separated optical cavities coupled by an optical fiber.Through strictlynumerically simulating,we demonstrate that our scheme is robust with respect to the SMMs' spontaneous decay andfiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber.In addition,wealso discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate thegeneration of QST with high fidelity utilizing the current experimental technology.The present investigation providesresearch opportunities for realizing QST between solid-state qubits and may result in a substantial impact on the progressof solid-state-based quantum communications network.

The remote implementation of all possible generalized quantum measurements on a single atomic qubit in a quantum network

To implement generalized quantum measurement （GQM） one has to extend the original Hilbert space. Generally speaking, the additional dimensions of the ancilla space increase as the number of the operators of the GQM n increases. This paper presents a scheme for deterministically implementing all possible n-operator CQMs on a single atomic qubit by using only one 2-dimensional ancillary atomic qubit repeatedly, which remarkably reduces the complexity of the realistic physical system. Here the qubit is encoded in the internal states of an atom trapped in an optical cavity and single-photon pulses are employed to provide the interaction between qubits. It shows that the scheme can be performed remotely, and thus it is suitable for implementing CQM in a quantum network. What is more, the number of the total ancilla dimensions in our scheme achieves the theoretic low bound.

Scheme for implementing an economical phase-covariant quantum cloning machine of distant atomic qubits with single-photon interference

By means of cavity-assisted photon interference, a simple scheme is proposed to implement a symmetric economical phase-covariant quantum cloning machine of two remote qubits, with each in a separate cavity. With our present scheme, a high-fidelity cloning machine is realized. Our scheme may be quite useful in terms of distributed quantum information processing.

非对称单巨原子腔阵列波导QED系统中的单光子散射

研究单巨原子腔阵列波导量子电动力学(quantum electrodynamics,QED)系统在不对称耦合情形下的单光子散射态.在实空间中推导出系统散射振幅的解析解,并据此分析巨原子通过2个耦合点与波导非对称耦合时,耦合的不对称度和耦合点间距等因素对单光子散射谱的影响.发现,如果巨原子2个耦合点非对称度较大,这时无论耦合点间距大小,系统的散射谱均与小原子类似;而如果非对称度较小且耦合点间距较大时,由于巨原子的非偶极效应的影响,散射谱会出现与小原子截然不同的线型.

两原子三维纠缠态的一步制备

基于单模腔囚禁两个里德堡原子系统,提出一步制备两原子三维纠缠态方案。既节省制备时间和资源,又降低实验复杂性。基于主方程的数值模拟结果表明,所制备的三维纠缠态对腔耗散和里德堡态耗散具有强的鲁棒性。

条件量子相位门的腔QED实现

利用单模场和一个Λ-型三能级原子实现二量子比特的条件量子相位门(CQPG),量子信息编码在单模场的FOCK态和及Λ-型三能级原子的2个亚稳态和上。相位门的实现既不需要其它腔模,也不需要其它原子来纠缠2个量子比特,只要求腔模频率与对应的原子能级跃迁共振耦合。因此,这一方案比过去已报道的大多数方案要简单。

Vertical cavity surface emitting laser transverse mode and polarization control by elliptical hole photonic crystal

The polarization of traditional photonic crystal（PC） vertical cavity surface emitting laser（VCSEL） is uncontrollable,resulting in the bit error increasing easily.Elliptical hole photonic crystal can control the transverse mode and polarization of VCSEL efficiently.We analyze the far field divergence angle,and birefringence of elliptical hole PC VCSEL.When the ratio of minor axis to major axis b/a = 0.7,the PC VCSEL can obtain single mode and polarization.According to the simulation results,we fabricate the device successfully.The output power is 1.7 mW,the far field divergence angle is less than 10°,and the side mode suppression ratio is over 30 dB.The output power in the Y direction is 20 times that in the X direction.

Entanglement Purification Through Cavity Input-Output Process

We propose a scheme to purify entanglement of two atoms from not-too-impure entangled states by checking the parity of the two atoms through the cavity input-output process.As the parity check is made by measurement on single-photon polarization,which would not affect the entanglement of the two atoms,our scheme has the successful probability double of that in a previous well-known scheme with linear optical elements [Nature (London)410 (2001) 1067],and is insensitive to the photon loss and the detection inefficiency.Experimental feasibility of our scheme with current technology is discussed.

Detecting a single atom in a cavity using the χ^((2)) nonlinear medium

We propose a protocol for detecting a single atom in a cavity with the help of the χ^((2)) nonlinear medium.When the χ^((2)) nonlinear medium is driven by an external laser field,the cavity mode will be squeezed,and thus one can obtain an exponentially enhanced light-matter coupling.Such a strong coupling between the atom and the cavity field can significantly change the output photon flux,the quantum fluctuations,the quantum statistical property,and the photon number distributions of the cavity field.This provides practical strategies to determine the presence or absence of an atom in a cavity.The proposed protocol exhibits some advantages,such as controllable squeezing strength and exponential increase of atom-cavity coupling strength,which make the experimental phenomenon more obvious.We hope that this protocol can supplement the existing intracavity single-atom detection protocols and provide a promise for quantum sensing in different quantum systems.

用于铯原子里德伯态激发的509nm波长脉冲激光系统

介绍了一种用于里德伯原子激发的纳秒脉冲激光系统.实验利用两个kHz线宽的1018 nm连续激光器作为种子源,通过两个20GHz带宽的光纤调制器产生时间分离的脉冲激光;脉冲激光经掺镱光纤放大器后输出峰值功率约4600 W,单次穿过PPLN(周期极化铌酸锂)晶体倍频获得509 nm脉冲激光,典型脉冲激光峰值功率约173W.该激光系统单路输出脉冲重复频率在300 kHz-100 MHz范围连续可调,脉宽在1-100 ns范围连续可调.该509 nm激光在聚焦条件下可以实现GHz带宽的铯原子里德伯态激发.