Quantum state swap for two trapped Rydberg atoms

The quantum swap gate is one of the most useful gates for quantum computation. Two-qubit entanglement and a controlled-NOT quantum gate in a neutral Rydberg atom system have been achieved in recent experiments. It is therefore very interesting to propose a scheme here for swapping a quantum state between two trapped neutral atoms via the Rydberg blockade mechanism. The atoms interact with a sequence of laser pulses without individual addressing. The errors of the swap gate due to imprecision of pulse length, finite Rydberg interaction, and atomic spontaneous emission are discussed.     

Quantum wires and quantum dots for neutral atoms

By placing changeable nanofabricated structures (wires, dots, etc.) on an atom mirror one can design guiding and trapping potentials for atoms. These potentials are similar to the electrostatic potentials which trap and guide electrons in semiconductor quantum devices like quantum wires and quantum dots. This technique will allow the fabrication of nanoscale atom optical devices. Received: 28 October 1997 / Revised: 17 February 1998 / Accepted: 17 July 1998     

用于成像超冷费米原子气的量子显微镜

为捕获于光阱中的冷原子拍照,需要配合使用一个快速“闪光”,将它们照亮。而不幸的是,闪光会使冷原子热起来,并将它们从光阱逐出。两个新实验绕过了这个问题,通过使用一组激光光束,在冷却原子的同时,成功地拍摄到一个个冷原子的空间占位。这类量子气显微镜用于成像费米冷原子,尚属首次。新实验为使用冷原子模拟强关联系统中的电子提供了机会,例如模拟高温超导体和超巨磁电阻材料。在过去的几年里,研究人员已经对光学晶格中的玻色原子实现了量子气显微镜成像。使用光频饴(光学粘胶)和其他技术, 在成像过程中保持原子气冷却。与玻色原子相比,费米原子不容易“上像”。这主要是因为,作为费米原子,如锂-6和钾-40,它们更难被冷却。但现在,两个研究组已经成功地摄取了冷费米原子的图像：Zwierlein和他在麻省理工学院的同事展示了他们针对钾原子气的成像技术;而哈佛大学的Greiner等则是完成了对锂原子的成像。     

Quantum computing with alkaline-Earth-metal atoms

We present a complete scheme for quantum information processing using the unique features of alkaline-earth-metal atoms. We show how two completely independent lattices can be formed for the 1S0 and 3P0 states, with one used as a storage lattice for qubits encoded on the nuclear spin, and the other as a transport lattice to move qubits and perform gate operations. We discuss how the 3P2 level can be used for addressing of individual qubits, and how collisional losses from metastable states can be used to perform gates via a lossy blockade mechanism.     

Quantum memory with optically trapped atoms

We report the experimental demonstration of quantum memory for collective atomic states in a far-detuned optical dipole trap. Generation of the collective atomic state is heralded by the detection of a Raman scattered photon and accompanied by storage in the ensemble of atoms. The optical dipole trap provides confinement for the atoms during the quantum storage while retaining the atomic coherence. We probe the quantum storage by cross correlation of the photon pair arising from the Raman scattering and the retrieval of the atomic state stored in the memory. Nonclassical correlations are observed for storage times up to 60 mus.     

Quantum beats from dressed three-level atoms

By extending a previously developed unitary transformation technique to dress three-level atoms by a strong driving radiation field, we show that quantum beats can be induced by the presence of the driving field also when the decay channels lead from a singlet to a doublet of lower energy. A qualitative explanation of this effect is presented, which is based on the quantum theory of measurement.     

Quantum Zeno dynamics in atoms and cavities

Quantum Zeno Dynamics restricts the evolution of a system in a tailorable subspace of the Hilbert space by repeated measurements of a proper observable. This restricted dynamics can be counterintuitive and lead to the generation of interesting nonclassical states. We describe an experiment implementing the Zeno dynamics in an atomic Rydberg level manifold, and we propose an implementation in the cavity quantum electrodynamics context. Both systems open promising perspectives for quantum-enabled metrology and decoherence studies.     

Quantum information processing with atoms and cavities

Cavity quantum electrodynamics (CQED) experiments realize the simplest matter–field system: a single atom coupled to a single field mode containing only a few photons. On the one hand, these experiments can be used to test fundamental features of the quantum world. On the other hand, they implement elementary quantum logic components: qubits and quantum gates. We present here a review of the CQED experiments performed at Ecole Normale Supérieure with circular Rydberg atoms and superconducting millimeter-wave cavities.     

Quantum correlations among superradiant Bose-Einstein condensate atoms

Quantum correlations among atoms in superradiant Bose-Einstein condensates are discussed. It is shown that atoms in the superradiant atomic condensate can exhibit continuous variable quantum entanglement analogous to Einstein-Podolsky-Rosen (EPR)-type quantum correlations. Comparison to quantum entanglement in the Dicke model in thermal equilibrium is provided.     

宏观人工原子相关的量子相干操纵

文章着重介绍作者及其合作者于2005年8月份发表在Physical Review Letters的2篇文章及其相关的系列研究工作．其中包括：（1）利用超导电荷量子比特的“Bang—Bang”控制，去冷却与之相耦合的纳米机械谐振器件，使之接近基态，以展示其丰富的量子效应；（2）具有△型能级结构超导人工原子的物理实现及其绝热量子操纵的奇异特性．为了深入了解这些工作的物理和潜在的应用背景，文章同时也介绍了超导量子比特物理实现及其相关的“全固态系统腔量子电动力学”研究的新进展，强调了基于超导人工原子的强耦合量子光学结构形成的物理机制．     

宏观人工原子相关的量子相干操纵

文章着重介绍作者及其合作者于2005年8月份发表在Physical Review Letters的2篇文章［ 1,2］及其相关的系列研究工作［ 3—5］.其中包括：（1）利用超导电荷量子比特的“Bang-Bang”控制,去冷却与之相耦合的纳米机械谐振器件,使之接近基态,以展示其丰富的量子效应;（2）具有Δ型能级结构超导人工原子的物理实现及其绝热量子操纵的奇异特性.为了深入了解这些工作的物理和潜在的应用背景,文章同时也介绍了超导量子比特物理实现及其相关的 “全固态系统腔量子电动力学”研究的新进展,强调了基于超导人工原子的强耦合量子光学结构形成的物理机制.     

Quantum discord between two moving two-level atoms

Considering a double JC model, this paper investigates the quantum discord dynamics of two isolated moving two-level atoms each interacting with a single-mode thermal cavity field, and studies the effect of the atomic motion and the field-mode structure on quantumdiscord. The results show that, on the one hand the quantum discord evolves periodically with time and the periods are affected by the atomic motion and the field-mode structure; on the other hand, the quantum discord still can capture the quantum correlation between the two atoms when the entanglement is zero. It is interesting to note that the quantum discord can be effectively preserved by controlling the field-mode structure parameter     

Quantum tunneling for separation of atoms and molecules from a mixture

We suggest a technique to separate specific types of isotopes, atoms, and molecules from a mixture. The mechanism is based on the tunneling phenomenon of slowly moving molecules released from a magneto-optical trap. We argue that the scheme suggested can be realized in the laboratory.     

Quantum tunneling of ultracold atoms in optical traps

We review our theoretical advances in quantum tunneling of BoseEinstein condensates in optical traps and in microcavities. By employing a real physical system, the frequencies of the pseudo Goldstone modes in different phases between two optical traps are studied respectivdy, which are tile crucial feature of the non-Abelian Joseptmon effect. When the optical lattices are under gravity, we investigate the quantum tummling in the ＂Wannier-Stark localization＂ regime and ＂Lan（lau Zener tunneling＂ regime. We finally get the total decay rate and the rate is valid over the entire range of temperatures. At high temperatures, we show how the decay rate reduces to the appropriate results for the classical thermal activation. At hltermediate temperatures, the results of tile total decay rate are consistent with the thermally assisted tunneling. At low temperatures, we obtain the pure quantmn tunneling ultimately. And we study the alternating-current and direct-current （ac and de） photonic 3osephson effects in two weakly linked microcavities containing ultracold two-level atones, which allows for direct observation of the effects. This enables new investigations of the effect of maw-body physics in strongly coupled atom-cavity systems and provides a strategy for constructing novel interference devices of coherent photons. In addition, we propose the experimental protocols to observe these quantmn tunneling of Bose- Einstein condensates.     

Quantum control of electron-phonon scatterings in artificial atoms

The phonon-induced dephasing dynamics in optically excited semiconductor quantum dots is studied within the frameworks of the independent boson model and optimal control. We show that appropriate tailoring of laser pulses allow complete control of the optical excitation despite the phonon dephasing, a finding in marked contrast to other environment couplings.     

Quantum simulation of disordered systems with cold atoms

This paper reviews the physics of quantum disorder in relation with a series of experiments using laser-cooled atoms exposed to “kicks” of a standing wave, realizing a paradigmatic model of quantum chaos, the kicked rotor. This dynamical system can be mapped onto a tight-binding Hamiltonian with pseudo-disorder, formally equivalent to the Anderson model of quantum disorder, with quantum chaos playing the role of disorder. This provides a very good quantum simulator for the Anderson physics.     

Quantum chaos of atoms in a resonant cavity

A system of atoms interacting with a radiation field in a resonant cavity is studied under conditions when the dynamics in the classical limit is stochastic. This situation is called quantum chaos. Equations of motion are obtained for the quantum-mechanical expectation values which take into account the quantum correlation functions. It is shown that in a situation corresponding to quantum chaos, the quantum corrections grow exponentially, making the evolution of the system essentially quantal after a certain time tau( variant Planck's over 2pi ) has elapsed. Analytical and numerical analysis show that in this regime the time tau( variant Planck's over 2pi ) obeys the logarithmic law tau( variant Planck's over 2pi ) approximately ln N (N is the number of atoms), and not the law tau( variant Planck's over 2pi ) approximately N(alpha) (alpha is a certain constant of order unity), as would be the case in the absence of chaos.