Dynamics of Quantum Correlation of Two Atoms with Photon Recoil

By taking into account spatial degrees of freedom of the atoms, we study the dynamics of the quantum correlation between the electronic states of two atoms, separately placed in two single-mode ring cavities. We show that the quantum correlation of the atomic electronic states can decay to almost zero in a finite time, and the quantum correlation between the cavities depends on the spatial spread of the atoms.     

Inhibition of Atomic Decay in Strongly Coupled Photonic Crystal Cavities

We discuss the evolution dynamics of a quantum system consisting of two two-level atoms separately embedded within two strongly coupled photonic crystal cavities.Although the quantum system is subjected to dissipation and decoherence from the cavity leakage and the atomic decay,it does allow for eigenstates that are not influenced by one of the two dissipation channels and results in dissipation-inhibition quantum states.These dissipationfree quantum states can help to achieve an extremely long photon and atom storage lifetime and provide a new perspective to realize efficient quantum information storage via reducing the negative influence of the dissipation from the environment.     

Dynamics of entanglement transfer from radiation modes to localized qubits

We address the dynamics of entanglement transfer from two radiation modes to a pair of localized qubits implemented as atoms flying through or trapped in separated cavities. We first generalize previous results to include radiation in entangled mixed states and to describe the effect of cavity mirror transmittance. Then we investigate the transfer process by Monte Carlo Wave Function approach, which allows us to solve the whole system dynamics including cavity mode and atomic decays. We focus on flying modes prepared in coherently correlated states and we find realistic conditions for efficient entanglement transfer out of the weak and strong coupling regimes in the perspective of quantum memories realization.     

Voltage-Controlled Quantum Dynamics and Generation Entanglement between Two Separated Quantum-Dot Molecules Embedded in Photonic Crystal Cavities

Voltage-controlled quantum dynamics of two quantum-dot molecules （QDMs） embedded in two separated photonic crystal cavities are theoretically investigated. We show numerically that generation of entangled states and population transfer between the two QDMs can be realized with the same coupling parameters. The effects of parameters deviation and dissipations on generation entangled states be used for realization of new-type of solid state quantum and populations transfer are also discussed. The results may devices and integrated electro-optical devices,     

多原子-腔系统中的量子信息传递

提出了一个多原子-腔组成的物理系统,并讨论了发生在该系统中量子信息的交换和传递过程,结果发现:由最低两个Fock态｜０〉和｜1〉任意组成的光量子态腔场,当处于基态的原子以特定的速度通过腔时,原子都能带走腔中的量子态并据为己有;反之,由两能级原子的基态｜g〉和激发态｜e〉任意组成的量子态,当原子以特定的速度通过处于真空态的腔时,原子都能把携带的量子态释放于腔中,实现了腔-原子之间的信息交换.利用原子能够捡起、释放量子信息这一特点,进一步讨论了把原子作为运输工具实现腔-腔之间异地量子信息传递的物理过程.     

Constructing Robust Entangled Coherent GHZ and W States via a Cavity QED System

Using a system of three distant cavities, we propose a method for constructing tripartite entangled coherent GHZ and W states which are robust due to the photon losses in the cavities. Each of cavities is doped with a semiconductor quantum dot. By the dynamics, the excitonic modes of quantum dots are enabled to exhibit entangled coherent GHZ and W states. Apart from the exciton losses, the master equation approach shows that when the populations of the field modes in the cavities are negligible the destruction of entanglement due to dissipation arises from photon losses, is effectively suppressed.     

The Transfer and Monogamy of Quantum Correlations for Two Qubits

In this paper the entanglement and the quantum discord (QD) dynamics of two cavities interacting with a common independent reservoir are investigated. Remarkably, it has been proved that the entanglement between two cavities can be transferred to one of the cavities and the reservoir with time evolution. Compared with the dynamics of entanglement, the QD has the similar behavior. It is found that the cavity damping rate can stabilize the entanglement and quantum discord between the cavity and reservoir. We also explore the monogamy of the entanglement and the QD during the interaction of quantum system.     

原子与耦合腔相互作用系统中的量子失协

本文研究由两个全同的二能级原子和耦合腔构成的系统,利用Dakic等提出的几何量子失协的度量方法,采用数值计算方法计算了系统中两原子间和两腔场间量子失协的演化.讨论了原子间初始纠缠度和腔场间耦合系数变化对几何量子失协演化的影响.研究发现:随腔场间耦合系数的增大,量子失协周期性演化的频率增大;随原子间初始纠缠度的增大,两原子间的关联增强,两腔场间的关联减弱.     

A quantum computer in the scheme of an atomic quantum transistor with logical encoding of qubits

A scheme of a multiqubit quantum computer on atomic ensembles using a quantum transistor implementing two qubit gates is proposed. We demonstrate how multiatomic ensembles permit one to work with a large number of qubits that are represented in a logical encoding in which each qubit is recorded on a superposition of single-particle states of two atomic ensembles. The access to qubits is implemented by appropriate phasing of quantum states of each of atomic ensembles. An atomic quantum transistor is proposed for use when executing two qubit operations. The quantum transistor effect appears when an excitation quantum is exchanged between two multiatomic ensembles located in two closely positioned QED cavities connected with each other by a gate atom. The dynamics of quantum transfer between atomic ensembles can be different depending on one of two states of the gate atom. Using the possibilities of control for of state of the gate atom, we show the possibility of quantum control for the state of atomic ensembles and, based on this, implementation of basic single and two qubit gates. Possible implementation schemes for a quantum computer on an atomic quantum transistor and their advantages in practical implementation are discussed.     

Distributed qutrit-qutrit entanglement via quantum Zeno dynamics

A scheme is proposed to generate a three-dimensional entangled state for two atoms trapped in two distant cavities via quantum Zeno dynamics. We study such system in the regime of resonant atom-field interactions, which makes the scheme work very fast. We also investigate the influence of dissipation, due to atomic spontaneous emission and photon leakage, on the qutrit-qutrit entanglement.     

Quantum correlations between two cavity QED systems coupled by a mechanical resonator

Achieving quantum correlations between two distant systems is a desirable feature for quantum networking. In this work, we study a system composed of two quantum emitter-cavity subsystems spatially separated. A mechanical resonator couples to either both quantum emitters or both cavities leading to quantum correlations between both subsystems such as non-local light-matter dressed states and cavity–cavity normal mode splitting. These indirect couplings can be explained by an effective Hamiltonian for large energy detuning between the mechanical resonator and the atoms/cavities. Moreover, it is found that the optimal conditions of the physical parameters maximize the entanglement of phonon-mediated couplings.     

Generation of Three-Dimensional Entangled States for Two Atoms Trapped in Different Cavities

We propose a scheme for generating three-dimensional entangled states for two atoms trapped in two separate cavities. The scheme is based on the detection of photons leaking from the cavities after the atom-cavity interaction. The scheme is useful for the test of quantum nonlocality and quantum information processing.     

Asymptotic Entanglement Sudden Death in Two Atoms with Dipole–Dipole and Ising Interactions Coupled to a Radiation Field at Non-Zero Detuning

We investigate the time evolution and asymptotic behavior of a system of two two-level atoms (qubits) interacting off-resonance with a single mode radiation field. The two atoms are coupled to each other through dipole–dipole as well as Ising interactions. An exact analytic solution for the system dynamics that spans the entire phase space is provided. We focus on initial states that cause the system to evolve to entanglement sudden death (ESD) between the two atoms. We find that combining the Ising and dipole–dipole interactions is very powerful in controlling the entanglement dynamics and ESD compared with either one of them separately. Their effects on eliminating ESD may add up constructively or destructively depending on the type of Ising interaction (Ferromagnetic or anti-Ferromagnetic), the detuning parameter value, and the initial state of the system. The asymptotic behavior of the ESD is found to depend substantially on the initial state of the system, where ESD can be entirely eliminated by tuning the system parameters except in the case of an initial correlated Bell state. Interestingly, the entanglement, atomic population and quantum correlation between the two atoms and the field synchronize and reach asymptotically quasi-steady dynamic states. Each one of them ends up as a continuous irregular oscillation, where the collapse periods vanish, with a limited amplitude and an approximately constant mean value that depend on the initial state and the system parameters choice. This indicates an asymptotic continuous exchange of energy (and strong quantum correlation) between the atoms and the field takes place, accompanied by diminished ESD for these chosen setups of the system. This system can be realized in spin states of quantum dots or Rydberg atoms in optical cavities, and superconducting or hybrid qubits in linear resonators.     

Entangled Fields in Multiple Cavities as a Testing Ground for Quantum Mechanics

Entangled states provide the necessary tools for conceptual tests of quantum mechanics and other alternative theories. These tests include local hidden variables theories, pre- and postselective quantum mechanics, QND measurements, complementarity, and tests of quantum mechanics itself against, e.g., the so-called causal communication constraint. We show how to produce various nonlocal entangled states of multiple cavity fields that are useful for these tests, using cavity QED techniques. First, we discuss the generation of the Bell basis states in two entangled cavities, when there is at most one photon in either of the cavities, and then a straightforward generalization to similar N-cavity states. We then show how to produce a nonlocal entangled state when there is precisely one photon hiding in three cavities. These states can be produced by sending appropriately prepared atoms through the cavities. As applications we briefly review two proposals: one to test quantum mechanics against the causal communication constraint using a two-cavity entangled state and the other to test pre- and postselective quantum mechanics using a three-cavity entangled state. The outcome of the latter experiment can be discussed from the viewpoint of the consistent histories interpretation of quantum mechanics and therefore provides an opportunity to subject quantum cosmological ideas to laboratory tests. Finally, we point out the relation between these schemes and the schemes suggested for quantum computing, teleportation, and quantum copying.     

Dissipative Dynamics of Quantum Discord of Two Strongly Driven Qubits

The exact dynamics of quantum discord (QD) of two strongly driven qubits, which are initially prepared in the X-type quantum states and inserted in two independent dissipative cavities or in a common dissipative cavity, are studied. The results indicate that both in the two cases, the evolution of QD is independent of the initial cavity state. For the two independent dissipative cavities, it is found that the phenomenon of sudden transition between classical and quantum decoherence exists and the transition time can be greatly delayed by suitably choosing the initial state parameter of the two qubits, the cavity mode-driving field detunning and the decay rate of the cavity. For the common dissipative cavity, it is shown that for some initial states of the two qubits, the QD can increase for a finite time at first, and then it decreases to a steady value, while for some other initial states, the QD can increase monotonously or with oscillation till a stable value is reached. Moreover, the creation of QD for the two qubits in a common cavity is discussed.     

Quantum State Preparation and Protection by Measurement-Based Feedback Control Against Decoherence

We consider an open quantum system subjected to a noise channel under measurement-based feedback control and two prototypical classes of decoherence channels are considered: phase damping and generalized amplitude damping. Based on quantum trajectory theory, we obtain an extended master equation for the dynamics of the reduced system in the presence of feedback control. For a qubit system we analytically solve this master equation and obtain the solution of the state vector dynamics. Then we propose an effective feedback control scheme for preparing an arbitrary quantum pure state. We also study how to protect two nonorthogonal states effectively, and find that projective measurement with unbiased basis is not optimal for this task, while weak measurement with biased basis could realize the best protection of two nonorthogonal states. Furthermore, the inefficiencies in the feedback process are also discussed.     

Entanglement Transfer Through Arrays of Cavities Coupled by Optical Fibers

We propose a scheme of entanglement transfer through two independent arrays of cavities coupled by optical fibers when each of the cavities contains a single two-level atom. We study the entanglement dynamics of the transferred states and find the explicit expression for the density matrix and concurrence. It is shown that the amount of the transferred entanglement has a direct connection with the target states and the lengths of the arrays of cavities. Moreover, the influence of the initial states and the length of the arrays of cavities on the phenomenon of entanglement sudden death is also investigated.     

Towards strongly correlated photons in arrays of dissipative nonlinear cavities under a frequency-dependent incoherent pumping

We report a theoretical study of a quantum optical model consisting of an array of strongly nonlinear cavities incoherently pumped by an ensemble of population-inverted two-level atoms. Projective methods are used to eliminate the atomic dynamics and write a generalized master equation for the photonic degrees of freedom only, where the frequency-dependence of gain introduces non-Markovian features. In the simplest single cavity configuration, this pumping scheme gives novel optical bistability effects and allows for the selective generation of Fock states with a well-defined photon number. For many cavities in a weakly non-Markovian limit, the non-equilibrium steady state recovers a Grand-Canonical statistical ensemble at a temperature determined by the effective atomic linewidth. For a two-cavity system in the strongly nonlinear regime, signatures of a Mott state with one photon per cavity are found.     

Entanglement of Two Atoms in Insulator and Superfluid States

We study two coupled cavities, each of which contains two two-level atoms. We identify the regions of Mott-insulator and superfluid states. Ground-state entanglement of two atoms in one cavity has been investigated. The result show that quantum entanglement of two atoms within one cavity can also characterize quantum phase transition.     

Transfer of quantum entangled states between superconducting qubits and microwave field qubits

Transferring entangled states between matter qubits and microwave-field (or optical-field) qubits is of fundamental interest in quantum mechanics and necessary in hybrid quantum information processing and quantum communication. We here propose a way for transferring entangled states between superconducting qubits (matter qubits) and microwave-field qubits. This proposal is realized by a system consisting of multiple superconducting qutrits and microwave cavities. Here, „qutrit” refers to a three-level quantum system with the two lowest levels encoding a qubit while the third level acting as an auxiliary state. In contrast, the microwave-field qubits are encoded with coherent states of microwave cavities. Because the third energy level of each qutrit is not populated during the operation, decoherence from the higher energy levels is greatly suppressed. The entangled states can be deterministically transferred because measurement on the states is not needed. The operation time is independent of the number of superconducting qubits or microwave-field qubits. In addition, the architecture of the circuit system is quite simple because only a coupler qutrit and an auxiliary cavity are required. As an example, our numerical simulations show that high-fidelity transfer of entangled states from two superconducting qubits to two microwave-field qubits is feasible with present circuit QED technology. This proposal is quite general and can be extended to transfer entangled states between other matter qubits (e.g., atoms, quantum dots, and NV centers) and microwave- or optical-field qubits encoded with coherent states.