Teleportation of N-qubit W State without Bell-State Measurement via Selective Resonant Interaction in Cavity QED

We present a scheme in which the N-atom W state is teleported by employing the selective interactionof a cavity field with a driven three-level atom in the A configuration and detecting a single atom in one of the groundstates.The long-lived W state is teleported from atom A to atom B when the atoms B and A are sent through acavity successively and atom A is then detected.The advantage is that the present one does not involve the Bell-statemeasurement and is robust against the atomic spontaneous emission.

Influence of the Stark Shift on Entanglement Sudden Death and Birth in Cavity QED

＊Supported by the National Natural Science Foundation of China under Grant No 11065007 and 11047115, the Natural Science Foundation of Jiangxi Province under Grant Nos 2007GZW0819 and 2008GQW0017, the Scientific Research Foundation of Jiangxi Provincial Department of Education under Grant Nos G J J09504 and G J J10135, and the Foundation of Talent of Jinggang of Jiangxi Province under Grant No 2008DQ00400.

Two-Qubit Logic Gates and Teleportation of an Entangled State of Atom-Cavity with Cavity QED

In this paper, a scheme is proposed for realization of two-qubit controlled-not gates and teleportation of an entangled state of atom-cavity. In this scheme, applying hyperfine levels of atom, we consider A-type three-level atom interacting resonantly or nonresonantly with cavity field that is prepared in σ- polarized. We consider the experimental feasibility of this scheme and compare our results with other schemes.

Influences of control coherence and decay coherence on optical bistability in a semiconductor quantum well

We discuss the influences of two different types of mechanisms of quantum coherence on optical bistability in a semiconductor quantum well structure.In the first mechanism,only quantum coherence induced by the resonant coupling of a strong control laser is considered.In the second mechanism,the decay coherence is taken into account under the condition where the control field is weak.In two different cases,optical bistability can be obtained through choosing appropriate physical parameters.Our studies show quantum coherence makes the optical nonlinear effect of the system become stronger,which takes an important role in the process of generating optical bistability.A semiconductor quantum well with flexibility and easy integration in design could potentially be exploited in real solid-state devices.

Distillation of bi-partite entanglement from W state with cavity QED

Following the theoretical protocol described by Fortescue and Lo [Fortescue B and Lo H K 2007 Phys. Rev. Lett. 98 2605011, we present a scheme in which one can distill maximally entangled bi-partite states from a tri-partite W state with cavity QED. Our scheme enables the concrete physical system to realize its protocol. In our scheme, the rate distillation also asymptotically approaches one. Based on the present cavity QED techniques, we discuss the experimental feasibility.

Analytical Expression of Ground State of Double-Well Bose-Einstein Condensates

We derive an approximate analytical expression for the ground state of double-well BEC＇s, which reproduces highly accurately the numerical solution for the whole parameter regimes of the two-body repulsive interaction strength, the total number of atoms, and the hopping parameter.

Preparation of steady-state entanglement via a laser-excited resonant interaction

In this paper we propose a scheme in which two-mode entanglement in a steady state is produced by using two lasers to resonantly drive a single four-level atom embedded inside a two-mode optical cavity. In this scheme, atomic coherence induced by a classical laser plays an important role in the process of preparing the entangled state. With the coupling of a strong control field, direct two-photon transition is generated and the relatively weak pump field induces the parametric interaction between two photons, which makes them entangle with each other. By numerical calculation, we find that the degree of entanglement depends strongly on the Rabi frequencies of the classical laser fields and the cavity losses.

Absorption and slow light effect of pulsed light in a triple semiconductor quantum well

Under the condition of two different cases, the absorption of a pulsed probe field and its slow propagation in a triple semiconductor quantum well are investigated. The result shows that semiconductor medium becomes transparent due to the action of control field. Another result shows that by choosing appropriate physical parameters, the slow propagation of the input field can be achieved. The proposed scheme has some potential applications and may lead to the development of the controlled technique of optical buffers and optical delay lines.

Spin-and valley-polarized Goos–Hänchen-like shift in ferromagnetic mass graphene junction with circularly polarized light

We investigate the band structure and Goos–Hänchen-like shift in ferromagnetic mass graphene junction modulated by the circularly polarized light.It is found that both spin and valley-related energy gaps can be opened by employing the circularly polarized light and the exchange field in mass graphene.The valley-polarized Goos–Hänchen-like shift can be identified in the presence of circularly polarized light,and the spin-polarized Goos–Hänchen-like shift can be realized with introduction of exchange field in mass graphene.Furthermore,the spin and valley polarization-related Goos–Hänchen-like shift can be achieved by combination of circularly polarized light and exchange field in mass graphene.It is hopeful that our work will be more conducive for future applications in graphene polarization transport devices.

Optical bistability and multistability in a three-level △-type atomic system under the nonresonant condition

Under a nonresonant condition, we theoretically investigate hybrid absorptive-dispersive optical bistability and multistability behaviours in a three-level △-type system by using a microwave field to drive a hyperfine transition between two upper excited states inside a unidirectional ring cavity. We find that the optical bistability and multistability behaviours can be controlled by adjusting the intensity of the microwave field or the intensity of the coherent coupling field. Furthermore, our studies show an interesting phenomenon of the transition from the optical bistability to the optical multistability only by changing the negative detuning of the coupling field into the positive detuning of the coupling field.

Vacuum induced transparency and slow light phenomena in a two-level atomic ensemble controlled by a cavity

We study the optical properties of a two-level atomic ensemble controlled by a high-finesse cavity. Even though the cavity is initially in the vacuum state in the absence of external driving, the probe response of the atomic ensemble can be dramatically modified. When the collectively enhanced atom–cavity coupling is strong enough and the cavity decay rate is much smaller than the atomic damping rate, an electromagnetically induced transparency-like coherent phenomenon emerges with a dip absorption for the response of the two-level atoms in the cavity without driving, and thus is called vacuum induced transparency. We also show the slow light with very low group velocity in such an atomic ensemble.

High effcient scheme for remote state preparation with cavity QED

In this paper, a scheme is proposed for remote state preparation （RSP） with cavity quantum electrodynamics （QED）. In our scheme, two observers share two-atom nonmaximally entangled state as quantum channels and can realize remote preparation of state of an atom. We also propose a generalization for remote preparation of N-atom entangled state by （N＋1）-atom GHZ-like state （N ≥ 2）. By this scheme, one single-atom projective measurement is enough for the RSP of a qubit or N-atom entangled state, and the probability of success for RSP is unity. Furthermore, we have considered the case where observers use W-like state as quantum channels to realize RSP of a qubit. We compare our scheme with existing ones.

Unconventional geometric phase gate and multiqubit entanglement for hot ions with a frequency-modulated field

We present an alternative scheme for implementing the unconventional geometric two-qubit phase gate and prepar- ing multiqubit entanglement by using a frequency-modulated laser field to simultaneously illuminate all ions. Selecting the index of modulation yields selective mechanisms for coupling and decoupling between the internal and the external states of the ions. By the selective mechanisms, we obtain the unconventional geometric two-qubit phase gate, multiparticle Greenberger-Horne-Zeilinger states and highly entangled cluster states. Our scheme is insensitive to the thermal motion of the ions.

Weak-Coupling Theory for Low-Frequency Periodically Driven Two-Level Systems

We generalize the Wu-Yang strong-coupling theory to solve analytically periodically driven two-level systems in the weak-coupling and low-frequency regimes for single- and multi-period periodic driving of continuous-wave-type and pulse-type including ultrashort pulses of a few cycles.We also derive a general formula of the AC Stark shift suitable for such diverse situations.

Remote Operation on Quantum State Among Multiparty

In this paper, a scheme is proposed for performing remote operation on quantum state among multiparty. We use three-particle GHZ state as quantum channels to prepare a state operator, which describes quantum correlation between states and operations. Based on the special characteristic of the state operator, observers can perform unitary operation on a system that is away from observers. Our studies show this process is deterministic. We further consider remote operation among N spatially distributed observers, and the results show the successful realization of remote operation needs collective participation of N parties, that is, there exists strong correlation among multiparty. In addition, we investigate the case in which observers share a three-particle W state as quantum channels to perform remote operation and studies find this process is probabilistic.

Phase-controlled coherent population trapping in superconducting quantum circuits

We investigate the influences of the-applied-field phases and amplitudes on the coherent population trapping behavior in superconducting quantum circuits. Based on the interactions of the microwave fields with a single A-type three-level fluxonium qubit, the coherent population trapping could be obtainable and it is very sensitive to the relative phase and amplitudes of the applied fields. When the relative phase is tuned to 0 or π, the maximal atomic coherence is present and coherent population trapping occurs. While for the choice of π/2, the atomic coherence becomes weak. Meanwhile, for the fixed relative phase π/2, the value of coherence would decrease with the increase of Rabi frequency of the external field coupled with two lower levels. The responsible physical mechanism is quantum interference induced by the control fields, which is indicated in the dressed-state representation. The microwave coherent phenomenon is present in our scheme, which will have potential applications in optical communication and nonlinear optics in solid-state devices.

Ultraslow optical solitons in tunnel-coupled double semiconductor quantum well

This paper investigates the nonlinear evolution of the pulse probe field in an asymmetric coupled-quantum well driven coherently by a pulse probe field and two controlled fields. This study shows that, by choosing appropriate physical parameters, self-modulation can precisely balance group velocity dispersion in the investigated system, leading to the formation of ultraslow optical solitons of the probe field. The proposed scheme may lead to the development of the controlled technique of optical buffers and optical delay lines.

High-efficiency asymmetric diffraction based on PT-antisymmetry in quantum dot molecules

We present preparation of asymmetric grating with higher diffraction efficiency in quantum dot molecules by combining the tunneling effect and parity-time antisymmetry.In the presence of tunneling between two quantum dots,the system exhibits the striking PT antisymmetry via spatially modulating the driving field and the detuning with respect to the driven transition.For this reason,the asymmetric grating could be achieved.The results show that the diffraction efficiency can be adjustable via changing the driving intensity,detuning,tunneling strength,and interaction length,and then the high-order diffraction can be reached.The scheme provides a feasible way to obtain the direction-controlled diffraction grating,which can be helpful for optical information processing and realization of controllable optical self-image.

Goos-Hanchen-like shift related to spin and valley polarization in ferromagnetic silicene

We study the Goos-Hanchen-like shift of single silicene barrier under the external perpendicular electric field,off- resonant circularly polarized light and the exchange field modulation using the stationary-phase method.The results show that the Goos-Hanchen-like shift of silicene resulting from the external perpendicular electric field does not have the characteristics of spin or valley polarization,while that from off-resonant circularly polarized light or the exchange field is spin-polarized.More importantly,the combined effect of the external perpendicular electric field and the exchange field or off-resonant circularly polarized light can cause the Goos-Hanchen-like shift of the system to be spin and valley polarized.It is particularly worth noting that when the three modulations are considered at the same time,as the exchange field changes,the system will have a positive or negative Goos-Hanchen-like shift.

Exact analytical solution for quantum spins mixing in spin-1 Bose-Einstein condensates

This paper solves exactly a set of fully quantized coupled equations describing the quantum dynamics of quantum spins mixing in spin-1 Bose-Einstein condensates by deriving the exact explicit analytical expressions for the evolution of creation and annihilation operators.