Preparation of Highly Squeezed States and Multi—component Entangled Coherent States via the Raman Interaction

A method is presented for generating highly squeezed states of a cavity field via the atom-cavity field interaction of the Raman type.In the scheme a sequence of three-level Λ-type atoms interacts with a cavity field,displaced by a classical source,in a Raman manner.Then the atomic states are measured.By this way the cavity field may collapse onto a superposition of several coherent states,which exhibits strong squeezing.The scheme can also be used to prepare superpositions of many two-mode coherent states for two cavity fields.The coherent states in each mode are on a straight line.This is the first way for preparing multi-component entangled coherent states of this type in cavity QED.     

好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度

考虑原子间偶极相互作用,求出好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度。结果表明,对于理想腔,若原子初始时刻处于相干保持态,系统保真度始终等于1;若原子初始时刻处于其余Bell态之一,腔场初态的平均光子数很小,系统保真度在0～1之间作周期性振荡,随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小。对于好腔,若原子初始时刻处于相干保持态,系统保真度呈指数单调衰减;若原子初始时刻处于其余Bell态之一,系统保真度呈指数振荡衰减,且随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小。     

好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度

考虑原子间偶极相互作用,求出好腔中的Bell态原子与纠缠相干态光场相互作用系统的保真度.结果表明,对于理想腔,若原子初始时刻处于相干保持态,系统保真度始终等于1;若原子初始时刻处于其余Bell态之一.腔场初态的平均光子数很小,系统保真度在0～1之间作周期性振荡,随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小.对于好腔,若原子初始时刻处于相干保持态,系统保真度呈指数单调衰减;若原子初始时刻处于其余Bell态之一,系统保真度呈指数振荡衰减,且随着腔场初态的平均光子数的增加,系统保真度的振荡频率增大,振幅减小.     

Generation of pair cat states through two-mode degenerate Raman process

We propose a scheme for generating superpositions of two pair coherent states of a two-mode field. In the scheme an atom is sent through a cavity initially in a pair coherent state. The state-selective measurement following the two-mode Raman process projects the two-mode field to a pair cat state.     

Generation of entangled coherent states for two cavity modes via resonant interaction with a V-type three-level atom

This paper proposes a scheme for the generation of entangled coherent states for two cavity modes. In the scheme a V-type three-level atom is sent through a two-mode cavity filled with a coherent field. After the atom cavity interaction and detection of the atomic state the cavity modes may evolve to a superposition of two-mode coherent states. As the scheme is based on resonant atom-cavity interaction, the required interaction time is short, which is important in view of the decoherence. Moreover, additional classical pulses are unnecessary before and after the atom-cavlty interaction.     

Probabilistic Teleportation of an Arbitrary Two-mode <Emphasis Type="Italic">N</Emphasis>-photon Entangled State in Cavity QED

We propose a scheme for teleportation of an arbitrary two-mode N-photon entangled states in cavity QED. The scheme is based on the resonant interaction between Λ-type atoms and two-mode cavity fields. In contrast to all the theoretical schemes proposed previously in cavity QED for teleportation of two-mode cavity field states, in the present scheme, the established entanglement for the quantum channel is the type of the multi-dimensional entanglement between the symmetric multi-atom Dicke states and two-mode N-photon states. Therefore, the scheme extends the scope of the theoretical study of the teleportation.     

Conditional Synthesis of Entangled Coherent States with Continuous External Pumping in a Dispersive Cavity QED

The interaction of $N$ two-level atoms with both a two-mode cavity field and an external classical pumping field, and with the fields being degenerate in frequency, is studied in the regime where the atoms and fields are highly detuned. This dispersive interaction can be used to generate a large number of important entangled coherent states conditional on the initial atomic states and state-selective measurements. A dynamical relation is established between the results for the case with continuous pumping and the case without external driving where the coherent field is put in as the initial condition.     

增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备

分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备.     

利用V-型三能级原子与双模腔场双光子大失谐相互作用制备W纠缠态

本文提出利用V-型三能级原子与双模腔场的双光子大失谐相互作用制备W纠缠态,该方案要求三个三能级原子和一个双模腔场,第一个与腔场作用的原子最初处于激发态,第二个和第三个原子均处于基态,腔场最初处于真空态,合适地选择原子与腔场之间的相互作用时间即可获得三原子W纠缠态.并且此方案可以推广至多原子W纠缠态和多腔场W纠缠态的制备;通过计算共生纠缠度研究系统中态的纠缠演化以及热纠缠现象.     

利用V-型三能级原子与双模腔场 双光子大失谐相互作用制备W纠缠态

本文提出利用 型三能级原子与双模腔场的双光子大失谐相互作用制备W纠缠态,该方案要求三个三能级原子和一个双模腔场,第一个与腔场作用的原子最初处于激发态,第二个和第三个原子均处于基态,腔场最初处于真空态,合适地选择原子与腔场之间的相互作用时间即可获得三原子W纠缠态。并且此方案可以推广至多原子W纠缠态和多腔场W纠缠态的制备;通过计算共生纠缠度研究系统中态的纠缠演化以及热纠缠现象。     

增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备

分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备.     

Transferring of a Two-Mode Entangled State Between Two Cavities via Cavity QED

We propose a scheme for transferring of a two-mode entanglement of zero- or one-photon entangled states between two cavities via atom-cavity field resonant interaction. In our proposal, in order to transfer the entangled state, we only need two identical two-level atoms and a two-mode cavity for receiving the teleported state. This scheme does not require Bell-state measurement and performing any transformations to reconstruct the initial state. And the transfer can occur with 100% success probability in a simple manner. And a network for transferring of a two-mode entangled state between cavities is suggested. This scheme can also be extended to transfer N-mode entangled state of cavity.     

"两原子-双模腔场"系统的腔场谱

研究了存在偶极相互作用的两等同原子与双模腔场共振相互作用双光子过程的腔场谱,研究发现,当两模初态都为光子数态或相干态时,两模腔场谱之间有很强的相互影响,在两模场强相同时,两划的光谱结构也相同,且在强场下呈现三峰结构;当两模初态场强不同时,较强的一模出现简单的单峰结构,而较弱模光谱中三峰的距离随另一模光子数的增加而增大。当两模均为压缩真空态时,在强场下得到经典共振荧光谱,且两模腔场谱之间的相互影响很弱。     

Preparation of W state in resonant bimodal cavity quantum electrodynamics

A scheme is proposed for generating entangled W states with four cavity modes. In this scheme, we send a V-type three-level atom through two identical two-mode cavities in succession. After the atom exits from the second cavity, the four cavity modes are prepared in the W state. On the other hand we can obtain three-atom W states by sending three V-type three-level atoms through a two-mode cavity in turn. The present scheme does not require conditional measurement, and it is easily generalized to preparing $2n$-mode W states and $n$-atom W states.     

Efficient scheme for the preparation of arbitrary anticorrelated states of a two-mode field

A scheme is presented for generating any anticorrelated state of a two-mode field. In the scheme a sequence of suitably prepared three-level V-type atoms are sent across a two-mode cavity initially in the vacuum state. The detection of all the atoms in the ground state collapses the two-mode field to the desired state.     

Scheme for Preparation of Macroscopic Multi-component Entanglement in Cavity QED

We propose a scheme of generating multi-component entangled coherent states of cavity fields. In this scheme, the atoms pass through cavities one by one, simultaneously driven by a strong classical field in each cavity. Then the detection of the atomic states collapses the cavity fields onto multi-component entangled coherent states. It is shown that, with a judicious choice of the parameters of the classical field, we can conditionally produce macroscopic multi-dimensional maximal entanglement for the cavity modes.     

Generation of Superpositions of Coherent Interaction States Along a Straight Line via Raman Interaction

We present an alternative scheme for preparing the superpositions of coherent states along a straight line of a cavity field using degenerate atom-cavity field Raman interaction. In the scheme, a collection of A-type three-level atoms is orderly sent through the cavity to interact with the cavity field adjusted by a microwave source connected to it, followed by state-selective measurements. In this way, we can prepare the superpositions of several coherent states along a straight line with arbitrary weighting factors for the cavity field. In the scheme, the coherence of the atom-cavity system may be maintained and the second microwave field is unnecessary, which is prior to the previous scheme.     

Generation of Superpositions of Coherent States Along a Straight Line via Raman Interaction

We present an alternative scheme for preparing the superpositions of coherent states along a straight line of a cavity field using degenerate atom-cavity field Raman interaction. In the scheme, a collection of A-type three-level atoms is orderly sent through the cavity to interact with the cavity field adjusted by a microwave source connected to it, followed by state-selective measurements. In this way, we can prepare the superpositions of several coherent states along a straight line with arbitrary weighting factors for the cavity field. In the scheme, the coherence of the atom-cavity system may be maintained and the second microwave field is unnecessary, which is prior to the previous scheme.     

通过Raman相互作用制备三个腔场的W型纠缠相干态

通过对比分立变量量子信息过程和连续变量量子信息过程的差别,利用相干态比较容易获得的这个特点,提出一种方案制备三个腔场的W型纠缠相干态.方案基于Λ型三能级原子与单模腔场的简并Raman 相互作用.三个相同的腔初始分别处于相干态,三个相同的原子初始处于W型纠缠态,通过三个原子分别与三个腔的Raman相互作用、选择适当的相互作用时间并探测作用后的三个原子,三个腔场坍缩为W型纠缠相干态.在原子与腔的相互作用过程中原子不处于高能级,可以忽略原子的自发辐射,系统的相干性能够得到较好的维持.基于当前的腔量子电动力学技术,相信方案能在实验上实现.该方案制备的三个腔场W型纠缠相干态有望在连续变量量子信息过程中有重要的应用价值.文中将方案推广到制备n(n〉3)个腔场的W型纠缠相干态.     

Production of three-dimensional entanglement for two atoms with a single resonant interaction

A scheme is proposed for generating three-dimensional maximally entangled states for two atoms. In the scheme the atoms are trapped in a two-mode cavity. The scheme only requires a single resonant interaction of the atoms with the cavity modes. Therefore, the scheme is very simple and required interaction time is very short, which is important in view of decoherence.