Second-order magnetic field gradient-induced strong coupling between nitrogen-vacancy centers and a mechanical oscillator

We consider a cantilever mechanical oscillator (MO) made of diamond. A nitrogen-vacancy (NV) center lies at the end of the cantilever. Two magnetic tips near the NV center induce a strong second-order magnetic field gradient. Under coherent driving of the MO, we find that the coupling between the MO and the NV center is greatly enhanced. We studied how to generate entanglement between the MO and the NV center and realize quantum state transfer between them. We also propose a scheme to generate two-mode squeezing between different MO modes by coupling them to the same NV center. The decoherence and dissipation effects for both the MO and the NV center are numerically calculated using the present parameter values of the experimental configuration. We have achieved high fidelity for entanglement generation, quantum state transfer, and large two-mode squeezing.     

Long-distance quantum state transfer through cavity-assisted interaction

We propose a scheme for long-distance quantum state transfer between different atoms based on cavity-assisted interactions. In our scheme, a coherent optical pulse sequentially interacts with two distant atoms trapped in separated cavities. Through the measurement of the state of the first atom and the homodyne detection of the final output coherent light, the quantum state can be transferred into the second atom with a success probability of unity and a fidelity of unity. In addition, our scheme neither requires the high-Q cavity working in the strong coupling regime nor employs the single-photon quantum channel, which greatly relaxes the experimental requirements.     

Scheme for Implementing Quantum Dense Coding and Teleportation with Tripartite Entangled State in Cavity QED

In this paper, we present a peculiar tripartite entangled state that is inequivalent to both the GHZ state and the W state, and then propose to implement efficient quantum information processing such as quantum dense coding and teleportation with this entangled state in cavity QED. In this scheme the atoms interact with a highly detuned cavity field with the assistance of a strong classical driven field. It does not require the transfer of quantum information between the atomic system and the cavity, and then our scheme is insensitive to both the cavity decay and the thermal field.     

Dissipation-induced topological phase transition and periodic-driving-induced photonic topological state transfer in a small optomechanical lattice

We propose a scheme to investigate the topological phase transition and the topological state transfer based on the small optomechanical lattice under the realistic parameters regime.We find that the optomechanical lattice can be equivalent to a topologically nontrivial Su-Schrieffer Heeger(SSH)model via designing the effective optomechanical coupling.Especially,the optomechanical lattice experiences the phase transition between topologically nontrivial SSH phase and topologically trivial SSH phase by controlling the decay of the cavity field and the opto mechanical coupling.We stress that the to pological phase transition is mainly induced by the decay of the cavity field,which is counter-intuitive since the dissipation is usually detrimental to the system.Also,we investigate the photonic state transfer between the two cavity fields via the topologically protected edge channel based on the small optomechanical lattice.We find that the quantum st ate transfer assisted by the topological zero energy mode can be achieved via implying the external lasers with the periodical driving amplitudes into the cavity fields.Our scheme provides the fundamental and the insightful explanations towards the mapping of the photonic topological insulator based on the micro-nano optomechanical quantum optical platform.     

Bose-Einstein condensate coupled to a nanomechanical resonator on an atom chip

We theoretically study the coupling of Bose-Einstein condensed atoms to the mechanical oscillations of a nanoscale cantilever with a magnetic tip. This is an experimentally viable hybrid quantum system which allows one to explore the interface of quantum optics and condensed matter physics. We propose an experiment where easily detectable atomic spin flips are induced by the cantilever motion. This can be used to probe thermal oscillations of the cantilever with the atoms. At low cantilever temperatures, as realized in recent experiments, the backaction of the atoms onto the cantilever is significant and the system represents a mechanical analog of cavity quantum electrodynamics. With high but realistic cantilever quality factors, the strong coupling regime can be reached, either with single atoms or collectively with Bose-Einstein condensates. We discuss an implementation on an atom chip.     

Quantum information transfer and entanglement with SQUID qubits in cavity QED: a dark-state scheme with tolerance for nonuniform device parameter

We investigate the experimental feasibility of realizing quantum information transfer (QIT) and entanglement with SQUID qubits in a microwave cavity via dark states. Realistic system parameters are presented. Our results show that QIT and entanglement with two-SQUID qubits can be achieved with a high fidelity. The present scheme is tolerant to device parameter nonuniformity. We also show that the strong coupling limit can be achieved with SQUID qubits in a microwave cavity. Thus, cavity-SQUID systems provide a new way for production of nonclassical microwave source and quantum communication.     

A scheme for transferring an unknown atomic entangledstate via cavity quantum electrodynamics

In this paper, we propose a scheme for transferring an unknown atomic entangled state via cavity quantum electrodynamics (QED). This scheme, which has a successful probability of 100 percent, does not require Bell-state measurement and performing any operations to reconstruct an initial state. Meanwhile, the scheme only involves atom--field interaction with a large detuning and does not require the transfer of quantum information between the atoms and cavity. Thus the scheme is insensitive to the cavity field states and cavity decay. This scheme can also be extended to transfer ring an entangled state of $n$-atom.     

电子自旋辅助实现光子偏振态的量子纠缠浓缩

量子纠缠浓缩可以将非最大的纠缠态转变为最大纠缠态,提高量子通信的安全性.本文基于圆偏振光和量子点-腔系统的相互作用,用一个单光子作为连接远距离纠缠光子对的桥梁,在理想条件下实现了光子偏振纠缠态的浓缩.计算结果显示,这个纠缠浓缩方案在考虑耦合强度和腔泄漏的情况下也可以保持较高的保真度,而且不需要知道部分纠缠态的初始信息,也不必重复执行纠缠浓缩过程.这不仅提高了量子纠缠浓缩的安全性,也有助于通过消耗最少的量子资源来实现高效的量子信息处理.     

利用腔QED实现量子态转移

利用两个二能级原子和用光纤联接的两个单模光腔构成的系统,给出了实现量子态转移的方案。该方案中两个二能级原子分别处于用光纤联接的单模腔中,并同时与光场发生共振相互作用。通过控制原子与光场的相互作用时间,实现量子态的转移。     

利用腔QED实现量子态转移

利用两个二能级原子和用光纤联接的两个单模光腔构成的系统,给出了实现量子态转移的方案。该方案中两个二能级原子分别处于用光纤联接的单模腔中,并同时与光场发生共振相互作用。通过控制原子与光场的相互作用时间,实现量子态的转移。     

Efficient atomic quantum memory for photonic qubits in cavity QED

We investigate a scheme of atomic quantum memory to store photonic qubits of polarization in cavity QED. It is observed that the quantum state swapping between a single-photon pulse and a Λ-type atom can be made via scattering in an optical cavity [T. W. Chen, C. K. Law, P. T. Leung, Phys. Rev. A 69 (2004) 063810]. This swapping operates limitedly in the strong coupling regime for Λ-type atoms with equal dipole couplings. We extend this scheme in cavity QED to present a more feasible and efficient method for quantum memory combined with projective measurement. This method works without requiring such a condition on the dipole couplings. The fidelity is significantly higher than that of the swapping, and even in the moderate coupling regime it reaches almost unity by narrowing sufficiently the photon-pulse spectrum. This high performance is rather unaffected by the atomic loss, cavity leakage or detunings, while a trade-off is paid in the success probability for projective measurement.     

Controlled Quantum State Transfer with Separate Measurements in Cavity QED

An experimental scheme on controlled quantum state transfer is proposed in cavity quantum electrodynamics (QED) without joint Bell-state measurement (BSM). A quantum state can be transferred perfectly with the help of the cooperation of the third side by constructing a three-atom GHZ entangled state as the controlled channel. This scheme is insensitive to the cavity decay and the thermal field. The probability of the success in our scheme is 1.0.     

Schemes for Generating Cluster States via Cavity Systems

We propose a scheme for generating an N-atom cluster state via cavity quantum electrodynamics （ CQED）. In our scheme, there is no transfer of quantum information between the atoms and the cavity, i.e., the cavity is always in the vacuum state, so the cavity decay can be suppressed. Also, the generated cluster state is the entanglement of the ground states, so the atomic spontaneous emission can be avoided. Therefore, the cluster state generated in our scheme has a longer lifetime. Furthermore, the requirement on the quality factor of the cavity greatly loosened for the cavity is only virtually excited.     

Preparation of the four-qubit cluster states in cavity QED and the trapped-ion system

This paper proposes a simple scheme to generate a four-atom entangled cluster state in cavity quantum electrodynamics. With the assistantce of a strong classical field the cavity is only virtually excited and no quantum information will be transferred from the atoms to the cavity during the preparation for a four-atom entangled cluster state, and thus the scheme is insensitive to the cavity field states and cavity decay. Assuming that deviation of laser intensity is 0.01 and that of simultaneity for the interaction is 0.01, it shows that the fidelity of the resulting four-atom entangled cluster state is about 0.9886. The scheme can also be used to generate a four-ion entangled cluster state in a hot trapped-ion system. Assuming that deviation of laser intensity is 0.01, it shows that the fidelity of the resulting four-ion entangled cluster state is about 0.9990. Experimental feasibility for achieving this scheme is also discussed.     

A simple scheme for generating multi-atom GHZ state via cavity QED

This paper proposes a simple scheme for generating a three-atom GHZ state via cavity quantum electrodynamics (QED). The task can be achieved through the interaction between two EPR states, which can be prepared easily with current technology. In this scheme, the cavity field is only virtually excited during the interaction process, and no quantum information transfer between the atoms and the cavity is required. Thus it greatly prolongs the efficient decoherent time. Moreover, this scheme is also applicable for generating an N-atom GHZ state.     

An Alternative Scheme for Transferring Quantum States and Preparing a Quantum Network in Cavity QED

An alternative scheme is proposed to transfer quantum states and prepare a quantum network in cavity QED. It is based on the interaction of a two-mode cavity field with a three-level V-type atom. In the scheme, the atom-cavity field interaction is resonant, thus the time required to complete the quantum state transfer process is greatly shortened, which is very important in view of decoherence. Moreover, the present scheme does not require one mode of the cavities to be initially prepared in one-photon state, thus it is more experimentally feasible than the previous ones.     

Entanglement transfer from two-mode squeezed vacuum light to spatially separated mechanical oscillators via dissipative optomechanical coupling

In this paper, we propose a scheme to generate an entangled state between two spatially separated movable mirrors by injecting the two-mode squeezed optical reservoir to the dissipative optomechanics, in which the movable mirrors can modulate the linewidth of the cavity modes. When the coupling between the mirrors and the corresponding cavity modes is weak, the two driven cavity fields can respectively behave as the squeezed-vacuum reservoir for the two movable mirrors by utilizing the effect of completely destructive interference of quantum noise. Thus the mechanical modes are prepared in a two-mode squeezed vacuum state. Moreover,when the coupling between the two mirrors and the cavities modes is strong, the entanglement between the two movable mirrors decreases because photonic excitation can preclude the completely destructive interference of quantum noise, but the movable mirrors are still entangled.     

传送两原子直积态的腔QED方案(英文)

本文提出一个基于原子和腔场共振相互作用传送未知原子直积态的腔QED方案,原子和腔场通过J-C哈密顿量发生共振相互作用.在这个方案里,我们只需要用两个原子接受被传送的原子态以及两个单模腔作为量子通道.该方案既不需要贝尔态测量,也不需要任何操作重构纠缠初态,并且传送成功的概率为100%.这个方案也可以推广到传送n个原子的直积态.     

Virtual-Excitation Induced High-Dimensional State Transfer in a Quantum Network

We propose a scheme for quantum state transfer within the high-dimensional state subspaces between any two nodes in a quantum network. The states are encoded in the collective ground states of multiple atoms. The transfer processes are controlled by only applying external laser pulses. The prominent feature of the scheme is that the state transfer of any dimension can be achieved through virtually coupling all the excitations of the total system.     

Deterministic CNOT gate and entanglement swapping for photonic qubits using a quantum-dot spin in a double-sided optical microcavity

Abstract We propose a deterministic and scalable scheme to construct a two-qubit controlled-NOT (CNOT) gate and realize entanglement swapping between photonic qubits using a quantum-dot (QD) spin in a double-sided optical microcavity. The scheme is based on spin selective photon reflection from the cavity and can be achieved in a nondestructive and heralded way. We assess the feasibility of the scheme and show that the scheme can work in both the weak coupling and the strong coupling regimes. The scheme opens promising perspectives for long-distance photonic quantum communication and distributed quantum information processing.