Jiahua Li

Formation and ultraslow propagation of infrared solitons in graphene under an external magnetic field

Unusual dispersion relation of graphene nanoribbons for electrons can lead to an exceptionally strong optical response in the infrared regime and exhibits a very good tunable frequency. According to quantum optics and solid-material scientific principles, here we show the possibility to generate ultraslow infrared bright and dark solitons in graphene under the action of strong magnetic and infrared laser fields. By means of quantum-mechanical density-matrix formalism, we derive the equations of motion that govern the nonlinear evolution of the probe-pulse envelope in this scheme. It is found that, by properly choosing the parameters of the system, the formation and ultraslow propagation of infrared spatial solitons originate from the balance between nonlinear effects and the dispersion properties of the graphene under infrared excitation. Moreover, the unique electronic properties and selection rules near the Dirac point provide more freedom for us to study the linear and nonlinear dynamical responses of the photonics and graphene system. These results may have potential applications in telecommunication and optical information processing.

High-precision atom localization via controllable spontaneous emission in a cycle-configuration atomic system

A scheme for realizing two-dimensional (2D) atom localization is proposed based on controllable spontaneous emission in a coherently driven cycle-configuration atomic system. As the spatial-position-dependent atom-field interaction, the frequency of the spontaneously emitted photon carries the information about the position of the atom. Therefore, by detecting the emitted photon one could obtain the position information available, and then we demonstrate high-precision and high-resolution 2D atom localization induced by the quantum interference between the multiple spontaneous decay channels. Moreover, we can achieve 100% probability of finding the atom at an expected position by choosing appropriate system parameters under certain conditions.

Generation of Greenberger-Horne-Zeilinger state of distant diamond nitrogen-vacancy centers via nanocavity input-output process

An alternative scheme is proposed for the generation of an N-qubit Greenberger-Horne-Zeilinger (GHZ) state with distant nitrogen-vacancy (N-V) centers confined in spatially separated photonic crystal (PC) nanocavities via input-output process of photon. The GHZ state is produced by the phase shift brought by the input-output photon. The certain polarized photon transmitted from a PC nanocavity side-coupled a waveguide can obtain different phase shifts due to the different spin states in diamond N-V centers and the optical spin selection rule. Our calculations show that the proposed scheme can work well with a large cavity damping rate which ensures the efficient output of photon.

Iterative ghost imaging.

The recovered image in ghost imaging (GI) contains an error term when the number of measurements M is limited. By iteratively calculating the high-order error term, the iterative ghost imaging (IGI) approach reconstructs a better image, compared to one recovered using a traditional GI approach, without adding complexity. We first propose an experimental scheme, for which IGI can be realized, namely the narrowed point spread function and exponentially increased signal-to-noise ratio (SNR) are realized. The exponentially increasing SNR when implementing IGI results from the replacement of M with M(k). Thus, a perfect recovery of the unknown object is demonstrated with M slightly bigger than the number of speckles in a typical light field. Based on our theoretical framework from the angle of high-order correlation R(k), the two critical behaviors of the iterative coefficients α and the measurements M are derived and well explained.

Optomechanically induced transparency in the presence of an external time-harmonic-driving force

We propose a potentially valuable scheme to measure the properties of an external time-harmonic-driving force with frequency ω via investigating its interaction with the combination of a pump field and a probe field in a generic optomechanical system. We show that the spectra of both the cavity field and output field in the configuration of optomechanically induced transparency are greatly modified by such an external force, leading to many interesting linear and non-linear effects, such as the asymmetric structure of absorption in the frequency domain and the antisymmetry breaking of dispersion near ω = ωm. Furthermore, we find that our scheme can be used to measure the initial phase of the external force. More importantly, this setup may eliminate the negative impact of thermal noise on the measurement of the weak external force in virtue of the process of interference between the probe field and the external force. Finally, we show that our configuration can be employed to improve the measurement resolution of the radiation force produced by a weak ultrasonic wave.

Dynamical control of soliton formation and propagation in a Y-type atomic system with dual ladder-type electromagnetically induced transparency

We have investigated the nonlinear interaction between a weak-pulsed probe field and a four-level Y-type atomic system with dual ladder-type electromagnetically induced transparency. Two strong coupling fields induce a quantum destructive interference effect which depletes the population in the two nearly degenerate uppermost levels of the system and dramatically enhances the linear as well as nonlinear dispersion while simultaneously significantly suppressing the probe field absorption. We present the semiclassical quantum analysis of the system. The perturbation method of multiple scales is used to derive a differential envelope equation that describes the propagation of the probe field in the Y-type atomic system. It is then demonstrated that bright and dark optical solitons can be formed in this system.

Achieving maximum entanglement between two nitrogen-vacancy centers coupling to a whispering-gallery-mode microresonator

We investigate the entanglement generation between two nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a high-Q counterpropagating twin whispering-gallery modes (WGMs) of a microtoroidal resonator. For looking into the degree and dynamics of the entanglement, we calculate the concurrence using the microscopic master equation approach. The influences of the coupling strength between the WGMs (or the size of the two spherical NV centers), the distance between two NV centers, the frequency detuning between the NV center and microresonator, and the initial state of the system on the dynamics of concurrence are discussed in detail. It is found that the maximum entanglement between the two NV centers can be created by properly adjusting these controllable system parameters. Our results may provide further insight into future solid-state cavity quantum electrodynamics (CQED) system for quantum information engineering.

Propagation of twin light pulses under magneto-optical switching operations in a four-level inverted-Y atomic medium

Propagation dynamics of twin laser pulses through a cold four-level inverted-Y atomic medium is investigated theoretically via switching on and off an external magnetic field under the application of a strong driving field. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously on a spacetime grid, our spatio-temporal results clearly show that dynamic control of twin-pulse propagation and magneto-optic dual switching operation are possible in such an inverted-Y system. The proposed scheme may be used for the design of magneto-optic switching and magneto-optic storage devices.

Generation of a multi-qubit W entangled state through spatially separated semiconductor quantum-dot-molecules in cavity-quantum electrodynamics arrays

Generating entangled states attract tremendous interest as the most vivid manifestation of nonlocality of quantum mechanics and also for emerging applications in quantum information processing (QIP). Here, we propose theoretically a scheme for the deterministic generation of a three-qubit W sate with three semiconductor quantum-dot-molecules (QDMs) trapped in spatially separated cavities connected by optical fibers. The proposed scheme takes full advantage of the voltage-controlled tunnelling effects in QDMs, which induces the quantum coherence and further controls the generation of the W entangled state. The influences of the system parameters and various decoherence processes including spontaneous decay and photon leakage on the fidelity of the W state are discussed in details. Numerical results indicate that our scheme is not only robust against these decoherence factors but also insensitive to the deviation of the system parameters from the ideal conditions. Furthermore, the present scheme can be dire...

Creation of quantum entanglement with two separate diamond nitrogen vacancy centers coupled to a photonic molecule

We explore the entanglement generation and the corresponding dynamics between two separate nitrogen-vacancy (NV) centers in diamond nanocrystal coupled to a photonic molecule consisting of a pair of coupled photonic crystal (PC) cavities. By calculating the entanglement concurrence with readily available experimental parameters, it is found that the entanglement degree strongly depends on the cavity-cavity hopping strength and the NV-center-cavity detuning. High concurrence peak and long-lived entanglement plateau can be achieved by properly adjusting practical system parameters. Meanwhile, we also discuss the influence of the coupling strength between the NV centers and the cavity modes on the behavior of the concurrence. Such a PC-NV system can be employed for quantum entanglement generation and represents a building block for an integrated nanophotonic network in a solid-state cavity quantum electrodynamics platform. In addition, the present theory can also be applied to other similar systems, such as two single quantum emitters positioned close to a microtoroidal resonator with the whispering-gallery-mode fields propagating inside the resonator.