摘要：
A new scheme for three-dimensional (3D) atom localization is proposed based on measuring the probe absorption spectra in a four-level diamond-configuration atomic system, in which the atom interacts with three orthogonal standing-wave laser fields. Due to spatial-dependent interaction between atom and fields, position information of the atom can be obtained by measuring the absorption spectra of the weak probe field. The results show that atom localization properties can be significantly improved and some interesting spatial localization structures such as double-layer lantern-like, single-layer lantern-like, gourd-like, cylinder-like, and ellipsoid-like patterns can be achieved when we adjust system parameters properly. Most importantly, we can find the atom at a particular position in 3D space with 100% probability under appropriate conditions.
摘要：
In this paper, we carry out a theoretical investigation on the population dynamics of graphene system under continuous-wave (cw) laser and chirped pulse excitation. Results of our numerical simulations reveal that complete population transfer from an initially occupied ground state to the initially unoccupied excited states can be achieved by choosing appropriate values of the chirp rate, the laser field intensity and frequency, as well as other system parameters. Also, we observe coherent Rabi-like population oscillations between the initial ground state and the excited final state. It is induced by the combined effect of cw and chirped-pulse laser fields. These results will contribute to the understanding of carrier-carrier and carrier-phonon interactions in graphene system, and may find applications in graphene-based high-speed electronic and optoelectronic devices.
摘要：
In a previous study, we have proposed a procedure to study global quantum discord in 1D chains whose ground states are described by matrix product states [Z.-Y. Sun et al., Ann. Phys. 359, 115 (2015)]. In this paper, we show that with a very simple generalization, the procedure can be used to investigate quantum mixed states described by matrix product density operators, such as quantum chains at finite temperatures and 1D subchains in high-dimensional lattices. As an example, we study the global discord in the ground state of a 2D transverse-field Ising lattice, and pay our attention to the scaling behavior of global discord in 1D sub-chains of the lattice. We find that, for any strength of the magnetic field, global discord always shows a linear scaling behavior as the increase of the length of the sub-chains. In addition, global discord and the so-called “discord density” can be used to indicate the quantum phase transition in the model. Furthermore, based upon our numerical results, we make some reliable predictions about the scaling of global discord defined on the n × n sub-squares in the lattice.
摘要：
Dual frequency comb generation has been the focus of many recent research efforts owing to its viability in a myriad of applications, ranging from precision measurement to high-speed optical communications. Here, with the state of the art of a single quantum dot (QD) coupled to a pillar microcavity [Nat. Nanotechnol. 12, 663 (2017)], we put forward an alternative setup for the generation of orthogonally polarized dual frequency combs and their corresponding control by using coherent two-tone cavity driving, i.e., a control laser and a probe laser. The present QD-pillar microcavity system operates in the weak-coupling regime, and this makes the experimental realization of the scheme easy. The underlying nonlinear process of the system, thanks to the QD-pillar interaction, for example, degenerate and nondegenerate four-wave mixing, results in efficient frequency comb formation. The dual combs consist of equidistant spectral lines whose spectral spacing coincides with the frequency difference between the control and probe lasers. So, programming this frequency difference between them enables us to tune both the comb-line spacing (i.e., repetition rate) and comb-line number in both vertical (V) and horizontal (H) polarizations. As compared with the previous approaches for dual microcomb generation, the present scheme has attractive features such as a tunable, slow repetition rate (as slow as a few megahertz), low input power (as low as a few nanowatts), and integrated compact nature in experimentally realistic operating regimes. The achievable low repetition rates are desirable to resolve narrower spectral lines and to enable use of low-power signal processing electronics. https://journals.aps.org/pra/abstract/10.1103/PhysRevA.98.023848
摘要：
One of the current challenges in second-harmonic generation (SHG) is to increase the efficiency of the second-harmonic conversion process while maintaining or even decreasing the fundamental-harmonic pump powers in a compact device. Here, we put forward an on-chip scheme to realize high-efficiency optical SHG in active-passive-coupled microring resonators with the aid of the intrinsic second-order nonlinearity. By careful analysis and extensive simulations, it is found that the introduction of an active microring resonator makes the strong SHG process feature an ultralow-power pump threshold, which is about four orders of magnitude lower than that in a single-microring resonator SHG system reported previously by X. Guo et al. [Optica 3, 1126 (2016)]. The observed SHG is enhanced by a factor of over 200 compared to the single-microring-resonator SHG system. The SHG conversion efficiency of over 72% can be reached with optical pump power as low as a few microwatts for our proposed device. This investigation may open a new route towards development of easily fabricated radiation sources of coherent high-energy (shorter-wavelength) photons with an ultralow-power laser-triggered SHG process.
摘要：
We present a perturbation technique to study the linear and nonlinear output characteristics of coherent photon transport in a parity-time ( PT)-symmetric double-microcavity system where one passive cavity contains a single quantum emitter. It is found that (i) for the linear transmission of a low-power input probe field, the output spectra of the proposed PT-symmetric system exhibit a single transparent resonance dip and two symmetric, strongly amplifying sidebands, i.e., an inverted dipole-induced transparency; and (ii) for the nonlinear transmission of the input probe field, giant optical third-order nonlinearities with high linear transmission rate and vanishing nonlinear absorption can be achieved efficiently when the system parameters are tuned properly so that a PT-symmetry phase transition occurs. The obtained results can be useful for quantum information processing, quantum nondemolition measurements of photons, and optical signal processing.
摘要：
A lot of experimental and theoretical studies of a system in cavity quantum electrodynamics (cavity QED), which consists of two spatially separated quantum emitters strongly coupled to a single optical cavity mode, have recently attracted much interest in the quantum optics community for various quantum information applications. Here, we propose a method for high-order harmonic generation in a photonic crystal microcavity coupled to single semiconductor quantum dots (QDs). The system is coherently driven by a bichromatic laser consisting of the control and signal fields at low input power (a few nanowatts) and the cavity output power via the cavity loss channel is monitored. Via numerical simulations, we thoroughly explore the difference of the generated high-order harmonic spectra between two QDs, one QD, and zero QDs in microcavity. The results clearly indicate that harmonic generation can be significantly enhanced via collective coherent coupling in the case of two spatially separated QDs coupled to the same photonic crystal microcavity mode. In addition, we present a study of the carrier-envelope phase (CEP) effect on high-order harmonic spectra, which may provide the insight of CEP effect in a new regime. Beyond this, our obtained results also apply to other classes of single-mode cavity-QED setup incorporating two-level atoms or comparable solid-state emitters.
摘要：
The formation of infrared solitons in graphene under Raman excitation is investigated using density-matrix approach. We find that the unique band structure and selection rules for the optical transitions near the Dirac point can result in extremely strong optical nonlinearity. Theoretical investigations with the aid of slowly varying envelope approximation and perturbation theory clearly indicate the existence of bright and dark solitons in Landau-quantized graphene. Actually, the formation of spatial soliton in such a material is the consequence of the balance between nonlinear effects and the dispersion properties. Also, the corresponding carrier frequency is tunable in the infrared range. These results can make us know better the crossover between optical solitons and graphene metamaterials. The predicted nonlinear optical effect in graphene may provide a new possibility for designing high-fidelity graphene-based information processing device.
摘要：
Based on a single atom coupled to a fiber-coupled, chip-based microresonator [B. Dayan et al., Science 319, 1062 (2008)], we put forward a scheme to generate optical frequency combs at driving laser powers as low as a few nanowatts. Using state-of-the-art experimental parameters, we investigate in detail the influences of different atomic positions and taper-resonator coupling regimes on optical-frequency-comb generation. In addition to numerical simulations demonstrating this effect, a physical explanation of the underlying mechanism is presented. We find that the combination of the atom and the resonator can induce a large third-order nonlinearity which is significantly stronger than Kerr nonlinearity in Kerr frequency combs. Such enhanced nonlinearity can be used to generate optical frequency combs if driven with two continuous-wave control and probe lasers and significantly reduce the threshold of nonlinear optical processes. The comb spacing can be well tuned by changing the frequency beating between the driving control and probe lasers. The proposed method is versatile and can be adopted to different types of resonators, such as microdisks, microspheres, microtoroids or microrings.
