-Li Cui

Coherent perfect absorption, transmission, and synthesis in a double-cavity optomechanical system

We study a double-cavity optomechanical system in which a movable mirror with perfect reflection is inserted between two fixed mirrors with partial transmission. This optomechanical system is driven from both fixed end mirrors in a symmetric scheme by two strong coupling fields and two weak probe fields. We find that three interesting phenomena: coherent perfect absorption (CPA), coherent perfect transmission (CPT), and coherent perfect synthesis (CPS) can be attained within different parameter regimes. That is, we can make two input probe fields totally absorbed by the movable mirror without yielding any energy output from either end mirror (CPA); make an input probe field transmitted from one end mirror to the other end mirror without suffering any energy loss in the two cavities (CPT); make two input probe fields synthesized into one output probe field after undergoing either a perfect transmission or a perfect reflection (CPS). These interesting phenomena originate from the efficient hybrid coupling of optical and mechanical modes and may be all-optically controlled to realize novel photonic devices in quantum information networks.

Dynamically induced double photonic bandgaps in the presence of spontaneously generated coherence

We study a four-level double-Lambda system with spontaneously generated coherence driven by a standing-wave coupling field. It is found that two well-developed photonic bandgaps with reflectivities of about 90% can be generated on the probe resonance in the presence of maximal spontaneously generated coherence. The induced double photonic bandgaps become, however, severely malformed when spontaneously generated coherence vanishes. Dynamic control of the double photonic bandgaps may be exploited to achieve a novel two-port double-channel routing scheme for weak light signals in quantum networks.

Highly efficient four-wave mixing induced by quantum constructive interference in rubidium vapour

We demonstrate efficient four-wave mixing with an intensity conversion efficiency of nearly 100% in theory without considering the Doppler-broadening effect in a four-level double-Λ system of hot 87Rb gas. The corresponding experimental value of about 73% was reported in our earlier work under the same conditions. This dramatic efficiency is critically dependent on the constructive interference between two four-wave mixing processes relevant to the internally generated four-wave mixing signal.

Double photonic bandgaps dynamically induced in a tripod system of cold atoms

A tripod atomic system driven by two standing-wave fields (a coupling and a driving) is explored to generate tunable double photonic bandgaps in the regime of electromagnetically induced transparency. Both photonic bandgaps depend critically on frequency detunings, spatial periodicities, and initial phases of the two standing-wave fields. When the coupling and driving detunings are very close, a small fluctuation of one standing-wave field may demolish both photonic bandgaps. If the two detunings are greatly different, however, each standing-wave field determines only one photonic bandgap in a less sensitive way. Dynamic generation and elimination of a pair of photonic bandgaps shown here may be exploited toward the end of simultaneous manipulation of two weak light signals even at the single-photon level.

Coherent generation and efficient manipulation of dual-channel robust stationary light pulses in ultracold atoms

We study the dynamic processes of reversible dual-channel light memory in a double-tripod atomic system by modulating only a pair of counterpropagating control fields in time. We find that two pairs of stationary light pulses (SLPs) can be simultaneously generated when we switch on both control fields after storage. Two incident signal fields in two channels can be released either simultaneously from the same surface of the sample, or at different times from the same or different surfaces of the sample, depending on the time modulation of the two control fields, the time sequence of the input signal fields, and the group velocities of the signal fields propagating in medium, which could be successfully manipulated in each channel. Comparing with the light storage in spin-wave excitations, the SLPs may suffer a little space-dependent diffusion but maintain optical components required for nonlinear optical interactions. These results could be used to study the enhanced low-noises nonlinear interaction between dual-channel SLPs, which can maximize the interaction time. Besides, this scheme could also be explored to design synchronous multitasking information processing during light memory processes at low-light even below single-photon level.

Dynamic generation of robust and controlled beating signals in an asymmetric procedure of light storage and retrieval

We propose an efficient scheme for the robust and controlled generation of beating signals in a sample of stationary atoms driven into the tripod configuration. This scheme relies on an asymmetric procedure of light storage and retrieval where the two classical coupling fields have equal detunings in the storage stage but opposite detunings in the retrieval stage. A quantum probe field, incident upon such an atomic sample, is first transformed into two spin coherence wave-packets and then retrieved with two optical components characterized by different time-dependent phases. Therefore the retrieved quantum probe field exhibits a series of maxima and minima (beating signals) in intensity due to the alternative constructive and destructive interference. This interesting phenomenon involves in fact the coherent manipulation of two dark-state polaritons and may be explored to achieve the fast quantum limited measurement.

Marking slow light signals with fast optical precursors in the regime of electromagnetically induced transparency

In order to identify special information from a light pulse sequence, we propose a few viable schemes for marking a desired slow light signal with a fast optical precursor in a Λ-type and N-type atomic system. The fast optical precursor is characterized by transient beating patterns originating from the temporal discontinuity of the marking pulse at the sharp rising or falling edge. Compared with the schemes in the Λ system, the one in the N system has the advantage of flexibility in situations in which we are not the sender of the original probe signals. Besides, there is no disturbance to the probe signals nor an undesired main pulse coming from the marking field.

Steady optical spectra and light propagation dynamics in cold atomic samples with homogeneous or inhomogeneous densities

We study both steady and dynamic optical responses of three samples with the same amounts of cold atoms but very different density functions. These samples are driven into the regime of electromagnetically induced transparency by a probe and a coupling in the Lambda configuration. When the coupling is in the traveling-wave pattern, all samples have the same transmission spectra and therefore identical transmitted pulses at the sample exits. In the case of a standing-wave coupling, however, very different reflection and transmission spectra are found for the three samples. Accordingly, reflected pulses at the sample entrances and transmitted pulses at the sample exits are quite sensitive to the spatial inhomogeneity of cold atoms. These interesting phenomena are qualitatively analyzed in terms of constructive and destructive interference between forward and backward probe photons scattered by a standing-wave atomic grating.

Resonant gain suppression and quantum destructive interference in a three-level open V system

We investigate the steady optical properties of a three-level open V system (i.e. a four-level closed atomic system) through both analytical and numerical calculations. Our results show that the resonant probe gain can be greatly suppressed to generate a narrow and deep transparency window associated with very steep abnormal dispersion. The underlying physics is identified as the perfect quantum destructive interference between a pair of dressed state transition pathways, which is usually believed to be absent in three-level closed V systems. In addition, we show that the transparency window and its associated abnormal dispersion can be used to realize a striking propagation dynamics where a light pulse may have a negative group velocity of small absolute values and experience little gain or absorption.

The influence of spontaneously generated coherence on atom-photon entanglement in a Λ-type system with an incoherent pump

Owing to interference induced by spontaneous emission, the density-matrix equations in a three-level Λ-type system have an additional coherence term, which plays a critical role in modulating the inversionless gain and electromagnetically induced transparency effect. In addition, it is shown that spontaneously generated coherence (SGC) has an effect on the entanglement between an atom and a photon of the coupling laser field by calculating the degree of entanglement (DEM) of the atomic system. In this paper, we investigate the influence of the SGC effect on atom-photon entanglement in a Λ-type system, which generally remains a high entangled state. When an incoherent pump source is introduced, we find that the SGC effect could exert considerable influence on the atom reduced entropy under certain conditions for both transient and steady states. More interestingly, such an incoherent pump field could actively affect the short-time dynamic behaviors of the transient quantum entangled state at a certain range of pump rate as a typical coherent case.