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Luqi Yuan

Publications and source records attributed to Luqi Yuan.

62 records · Page 4Linked to original sources
arXiv2016

Synthetic gauge potential and effective magnetic field in a Raman medium undergoing molecular modulation

We theoretically demonstrate non-trivial topological effects for a probe field in a Raman medium undergoing molecular modulation processes. The medium is driven by two non-collinear pump beams. We show that the angle between the pumps is related to an effective gauge potential and an effective magnetic field for the probe field in the synthetic space consisting of a synthetic frequency dimension and a spatial dimension. As a result of such effective magnetic field, the probe field can exhibit topologically-protected one-way edge state in the synthetic space, as well as Landau levels which manifests as suppression of both diffraction and sideband generation. Our work identifies a previously unexplored route towards creating topological photonics effects, and highlights an important connection between topological photonics and nonlinear optics.

physics.optics↗
arXiv2015

Photonic gauge potential in a system with a synthetic frequency dimension

We generalize the concept of photonic gauge potential in real space, by introducing an additional "synthetic" frequency dimension in addition to the real space dimensions. As an illustration we consider a one-dimensional array of ring resonators, each supporting a set of resonant modes having a frequency comb with spacing $Ω$, undergoing a refractive index modulation at the modulation frequency equal to $Ω$. We show that the modulation phase provides a gauge potential in the synthetic two-dimensional space with the dimensions being the frequency and the spatial axes. Such gauge potential can create a topologically protected one-way edge state in the synthetic space that is useful for high-efficiency generation of higher-order side bands.

physics.optics↗
arXiv2015

Topological phase transitions in superradiance lattices

Topological phases of matters are of fundamental interest and have promising applications. Fascinating topological properties of light have been unveiled in classical optical materials. However, the manifestation of topological physics in quantum optics has not been discovered. Here we study the topological phases in a two-dimensional momentum-space superradiance lattice composed of timed Dicke states (TDS) in electromagnetically induced transparency (EIT). By periodically modulating the three EIT coupling fields, we can create a Haldane model with in-situ tunable topological properties, which manifest themselves in the contrast between diffraction signals emitted by superradiant TDS. The topological superradiance lattices provide a controllable platform for simulating exotic phenomena in condensed matter physics and offer a basis of topological quantum optics and novel photonic devices.

physics.optics↗
arXiv2015

Topologically non-trivial Floquet band structure in a system undergoing photonic transitions in the ultra-strong coupling regime

We consider a system of dynamically-modulated photonic resonator lattice undergoing photonic transition, and show that in the ultra-strong coupling regime such a lattice can exhibit non-trivial topological properties, including topologically non-trivial band gaps, and the associated topologically-robust one-way edge states. Compared with the same system operating in the regime where the rotating wave approximation is valid, operating the system in the ultra-strong coupling regime results in one-way edge modes that has a larger bandwidth, and is less susceptible to loss. Also, in the ultra-strong coupling regime, the system undergoes a topological insulator-to-metal phase transition as one varies the modulation strength. This phase transition has no counter part in systems satisfying the rotating wave approximation, and its nature is directly related to the non-trivial topology of the quasi-energy space.

physics.optics↗
arXiv2015

Dynamic localization of light from a time-dependent effective gauge field for photons

We introduce a method to achieve three-dimensional dynamic localization of light. We consider a dynamically-modulated resonator lattice that has been previously shown to exhibit an effective gauge potential for photons. When such an effective gauge potential varies sinusoidally in time, dynamic localization of light can be achieved. Moreover, while previous works on such effective gauge potential for photons were carried out in the regime where the rotating wave approximation is valid, the effect of dynamic localization persists even when the counter-rotating term is taken into count.

physics.optics↗
arXiv2014

Sideband generation of transient lasing without population inversion

We suggest a method to generate coherent short pulses by generating a frequency comb using lasing without inversion in the transient regime. We use a universal method to study the propagation of a pulse in various spectral regions through an active medium that is strongly driven on a low-frequency transition on a time scale shorter than the decoherence time. The results show gain on the sidebands at different modes can be produced even if there is no initial population inversion prepared. Besides the production of ultra-short pulse this frequency comb may have applications towards making short-wavelength or Tera-hertz lasers.

physics.optics↗
arXiv2011

Quantum correlations and violation of Bell inequality induced by External Field in a two photon radiative cascade

We study the polarization dependent second order correlation of a pair of photons emitted in a four level radiative cascade driven by an external field. It is found that the quantum correlations of the emitted photons, degraded by the energy splitting of the intermediate levels in the radiative cascade can be efficiently revived by a far detuned external field. The physics of this revival is linked to an induced stark shift and the formation of dressed states in the system by the non-resonant external field. Further, we investigated the competition between the effect of the coherent external field and incoherent dephasing of the intermediate levels. We found that the degradation of quantum correlations due to the incoherent dephasing can be content for small dephasing with the external field. We also studied the non-locality of the correlations by evaluating the Bell's inequality in the linear polarization basis for the radiative cascade. We find that the Bell parameter decreases rapidly with increase in the intermediate level energy splitting or incoherent dephasing rate to the extent that there is no violation. However, the presence of an external field leads to control over the degrading mechanisms and preservation of nonlocal correlation among the photons. This in turn can induce, violation of Bell's inequality in the radiative cascade for arbitrary intermediate level splitting and small incoherent dephasing.

quant-ph↗