Biphoton focusing for two-photon excitation

Exact time-reversal focusing of acoustic and quantum excitations in open cavities: The perfect inverse filter

The time-reversal mirror (TRM) prescribes the reverse playback of a signal to focalize an acoustic excitation as a Loschmidt echo. In the quantum domain, the perfect inverse filter (PIF) processes this signal to ensure an exact reversion provided that the excitation originated outside the cavity delimited by the transducers. We show that PIF takes a simple form when the initial excitation is created inside this cavity. This also applies to the acoustical case, where it corrects the TRM and improves the design of an acoustic bazooka. We solve an open chaotic cavity modeling a quantum bazooka an…

Collective excitations using a room-temperature gas of 3-level atoms in a cavity

We theoretically investigate an ensemble of three-level room-temperature atoms in a two-mode optical cavity, focusing on the case of counterpropagating light fields. We find that in the limit of large detunings the problem admits relatively simple and intuitive solutions. When a classical field drives one of the transitions, the system becomes equivalent to an ensemble of two-level atoms with suppressed Doppler broadening. In contrast, when the same transition is driven with a single photon, the system collectively behaves like a single two-level atom. This latter result is particularly releva…

III-V族半导体微环中通过下转换产生光子对：模态色散与准相位匹配

Photon pair generation via down-conversion in III-V semiconductor microrings: modal dispersion and quasi-phase matching

本文研究III-V族半导体微环谐振器利用准相位匹配和模态色散实现高效自发参量下转换，给出双光子波函数解析表达式并表征压缩态，证明简单微环结构即可实现高转换效率，有望实现非高斯态的确定性生成。

Feynman Diagrams for Dispersion Interactions Out of Equilibrium -- Two-Body Potentials for Atoms with Initial Excitation

Diagrammatic techniques are well-known in the calculation of dispersion interactions between atoms or molecules. The multipolar coupling scheme combined with Feynman ordered diagrams significantly reduces the number of graphs compared to elementary stationary perturbation theory. We review calculations of van der Waals-Casimir-Polder forces, focusing on two atoms or molecules one of which is excited. In this case, calculations of the corresponding force are notorious for mathematical issues connected to the spontaneous decay of the excitation. Treating such unstable states in a full non-equili…

Efficient coupling of photons to a single molecule and the observation of its resonance fluorescence

Single dye molecules at cryogenic temperatures display many spectroscopic phenomena known from free atoms and are thus promising candidates for fundamental quantum optical studies. However, the existing techniques for the detection of single molecules have either sacrificed the information on the coherence of the excited state or have been inefficient. Here we show that these problems can be addressed by focusing the excitation light near to the absorption cross section of a molecule. Our detection scheme allows us to explore resonance fluorescence over 9 orders of magnitude of excitation inte…

单层WSe₂中基于本征态的选择纠缠双光子吸收

Eigenstate-Selective Entangled Two-Photon Absorption in Monolayer WSe$_2$

研究揭示了极化纠缠光子对的贝尔态相位调控单层WSe₂中双激发本征态分布的机制，通过谷度和相位控制实现不同本征态的选择性激发。

Light-Shift Imbalance Induced Blockade of Collective Excitations Beyond the Lowest Order

Current proposals focusing on neutral atoms for quantum computing are mostly based on using single atoms as quantum bits (qubits), while using cavity induced coupling or dipole-dipole interaction for two-qubit operations. An alternative approach is to use atomic ensembles as qubits. However, when an atomic ensemble is excited, by a laser beam matched to a two-level transition (or a Raman transition) for example, it leads to a cascade of many states as more and more photons are absorbed^1. In order to make use of an ensemble as a qubit, it is necessary to disrupt this cascade, and restrict the …

Excitation of a single atom with exponentially rising light pulses

We investigate the interaction between a single atom and optical pulses in a coherent state with a controlled temporal envelope. In a comparison between a rising exponential and a square envelope, we show that the rising exponential envelope leads to a higher excitation probability for fixed low average photon numbers, in accordance to a time-reversed Weisskopf-Wigner model. We characterize the atomic transition dynamics for a wide range of the average photon numbers, and are able to saturate the optical transition of a single atom with ~50 photons in a pulse by a strong focusing technique. Fo…

Long-lived entanglement of two multilevel atoms in a waveguide

We study the presence of nontrivial bound states of two multilevel quantum emitters and the photons propagating in a linear waveguide. We characterize the conditions for the existence of such states and determine their general properties, focusing in particular on the entanglement between the two emitters, that increases with the number of excitations. We discuss the relevance of the results for entanglement preservation and generation by spontaneous relaxation processes.

Anderson Localization of Composite Excitations in Disordered Optomechanical Arrays

Optomechanical arrays are a promising future platform for studies of transport, many-body dynamics, quantum control and topological effects in systems of coupled photon and phonon modes. We introduce disordered optomechanical arrays, focusing on features of Anderson localization of hybrid photon-phonon excitations. It turns out that these represent a unique disordered system, where basic parameters can be easily controlled by varying the frequency and the amplitude of an external laser field. We show that the two-species setting leads to a non-trivial frequency dependence of the localization l…

Entropy Dynamics of Phonon Quantum States Generated by Optical Excitation of a Two-Level System

In quantum physics, two prototypical model systems stand out due to their wide range of applications. These are the two-level system (TLS) and the harmonic oscillator. The former is often an ideal model for confined charge or spin systems and the latter for lattice vibrations, i.e., phonons. Here, we couple these two systems, which leads to numerous fascinating physical phenomena. Practically, we consider different optical excitations and decay scenarios of a TLS, focusing on the generated dynamics of a single phonon mode that couples to the TLS. Special emphasis is placed on the entropy of th…

双Lévy指数分数Kerr介质中孤子坍缩、调制不稳定性与怪波激发的抑制

Suppression of soliton collapses, modulational instability, and rogue-wave excitation in two-Lévy-index fractional Kerr media

本文研究双Lévy指数分数Kerr介质中的一维分数非线性薛定谔方程，发现双指数系统可抑制单指数系统中的孤子坍缩，并分析了孤子稳定性、调制不稳定性及一阶和二阶怪波的激发。