In this paper, a diffraction-resistant arbitrary-trajectory plasmon with multitunability is introduced. The initial field of the plasmon is designed by us and superimposed with the composition of the Airy wave packet. Based on caustic phase modulation, arbitrary trajectories such as a parabola, hyperbola, and hyperbolic secant are achieved, by encoding the geometric functions into the wave front. The propagation trajectory can not only be accelerated by adjusting the geometric function parameters but also have its inclination angle adjusted. The migration of the energy center along the trajectory propagation direction is also found. The utilization of diffraction-resistant arbitrary trajectory plasmon also facilitates the control of plasmonic focus, enabling more on-chip manipulation possibilities. Also, we further illustrate the diffraction-resistant properties of the plasmon from the self-healing phenomenon. A scheme to generate the plasmon is proposed, and it is validated by the finite-difference time-domain numerical simulations.

Leveraging quantum effects in mechanical oscillators promises major advancements in nanometrology, including sensing and imaging. Microscopic cantilevers serve as versatile force sensors with broad applications in nanoscience, nanotechnology, and, increasingly, quantum sensing. We theoretically model and investigate the quantum mechanics of cantilever probes in atomic force microscopy under conditions of reduced thermal noise. Specifically, our model captures the cantilever interaction with a surface via long-range attractive van der Waals forces and short-range repulsive-adhesive interactions described by the Derjaguin-Muller-Toporov model. We find that when the probe resides within the attractive interaction regime, a coherent state emerges, whereas, in the repulsive regime, a squeezed state forms for the cantilever's deformation state. Our calculations explain the functional role of interaction potentials in the quantum dynamics of macroscopic mechanical systems, which are proving useful in quantum sensing and information processing. The presented calculations can be extended to investigate other interaction forces relevant to atomic force microscopy.

Here we discuss a phenomenon of sharp increase in the photon number noise at initial stages of propagation in tight-binding bosonic chains with off-diagonal disorder. Such a “noise avalanche” occurs under classical coherent excitation of waveguides and leads to high superthermal photon bunching. Additional classical excitation slows but cannot quench this noise avalanche. However, an additional single-photon excitation stops the avalanche.

Two-photon Hong-Ou-Mandel (HOM) interference is a pivotal quantum optical phenomenon, with broad applications in quantum information and metrology. Although conventional HOM interferometry loses sensitivity for transverse spatial separations beyond the photons' coherence length, we reveal experimentally that momentum-space measurements preserve this information through phase-sensitive two-photon interference fringes. Notably, we achieve micrometer-scale precision in determining transverse spatial separations an order of magnitude larger than the coherence length with only hundreds of photons. Our work establishes momentum-space interferometry as an important platform for quantum-enhanced metrology and information processing, overcoming the constraints of standard HOM techniques while providing new insights into quantum interference.

Achieving perfect control over the parameters defining a quantum gate is, in general, a very challenging task, and at the same time, environmental interactions can introduce disturbances to the initial states as well. Here we address the problem of how the imperfections in unitaries and noise present in the input states affect the entanglement-generating power of a given quantum gate—we refer to it as imperfect (noisy) entangling power. We observe that, when the parameters of a given unitary are chosen randomly from a Gaussian distribution centered around the desired mean, the quenched average entangling power—averaged across multiple random samplings—exhibits intriguing behavior like it may increase or show nonmonotonic behavior with the increase of disorder strength for certain classes of diagonal unitary operators. For arbitrary unitary operators, the quenched average power tends to stabilize, showing almost constant behavior with variation in the parameters instead of oscillating. Our observations also reveal that, in the presence of a local noise model, the input states that maximize the entangling power of a given unitary operator differ considerably from the noiseless scenario. Additionally, we report that the rankings among unitary operators according to their entangling power in the noiseless case change depending on the noise model and noise strength.

We propose an algorithm for directed graph centrality ranking, called the ancilla-assisted pseudo-Hermitian continuous-time quantum walk algorithm (AA-PHCTQW). AA-PHCTQW overcomes a common limitation for existing CTQW-based centrality ranking algorithms, both for undirected and directed graphs, which is the requirement of an initial state in a uniform superposition over all vertices. Leveraging an ancilla vertex, we enable the use of a single-vertex basis state as the initial system state, thereby significantly improving the algorithm's experimental feasibility and robustness against noise. We prove the correctness of AA-PHCTQW and analyze centrality measures from PHCTQW and AA-PHCTQW on random graphs. Furthermore, we experimentally validate the algorithm on a silicon-based reconfigurable photonic chip with heralded single-photon source and multiphoton sources, complete the AA-PHCTQW of three-node and nine-node directed graphs. Here we provide an on-chip experimental demonstration of a quantum walk algorithm for directed graph centrality ranking.

We propose a series of dissipation-assisted entanglement generation protocols that can be implemented on a trapped-ion quantum simulator. Our approach builds on the single-site molecular electron transfer (ET) model recently realized in experiment [So et al., Sci. Adv. 10, eads8011 (2024)]. This model leverages spin-dependent boson displacement and dissipation controlled by sympathetic cooling. We show that, when coupled to external degrees of freedom, the ET model can be used as a dissipative quantum control mechanism, enabling the precise tailoring of both spin and boson steady states of a target subsystem. We derive simplified analytical formalisms that offer intuitive insights into the dissipative dynamics. Using realistic interactions in a trapped-ion system, we develop a protocol for generating $N$-qubit and $N$-boson $W$ states. Additionally, we generalize this protocol to realize generic $N$-qubit Dicke states with tunable excitation numbers. Finally, we outline a realistic experimental setup to implement our schemes in the presence of noise sources.

Selective reflection is a high-resolution spectroscopic method that allows the probing of atomic and molecular gases in the near field of dielectric cell windows. It is a sensitive technique for measuring interactions between excited atoms and surfaces, thus providing a unique tool to probe resonant effects in Casimir-Polder physics. The theoretical modeling of selective reflection spectra has thus far employed the infinite Doppler approximation which assumes that the Doppler shift dominates over the atom-surface interactions as well as the homogeneous transition linewidth. Here we extend the theoretical treatment of selective reflection spectra to include the effects of finite Doppler width. This allows us to analyze the regime of very large Casimir-Polder interactions, relevant for Rydberg atom spectroscopy, and revisit previous analyses of experiments with low-lying excited states. Further, this will aid in determining the signatures of quantum friction in vapor cell spectroscopy.

We perform a complete calculation of $\alpha {\left(Z\alpha \right)}^{5}m$ radiative corrections to the finite nuclear size, the recoil finite size, and the nuclear polarizability effects in atomic systems. Results confirm very good agreement for the mean square charge radii difference $r_d^2-r_p^2$ between the deuteron and the proton, as measured in electronic and muonic isotope shifts.

We present a method for determining the atom number distribution of few atoms in a tight optical tweezer from their fluorescence distributions. In the tight tweezer regime, the detection light causes rapid atom loss due to light-assisted collisions. This in turn leads to non-Poissonian and overlapping fluorescence distributions for different initial atom numbers, and commonly used threshold techniques fail. We use maximum likelihood estimation algorithms to fit model distributions that account for the atom loss. This gives accurate atom number distributions for relatively few experimental runs (about 600 is sufficient) to sample a photon number distribution. We show that the method can be extended to situations when the photon number distributions for known initial atom numbers cannot be modeled, at the cost of requiring a higher number of experimental runs.

Optical nonreciprocity, violating Lorentz reciprocity, is pivotal for advanced classical optics and quantum networks. Despite significant progress in its realization across diverse systems, intricate interconnection and transition between reciprocity and nonreciprocity remain elusive, which poses a limitation on the development of controllable nonreciprocal devices. Here, we demonstrate that inherent atomic dissipation, traditionally detrimental, serves as a flexible tool for nonreciprocity control. It is shown that the dissipation-dependent atomic population and coherence effects exhibit competitive yet distinct characteristics in breaking Lorentz reciprocity, enabling the coexistence and interconversion of reciprocal and nonreciprocal states within a V-type atomic system. By implementing a dissipation-engineered switching framework, a nontrivial transition between reciprocity and nonreciprocity is achieved. These findings establish the direct link between microscopic dissipation and dynamic nonreciprocity control, paving a way for all-optical reconfigurable nonreciprocity.

Ionization of a target gas by a strong laser field, which is the first step for many processes studied in strong-field physics, results in the appearance of free electrons. Recently, we showed that the interaction of the laser field with these electrons affects the quantum state of the field, leading to the formation of nonclassical and non-Gaussian field states [Phys. Rev. A 110, 023115 (2024)]. In this paper we generalize our model to the multimode case, which allows us to consider Thomson scattering (TS) of the laser field by the electrons. We show that for sufficiently long pulses under typical experimental conditions TS causes coherent transfer of photons from the strong laser mode to weak modes with close frequencies and wave vectors. This results in a displacement of the initial coherent state of the laser field similar to that recently discovered and caused by the high-order harmonic generation (HHG) process [M. Lewenstein et al., Nat. Phys. 17, 1104 (2021)]. The similarity with HHG suggests that, by conditioning on TS, multiphoton Schrödinger cat states of the laser field can be generated. The TS mechanism has a different dependence on the pulse parameters compared with the HHG mechanism, which may facilitate more efficient and robust generation of cat states. In particular, it also works for circularly polarized fields, in which case HHG does not occur.

We show that quantum rotational wavepacket dynamics in molecules can be rigorously described by a system-environment model, which consists of a rotational subsystem coupled to a magnetically tunable spin bath formed by the nuclear spins within the molecule. The central rotor model shares similarities with the paradigmatic central spin model but features much richer rotational dynamics that is sensitive to the molecule's environment, which can be initiated and probed with short laser pulses used to control molecular orientation and alignment. We present numerical simulations of the nuclear-spin-bath-induced rotational decoherence dynamics of KRb molecules, which exhibit remarkable sensitivity to an external magnetic field. Our results show that ultracold molecular gases provide a natural platform for the experimental realization of the CRM.

We reveal a quantum coherent state characterized by composite bosonic trions, wherein paired fermions further bind with bosons, in one-dimensional Bose-Fermi mixtures. This phase emerges in two separate models, both featuring onsite boson-fermion attraction that induces negative binding energy for the composite trions. The first is the pair-hopping model, in which spinless fermions undergo pair hopping to form preformed pairs. The second is the extended Bose-Fermi-Hubbard model, describing dipolar bosons and fermions with density-density interactions. Notably, the formation of composite trions is independent of the specific pairing interactions of fermions. Extensive density-matrix renormalization-group calculations demonstrate the quasicondensation of the composite trions, evidenced by algebraically decaying correlations of trions, gapped single-particle excitations, and suppressed fermion pair correlations. Our findings provide valuable insights into the three-body pairing mechanism in mixed-particle systems.

Photon avalanche (PA) is a nonlinear process that presents a large growth of the upconversion fluorescence intensity signal and a strong absorption of the excitation light source occurring in lanthanide-doped systems. Conventional excitation schemes may introduce unwanted detrimental effects such as linear transmission losses and thermal effects. Here, a model is proposed in which the triggering mechanism for the PA effect is the absorption of a single photon by a pair of neighboring ions. The proposed model was studied using a rate equation system that describes the population dynamics of the electronic states of praseodymium ions in a silica fiber. The theoretical simulations confirm the presence of transmission attenuation and PA upconversion fluorescence when the lanthanide ions are at a short distance (a few angstroms), which guarantees the necessary PA positive feedback condition: a large cross-relaxation energy transfer rate among the lanthanide ions.

As the flow of time governs all evolutions, the reversal of time evolution has garnered intense research in many fields. The phenomenon of Landau-Zener (LZ) tunneling is one of the most remarkable time evolution processes in quantum mechanics. In this work, we study LZ tunneling with time-reversal operation in a Floquet system of synthetic temporal lattices, which is formed by the evolution of optical pulses in coupled fiber loops. With an abrupt change of gauge potential and the splitting parameter imposed on the lattices, the two eigenstates of the system are exchanged so that the time-reversal operation is realized. In the experiment, we demonstrate that time-reversal operations eliminate path degeneracy through propagation path reconstruction. The measurement of the dynamics of LZ tunneling and that with time-reversal operation is shown by applying the quenching dynamics. The study provides an effective approach to perform the LZ tunneling with time-reversal operation and expands our capability of measuring various tunneling processes. These methods can also be applied to optical interferometers, fiber communications, and quantum control.

Propagating modes of light with Wigner distributions exhibiting negativity are of fundamental interest in quantum optics and represent a key resource in the pursuit of optics-based quantum information technologies. Most schemes proposed or implemented for the generation of such modes are probabilistic in nature and rely on heralding by detection of a photon or on conditional methods where photons are separated from the original field mode by a beam splitter. We demonstrate theoretically, using a cascaded-quantum-system model, the possibility of deterministic generation of Wigner negativity in temporal modes of the steady-state emission of a two-level system driven by finite-bandwidth quadrature-squeezed light. Optimal negativity is obtained for a squeezing bandwidth similar to the linewidth of the transition of the two-level system. While the Wigner distribution associated with the incident squeezed light is Gaussian and everywhere positive, the Wigner functions of the outgoing temporal modes show distinct similarities and overlap with a superposition of displaced squeezed states.