Session LL03: V: Progress in AMO Physics I

Towards a Realistic Model for Cavity-Enhanced Atomic Frequency Comb Quantum Memories: The Critical Role of Dispersion

Future quantum networks rely on long-distance quantum communication which is limited due to the unavoidable photon transmission loss in optical fibers. Quantum repeaters (QRs) are promising quantum alternatives to play the role of classical amplifiers. Atomic frequency comb (AFC) quantum memory implemented in rare-earth-ion doped crystals is a favorable protocol in long-distance quantum communication based on quantum repeaters. Putting the AFC inside an asymmetric optical cavity enhances the storage efficiency but makes the measurement of the comb properties challenging. We develop a theoretical model for cavity-enhanced AFC quantum memory and investigate the role of dispersion in the model. We demonstrate that including the effect of dispersion leads to a good agreement between experimental and model results, whereas the model without dispersion falls short strikingly. Most importantly, the model with dispersion provides a much closer quantitative agreement for estimating the efficiency and a drastically better description of how the efficiency changes as a function of detuning. Furthermore, it better captures certain qualitative features of the experimental reflectivity. Our model is a step forward to accurately estimating the created comb properties, such as the optical depth inside the cavity, and so to being able to make precise predictions of the performance of the prepared cavity-enhanced AFC quantum memory.   

Superentanglement: Unification of Quantum and Classical Physics

We postulated based on widely accepted principles, reinterpreted mathematical equations, and worked from a bottom-up approach, rather than a top-down approach in an attempt to gain a greater understanding of various universal phenomenon. Accordingly, in order to solve for the anomalies presented by quantum physics, we applied these reinterpreted postulates to collapse of the wave function and quantum entanglement using models based on Euclidian geometry. We further applied this premise and determined entanglement leads to gravity, time, mass, velocity, particle spin, as well as the subatomic and atomic structure, confirming our hypothesis the universe is simultaneously local and non-local.   

Carbon dioxide (CO2) as a quantum molecular sensor in protoplanetary disks.State-to-state rovibrational transition rates for CO2 in the bend mode in collisions with helium (He) atoms.

Modeling environments that are not in local thermal equilibrium, such as protoplanetary disks or planetary atmospheres, with molecular spectroscopic data requires knowledge of the rates of rovibrationally inelastic molecular collisions. Here, we present rate coefficients for temperatures up to 500 K for CO₂-He collisions in which CO₂ is (de)excited in the bend mode. They are obtained from numerically exact coupled-channel (CC) calculations as well as from calculations with the less demanding coupled-states approximation (CSA) and the vibrational close-coupling rotational infinite-order sudden (VCC-IOS) method. All of the calculations are based on a new accurate ab initio four-dimensional CO₂-He potential surface including the CO₂ bend mode. We find that the rovibrationally inelastic collision cross sections and rate coefficients from the CSA and VCC-IOS calculations agree mostly to within 50% with the CC results at the rotational state-to-state level and to within 20% for the overall vibrational quenching rates except for temperatures below 50 K where resonances provide a substantial contribution. Our CC quenching rates agree with the most recent experimental data within the error bars. We also compared our results with data from Clary et al. calculated in the 1980's with the CSA and VCC-IOS methods and a simple atom-atom model potential based on ab initio Hartree-Fock calculations and found that their cross sections agree fairly well with ours for collision energies above 500 cm^-1, but that the inclusion of long range attractive dispersion interactions is crucial to obtain reliable cross sections at lower energies and rate coefficients at lower temperatures.   

Cooperative non-Markovian emission in a single-band waveguide

We investigate the collective radiative dynamics of two quantum emitters emitting two bosons in a 1D single-band waveguide. While this problem is normally solved approximately, with the Markovian approximation being the most extended, we solve the system exactly and analytically. This opens up the possibility of exploring, without relying on numerical methods, different topics such as the connection between superradiance and synchronization, the formation of multiemitter-multiexcitation bound states (states akin to a molecule of light), or decay-induced entanglement.   

A Diffusion Quantum Monte Carlo Approach to the Polaritonic Ground State

Constucting and using polaritonic states (i.e., hybrid electron-photon states) for chemical applications have recently become one of the most prominent and active fields that connects the communities of chemistry and quantum optics. Modeling of such polaritonic phenomena using ab initio approaches calls for new methodologies, leading to the reinvention of many commonly used electronic structure methods, such as Hartree-Fock, density functional, and coupled cluster theories. In this work, we explore the formally exact diffusion quantum Monte Carlo approach (DQMC) to obtain numerical solutions to the polaritonic ground state during the dissociation of the H₂ molecular system. We examine various electron-nuclear-photon properties throughout the dissociation, such as changes to the minimum of the cavity Born-Oppenheimer surface, the localization of the electronic wavefunction, and the average mode occupation. Finally, we  directly compare our results to that obtained with state-of-the-art, yet approximate, polaritonic coupled cluster approaches.   

Sub-nanometer confinement and phononic bus in multi-dimensional atomic lattice

Optical lattices are the basic blocks of atomic quantum technology. The scale and resolution of these lattices are diffraction-limited to the light wavelength. Tight confinement of single sites in conventional lattices requires excessive laser intensity which in turn suppresses the coherence due to enhanced scattering. This talk proposes a new scheme for atomic optical lattice with sub-wavelength spatial structure. The atom light interaction coupling combined with Rydberg interaction has opened a wide range of applications in quantum technology [1-10]. This presentation utilises the nonlinear optical response of the three-level Rydberg-dressed atoms to form ultra-narrow trapping potentials [11]. This arrangement is not constrained by the diffraction limit of the driving fields. The lattice consists of a 3D array of ultra-narrow Lorentzian wells with sub-nanometer widths. These extreme scales are now optically accessible by a hybrid scheme deploying the dipolar interaction and optical twist of atomic eigenstates. The interaction-induced two-body resonance that forms the trapping potential [12], only occurs at a peculiar laser intensity, localizing the trap sites to ultra-narrow regions over the standing-wave drivin. The tight confinement is desired for quantum logic operations with Rydberg-Fermi interaction [13-14], and distance selective operations [15]. Finally, the interaction induced trapping forms collective motional modes among lattice sites generating phononic bus in three dimensional lattice.

References:

Optimal population transfer in driven-dissipative systems using adiabatic rapid passage

Adiabatic rapid passage (ARP) is extensively used to achieve efficient transfer of population between two levels of atomic systems. Landau and Zener accurately derived the transfer probability of ARP for closed systems following unitary dynamics and showed that this probability increases with higher drive amplitude. In this work, we adopt a quantum master equation approach to investigate the dissipative effects of the applied drive on the performance of ARP that is implemented using a linearly-chirped pulse on a two-level system interacting with its environment. From the Landau-Zener formula, the population transfer was known to be enhanced with increasing drive amplitude. However, we show that beyond a threshold value of the drive amplitude, the transfer probability is reduced because of the detrimental effect of the drive-induced dissipation. We report that the interplay between the two processes results in an optimal population transfer. Furthermore, we propose a phenomenological model that qualitatively explains the observed nonmonotonic behavior of the transfer. Using this model, we also estimate the optimum time at which the maximum population transfer occurs. We perform the analysis for rectangular as well as Gaussian pulse profiles and conclude that the use of a Gaussian pulse leads to more efficient transfer.   

Improved selection of dark states in the presence of drive-induced dissipation.

We revisit the coherent population trapping (CPT) of a three-state system in the

presence of environmental fluctuations and strong electromagnetic driving fields. To this end, we

use a fluctuation-regulated quantum master equation that takes into account the drive-induced

dissipation (DID) in the system. DID originates from the combined effect of a driving field and

environmental fluctuations. We report that increasing DID shows a narrowing of CPT linewidth

and hence improved selection of the dark states. As such, the DID enhances the sensitivity of

CPT at a driving strength much larger than the system’s relaxation rates. We also discuss the

practical implementation of the scheme along with possible applications.   

Squeezing in atomic boson sampling

Recently, atomic boson sampling of excited atom occupations in an equilibrium interacting gas with a

Bose-Einstein condensate (BEC) has been suggested [V.V. Kocharovsky et al., PRA 106, 063312 (2022),

Entropy 24, 1771 (2022)] as a process that could be ♯P-hard for classical computing. Here we consider

this process within the simplest possible model of a BEC trap – the box with the periodic boundary

conditions. Remarkably, this model remains pertained to ♯P-hardness and quantum supremacy. We

calculate, analytically and numerically, the effect of single- and two-mode squeezing on the statistics of

sampling from a single eigen-squeeze mode and two counter-propagating waves. Although not complex

enough on its own to show ♯P-hard behavior, single- or two-mode sampling reveals the basic

mechanism for the emergence of the computational ♯P-hardness in a many-body quantum system of

interacting atoms.   

Optically levitated single droplet study of the sea spray aerosol that contains the mercuric halides

Mercury exists in the atmosphere in three major forms: gaseous elemental mercury, gaseous oxidized mercury, and particulate-bound mercury. Among these three forms, the gaseous-phase mercury takes up more than 90% and has been well studied. However, the particulate-bound mercury that is mainly related to the heterogeneous surface, such as aerosols, air-water interfaces, etc., has been less investigated. This is mainly due to the complex nature of heterogeneous chemistry and the experimental difficulties in making accurate measurements.

Optical trapping was demonstrated that can be used to simulate the real atmospheric environment of a single aerosol particle in air. In this study, we used optical trapping-Raman spectroscopy to study the single droplet of the sea spray aerosol that contains Hg(II) halides (HgX₂, X=Cl, Br).  The single droplets were trapped in air under different conditions (exposure to ozone or UV radiation) with different relative humidities (RH). The results were analyzed by the single particle-Raman spectra. We discussed the results in (1) The equilibrium process and hygroscopic properties of the sea spray aerosol; (2) The chemical reaction that happens between ozone and Hg(II) halides in sea spray aerosol in the single particle level; (3) The influence of the UV radiation on the Hg(II) halides in sea spray aerosol.