A generalized effective spin-chain model is developed for studies of strongly interacting spinor gases in a one-dimensional (1D) optical lattice. The spinor gas is mapped to a system of spinless fermions and a spin chain. A generalized effective spin-chain Hamiltonian that acts on the mapped system is developed to study the static and dynamic properties of the spinor gas. This provides a computationally efficient alternative tool to study strongly interacting spinor gases in 1D lattice systems. This formalism permits the study of spinor gases with arbitrary spin and statistics, providing a generalized approach for 1D strongly interacting gases. By virtue of its simplicity, it provides an easier tool to study and gain deeper insights into the system. In combination with the model defined previously for continuum systems, a unified framework is developed. Studying the mapped system using this formalism recreates the physics of spinor gas in 1D lattice. Additionally, the time evolution of a quenched system is studied. The generalized effective spin-chain formalism has potential applications in the study of a multitude of interesting phenomena arising in lattice systems such as high-$T_c$ superconductivity and the spin-coherent and spin-incoherent Luttinger liquid regimes.

Adiabatic frequency conversion (AFC) in microring resonators is a promising alternative for integrated, tunable frequency shifting of optical signals. However, the efficiency of AFC in a single-ring resonator is limited to below 80% for symmetric input pulses with a single peak. This is the consequence of a poor match between the pulse shape and the ring's impulse response. To overcome this limitation, we propose inducing AFC over two coupled rings rather than a single ring. We analyze the process's efficiency using temporal coupled mode theory (TCMT). We show that two-ring AFC can attain an efficiency of 97% in the limit of negligible intrinsic ring loss. To explain this higher AFC efficiency, we analyze two-ring AFC as a linear operator of rank two in the vector space of finite-energy pulses. We represent the AFC operator as a $2\times 2$ matrix and examine its singular value decomposition. In this way we analyze the dependence of the two-ring AFC efficiency on the input pulse shape and the TCMT parameters.

A waveguide coupler under periodically cascaded dielectric modulation is proposed to generate a Floquet lattice in synthetic frequency dimension. The Floquet bands may hold linear in the entire Brillouin zone, referred to as Floquet Dirac bands and giving rise to nondiffracting frequency shifts. The direction of frequency shift depends on the component of incident transverse modes, analogous to the spin-momentum locking realized in driven ultracold atoms recently. Furthermore, the shape of Floquet bands can be flexibly adjusted by applying external modulation voltage, resulting in a tunable group velocity and diffraction coefficient. The discrete diffraction and dynamic localization are also demonstrated in the Floquet frequency lattice. The study provides a versatile platform to explore multiband Floquet lattice physics in synthetic dimensions, and may find applications in spectral manipulation, mode conversion, and mode-division demultiplexing.

The increased decay rate of a two-level system weakly coupled to an optical cavity, known as the Purcell effect, is a cornerstone of cavity QED. However, the effect of cavity coupling is not well understood if the two-level system is replaced by a multilevel interacting system. Motivated by experiments looking to characterize molecular systems via exploiting a cavity interaction, we study a manifestation of the Purcell effect in a bio-inspired photosynthetic dimer. We focus in particular on how molecular vibrational modes, thought to play an important role in photosynthetic exciton transport, impact the system-cavity behavior in the Purcell regime. We provide a theoretical picture in terms of an effective non-Hermitian Hamiltonian, which extends the simple picture of a Jaynes-Cummings model to the description of a “multilevel” Purcell effect, where different levels have differing Purcell factors, with effective cooperativities mediated by coherent vibrational interactions.

A theory of phase-matched cascade correlated emission is developed based on a source field approach. An ensemble of three-level atoms is prepared in a phased state for which the probability to have two excitations is negligibly small. The field intensity radiated on each of the transitions is calculated. The radiation on the upper transition is isotropic and unpolarized, but the phase-matched component on the lower transition can be directional and polarized. Moreover, for sufficiently high optical densities, the emission on the lower transition can be superradiant. In addition to the field intensities, the joint probability for emission on both transitions is calculated, exhibiting correlations in both the directions of emission and polarization of the fields.

Recently, significant progress has been made in the demonstration of single-qutrit and coupled-qutrit gates with superconducting circuits. Coupled-qutrit gates have significantly lower fidelity than single-qutrit gates, owing to long implementation times. We present a protocol to implement the CZ universal gate for two qutrits based on a decomposition involving two partial-state swaps and local operations. The partial-state swaps can be implemented effectively using parametric coupling, which is fast and has the advantage of frequency selectivity. We perform a detailed analysis of this protocol in a system consisting of two fixed-frequency transmons coupled by a flux-tunable transmon. The application of an AC flux in the tunable transmon controls the parametric gates. This protocol has the potential to lead to fast and scalable two-qutrit gates in superconducting circuit architectures.

The possibility of attaining chiral edge modes under periodic driving has spurred tremendous attention both theoretically and experimentally, especially in light of anomalous Floquet topological phases that feature vanishing Chern numbers unlike any static counterpart. We consider here a periodically modulated honeycomb lattice and experimentally relevant driving protocols, which allows us to obtain edge modes of various character in a simple model. We calculate the phase diagram over a wide range of parameters and recover an anomalous topological phase with quasienergy gaps harboring edge states with opposite chirality. Motivated by the advances in single-site control in optical lattices, we investigate wave-packet dynamics localized at the edges in distinct Floquet topological regimes that cannot be achieved in equilibrium. We analyze transport properties in edge modes which originate from the same bands but with support at different quasienergies and sublattices as well as possessing different chiralities. We find that an anomalous Floquet topological phase can in general generate more robust chiral edge motion than a Haldane phase, allowing for more effective loading of the wave packet into edge channels. Our results demonstrate that the rich interplay of wave-packet dynamics and topological edge states can serve as a versatile tool in ultracold quantum gases in optical lattices.

Young's double-slit interference experiment is central to quantum mechanics. While it has been demonstrated that an array of atoms can produce interference in light, it is a fundamental question to ask whether a single atom can act as a double slit when prepared in a superposition of two separate positions. Cohen-Tannoudji et al. [Proceedings of the Tenth International Conference on Laser Spectroscopy, edited by M. Ducloy, E. Giacobino, and G. Camy (World Scientific, Singapore, 1992), pp. 3–14] showed that the cross section of the light scattered by a single atom is independent of the spatial separation. In this work, however, we show that when a single atom tunneling in a double well is coupled to an optical ring cavity, the interference phenomena arise if the tunneling rate is comparable to the cavity linewidth. Being driven by an external laser in the dispersive regime, the field emitted by the atom into the cavity exhibits an interference pattern when varying the double-well spacing. Super-Poissonian bunched light can also be generated near the destructive interference. Furthermore, we show that the atomic flux of the coherent tunneling motion generates directional cavity emission, which oscillates for many cycles before the decoherence of the atomic motion and the decay of the cavity photons. Our work opens ways to manipulate photons with controllable external states of atoms for quantum information applications and use cavity light as nondestructive measurements for many-body states of atomic systems.

We compute the quantum maximal correlation for bipartite Gaussian states of continuous-variable systems. Quantum maximal correlation is a measure of correlation with the monotonicity and tensorization properties that can be used to study whether an arbitrary number of copies of a resource state can be locally transformed into a target state without classical communication, known as the local state transformation problem. We show that the required optimization for computing the quantum maximal correlation of Gaussian states can be restricted to local operators that are linear in terms of phase-space quadrature operators. This allows us to derive a closed-form expression for the quantum maximal correlation in terms of the covariance matrix of Gaussian states. Moreover, we define Gaussian maximal correlation based on considering the class of local Hermitian operators that are linear in terms of phase-space quadrature operators associated with local homodyne measurements. This measure satisfies the tensorization property and can be used for the Gaussian version of the local state transformation problem when both resource and target states are Gaussian. We also generalize these measures to the multipartite case. Specifically, we define the quantum maximal correlation ribbon and then characterize it for multipartite Gaussian states.

Analyzing the properties of complex quantum systems is crucial for further development of quantum devices, yet this task is typically challenging and demanding with respect to the required amount of measurements. Special attention to this problem appears within the context of characterizing outcomes of noisy intermediate-scale quantum devices, which produce quantum states with specific properties so that it is expected to be hard to simulate such states using classical resources. In this work, we address the problem of characterization of a boson sampling device, which uses the interference of input photons to produce samples of nontrivial probability distributions that at certain condition are hard to obtain classically. For realistic experimental conditions the problem is to probe multiphoton interference with a limited number of the measurement outcomes without collisions and repetitions. By constructing networks on the measurement outcomes, we demonstrate the possibility to discriminate between regimes of indistinguishable and distinguishable bosons by quantifying the structures of the corresponding networks. Based on this, we propose a machine-learning-based protocol to benchmark a boson sampler with unknown scattering matrix. Notably, the protocol works in the most challenging regimes of having a very limited number of bitstrings without collisions and repetitions. As we expect, our framework can be directly applied for characterizing boson sampling devices that are currently available in experiments.

A satellite-based scheme to perform clock synchronization between ground stations spread across the globe using quantum resources was proposed in [Phys. Rev. A 107, 022615 (2023).] based on a quantum clock synchronization (QCS) protocol. Such a scheme could achieve synchronization up to the picosecond level over distances of thousands of kilometers. Nonetheless, the implementation of this QCS protocol has yet to be demonstrated experimentally in situations where the satellite velocities cannot be neglected, as is the case in many realistic scenarios. In this work, we develop analytical and numerical tools to study the effect of the relative velocity between the satellite and ground stations on the success of the QCS protocol. We conclude that the protocol can still run successfully if the data-acquisition window is chosen appropriately. As a demonstration, we simulate the synchronization outcomes for cities across the continental United States using a single satellite in a low earth orbit, low-cost entanglement sources, portable atomic clocks, and avalanche detectors. We conclude that, after including the effect of relative motion, subnanosecond- to picosecond-level precision can still be achieved over distance scales of $\approx 4000$ km. Such high-precision synchronization is currently not achievable over long distances ($\gtrsim 100\text{km}$) with standard classical techniques including the GPS. The simulation tools developed in this work are in principle applicable to other means of synchronizing clocks using entangled photons, which are expected to form the basis of future quantum networks like the quantum internet, distributed quantum sensing, and the quantum GPS.

Distributing entanglement among multiple users is a fundamental problem in quantum networks, requiring an efficient solution. In this work, a protocol is proposed for extracting maximally entangled ($|{\text{GHZ}}_n\rangle$) states for any number of parties in a quantum network. It is based on the graph-state formalism and requires minimal assumptions on the network state. The protocol only requires local measurements at the network nodes and just a single-qubit memory per user. Existing protocols on bipartite entanglement routing are also improved for specific nearest-neighbor network architectures. To this end, the concept of majorization is utilized to establish a hierarchy among different paths in a network based on their efficacy. This approach utilizes the symmetry of the underlying graph state to obtain better-performing algorithms.

We show the system of a heavy charged particle and a neutral atom can be described by a low-energy effective field theory where the attractive $1/r^4$ induced dipole potential determines the long-distance, low-energy wave functions. The $1/r^4$ interaction is renormalized by a contact interaction at leading order. Derivative corrections to that contact interaction give rise to higher-order terms. We show that this “induced-dipole EFT” (ID-EFT) reproduces the ${\pi }^{+}$-hydrogen phase shifts of a more microscopic potential, the Temkin-Lamkin potential, over a wide range of energies. Already at leading order it also describes the highest-lying excited bound states of the pionic-hydrogen ion. Lower-lying bound states receive substantial corrections at next-to-leading order, with the size of the correction proportional to their distance from the scattering threshold. Our next-to-leading order calculation shows that the three highest-lying bound states of the Temkin-Lamkin potential are well described in ID-EFT.

The angular distribution of attosecond Wigner time delay has been investigated including both quadrupole and relativistic effects using the relativistic-random-phase approximation that is based on the Dirac equation and includes significant aspects of many-body correlations. The results show a dramatic evolution of the time delay from (essentially nonrelativistic) dipole to quadrupole and spin-flip dynamics as a function of angle, thereby providing a venue for studying these interactions at the attosecond level.

The observation of molecular rotational dynamics induced by ultrashort laser pulses is of both fundamental and practical importance. Here, we develop an extended weak-field polarization method that allows us to visualize the two-dimensional spatial rotation of molecules. By manipulating the polarization direction of the pump pulse, this method allows for characterizing the rotational dependence on the azimuth angle when a weak probe pulse is present. To demonstrate this experimental scheme, we examine two types of pump pulses: (1) a linearly polarized pulse and (2) temporally delayed double pulses polarized at an angle of $\pi /4$, which are respectively applied to gas-phase molecules ${\mathrm{N}}_2\mathrm{O}$ at room temperature. The results show that this approach effectively captures the induced impulsive alignment and unidirectional rotation. By solving the time-dependent Liouville equation governing the molecules' behavior under the influence of the polarization-skewed pump pulses, we gain further insights into the mechanisms for generating unidirectional rotation. This work holds promising potential in the detection of two- and three-dimensional rotational dynamics of molecules like enantiomers and superrotors.

We investigate the hardcore Bose-Hubbard model on a honeycomb lattice under a pseudo-magnetic field generated by triaxial strain using the quantum Monte Carlo (QMC) method. In the presence of strain, we construct a phase diagram that encompasses superfluid and solid phases at different fillings. Interestingly, we observe intriguing phenomena related to filling factors, including a solid phase with a filling of $\rho =0.4912$. This solid phase is characterized by distinct sublattice occupancies separated by large domain walls. Additionally, within the superfluid region, we observe stripe phases where the occupancy of hardcore bosons exhibits oscillatory behavior. Finally, we employ linear spin-wave theory and derive the pseudo-Landau levels present in the excitation spectrum. Our findings not only provide valuable insights into the behavior of hardcore bosons in the presence of pseudo-magnetic fields, but they can also be experimentally realized using ultracold bosonic atoms confined in optical lattices.

We study the atom-dimer collision reaction for a three bosonic ${}^7\mathrm{Li}$ system using a multichannel model. We calculate the atom-dimer scattering length and dimer relaxation rate for all three ${}^7\mathrm{Li}$ atoms in $|f=1,m_f=1\rangle$ (case I) or $|f=1,m_f=0\rangle$ (case II) in an external magnetic field. The dimer is considered as the Feshbach dimer in both cases. In case I there are two atom-dimer resonances, whereas in case II only one atom-dimer resonance induced by the second excited trimer state is observed. It is found that $d$-wave two-body interaction plays an appreciable role in the entire considered magnetic field regime in case I but only when $B>$ 890 G in case II. We calculate the state-to-state transition probability and normalized transition probability from the incoming atom-dimer channel to the deep atom-dimer hyperfine channel. A propensity that the second-deepest hyperfine channels of atom-dimer collision reaction are dominant in all product channels is revealed for both $s$- and $d$-wave dimers.

We consider a spin impurity with multiple energy levels moving in a noninteracting Fermi sea and theoretically solve this Fermi-spin-polaron problem at nonzero temperature by using a non-self-consistent many-body $T$-matrix theory. We focus on the simplest case with spin $\frac{1}{2}$, where the two energy states of the impurity are coupled by a Rabi flip term. At small Rabi coupling, the impurity exhibits damped Rabi oscillations, where the decoherence is caused by the interaction with the Fermi sea, as recently reported in Fermi-polaron experiments with ultracold atoms. We investigate the dependence of Rabi oscillations on the Rabi coupling strength and examine the additional nonlinear damping due to large Rabi coupling. At finite temperature and nonzero impurity concentration, the impurity can acquire a pronounced momentum distribution. We show that the momentum or thermal average can sizably reduce the visibility of Rabi oscillations. We compare our theoretical predictions to recent experimental data and find good agreement without any adjustable parameters.