The permutation symmetry is a fundamental attribute of the collective wave function of indistinguishable particles. It makes a difference for the behavior of collective systems having different quantum statistics but existing in the same environment. Here we show that for some specific quantum conjugation between the spin and spatial degrees of freedom the indistinguishable particles can behave similarly for either quantum statistics. In particular, a mesoscopically scaled collection of atomic qubits, mediated by optical tweezers, can model the behavior of a valent electronic shell compounded with nuclear centers in molecules. This makes possible quantum simulations of mono- and divalent bonds in quantum chemistry by manipulation of up to four bosonic atoms confined with optical microtraps.

Tagging barium ions in double-beta decay experiments involving ${}^{136}\mathrm{Xe}$ atoms offers a promising pathway to achieving an almost background-free environment, which is essential for addressing key unresolved questions in neutrino physics, such as the nature of neutrinos and their mass hierarchy. In this manuscript, I present a detection scheme that relies exclusively on the intrinsic energy levels of the barium ion. This method is based solely on the optical interrogation of its electronic transitions, avoiding the need for additional additives or fluorescent agents in the xenon vessel and thereby simplifying the experimental setup. Throughout the manuscript, I demonstrate the feasibility of this detection concept through numerical simulations under realistic experimental conditions inspired by the Neutrino Experiment with a Xenon TPC experiment. The results show that the fluorescence signature of the barium ion can be reliably detected, indicating that the proposed method is a viable path toward background-free searches for neutrinoless double-beta decay.

The photonic spin Hall effect, a result of spin-orbit interaction, has attracted significant interest because of its fundamental importance and potential applications. However, optical losses are ubiquitous, which hampers the enhancement of photonic spin Hall shift (PSHS). In this work, we consider an atomic medium that exhibits both absorption and transparency to investigate and mitigate the effects of loss on PSHS. We demonstrate that laser-induced coherence in an atomic medium, leading to electromagnetically induced transparency (EIT) at resonance, counteracts the detrimental effects of losses on the PSHS. Upon EIT at resonance in a coherent medium enclosed within dielectric slabs, zero reflectivity of the incident polarized state is restored at an incident angle defined by the conventional Brewster's angle to enhance PSHS. Moreover, the tunable refractive index of the atomic medium enables manipulation of PSHS without structural modifications with a tiny loss. Our proposed loss-free approach to PSHS may enable advanced optical sensing and other spin-based applications.

The electron spin in semiconductor quantum dots is a promising candidate for scalable quantum information processing. However, a critical and challenging step is achieving high-fidelity control and entanglement between spatially separated spin qubits. Here we propose a scheme for implementing entangling gates between two long-distance spin qubits based on the resonator-induced phase. Since the scheme only requires microwave control of the resonator, the spin qubits can operate at their sweet spots and exhibit high-frequency flexibility. We investigate the coherent dynamics of the resonator-induced phase gate and demonstrate the potential to achieve a controlled-$Z$ gate with a high fidelity of 93.5% within a short timescale of tens of nanoseconds under realistic conditions. We also show the robustness of this scheme with respect to perturbations in the control pulse parameters. Furthermore, our scheme can be used to generate nonlocal entangled states and can be easily extended to multiqubit architectures. These results provide strong support for the realization of large-scale quantum computing with spin qubits.

Optomechanical sensors are capable of transducing external perturbations to resolvable optical signals. A particular regime of interest is that of high-bandwidth force detection, where an impulse is delivered to the system over a short period of time. Exceedingly sensitive impulse detection has been proposed to observe very weak signals like those due to long-range interactions with dark matter that require much higher sensitivities than current sensors can provide. Quantum resources to go beyond the traditional standard quantum limit of these sensors include squeezing of the light used to transduce the signal, backaction evasion by measuring the optimal quadrature, and quantum nondemolition (QND) measurements that reduce backaction directly. These methods have been developed in the context of gravitational wave detection for target frequencies in the audio band range. Here, we provide the theoretical limits to quantum noise reduction for higher and broader frequency targets, such as those from dark matter signals, while combining quantum-enhanced readout techniques based on squeezed light and QND measurements with optomechanical sensors. We demonstrate that backaction evasion through QND techniques dramatically reduces the technical challenges presented when using squeezed light for broadband force detection, paving the way for combining multiple quantum noise reduction techniques for enhanced sensitivity in the context of impulse metrology.

We present first-principles numerical simulations of photoionization in neon induced by bichromatic extreme ultraviolet pulses with frequencies $\omega$ and $2\omega$, specially chosen to make $\omega$ equal to the energy difference between the $2s$ and $2p$ subshells. This allows for the production of photoelectrons from the $2s$ shell by the $2\omega$ pulse and from the $2p$ shell by the $\omega$ pulse with the same energy. Using the multiconfigurational time-dependent Hartree-Fock method, we explore how Rabi coupling between subshells generates coherence between the corresponding photoelectron wave packets. Our ab initio calculations confirm the analytical results derived from the essential-states approach in Ishikawa et al., [J. Phys. Chem. A 127, 10638 (2023)], validating the theoretical predictions. Although we focus on the Ne $2p$ and $2s$ subshells, our approach is applicable to a broad range of systems exhibiting photoionization from multiple subshells. The laser parameters employed in our simulations are available in modern free electron lasers (FELs), and we anticipate that this work could stimulate experimental investigations using FELs to study ion-photoelectron coherence and entanglement.

In phase estimation via quantum interferometry, measurement precision is governed by the quantum state and the measurement strategy. Nonlinear SU(1,1) interferometers prepare entangled states that have been shown to enable Heisenberg-limit precision. In previous work, we developed the optimal measurement scheme, which saturates the ultimate limit in ab initio phase estimation, avoiding the issue of ambiguity. However, realizing this scheme is highly nontrivial and involves measurements beyond the photon-number operator. In this study, we propose a probabilistic measurement scheme capable of realizing the optimal measurement scheme with a success rate of 50% through postselection. This method allows us to achieve Heisenberg-scaling precision but it is suboptimal with respect to saturation of the quantum Cramér-Rao bound. It utilizes projection synthesis by introducing an ancillary optical mode prepared in a superposition state, combined with standard photon-number-resolving detection. This approach provides insights into the physical realization of optimal measurement strategies in nonlinear interferometers, with implications for quantum precision measurement in general.

A mathematical description of the reduced dynamics of an open quantum system can often be given in terms of a completely positive and trace-preserving map, also known as a quantum channel. In a seminal work by Wolf et al. [Phys. Rev. Lett. 101, 150402 (2008)], it was shown that deciding whether a given quantum channel was generated from an underlying effective Markovian dynamics, with time-independent generator of Lindblad form, is generally an NP-hard problem. The difficulty is related to the fact that one has to search through all possible branches of the operator logarithm of the map in order to identify if any of the resulting effective generators is of Lindblad form. In this work we show that in cases where one has access to the full reduced dynamics at all previous times (the dynamical map) one can significantly facilitate the search for an effective generator by making use of Floquet theory. By performing a spectral unwinding such that the effective micromotion is minimized, the effective Floquet generator is often an excellent candidate for an effective generator of Lindblad form. This significantly reduces the complexity of the search for an effective Lindbladian in many (though not all) cases. Our results are relevant for engineering Floquet Lindbladians in complex many-body systems.

We show that the Kirkwood-Dirac quasiprobability distributions can detect the presence of quantum resources in all convex resource theories via strictly negative probability outcomes. This negativity serves not only as a hallmark of resourcefulness in such theories, but also quantifies the geometric distance between a resourceful state and its closest free (i.e., nonresourceful) counterpart. Moreover, we demonstrate that these distributions can be rendered informationally complete, providing both a comprehensive description of the quantum state and a direct indicator of the underlying resource. We further discuss the relationship between convex resource theories, between strong anomalous weak values, and negative quasiprobabilities. Finally, by showing that negativity emerges only under measurement incompatibility, our results identify measurement incompatibility as a fundamental mechanism enabling quantum advantage in resourceful states.

A scheme is proposed for parallel teleportation of partially unknown quantum operations with multiple degrees of freedom based on a nitrogen-vacancy (NV) center system. An NV center system offers long coherence time and high fidelity for quantum operations. Assisted by the error heralded module and the corresponding circuit, high fidelity parallel teleportation of partially unknown quantum operations can be achieved, with hyperentangled Bell states of polarization and time-bin modes as the quantum channels. In the case of low side leakage and strong coupling, the efficiency and success probability approaching unity can be expectable. The employment of simple module circuits and optical components is beneficial for the implementation of the scheme with currently experimental techniques.

We theoretically demonstrate the effects of interferences and asymmetries between $K$ and $K^{\prime }$ valleys for pristine graphene in high-order harmonic generation (HHG) by a single-color laser pulse. It is shown that the allowed orders of the observed overall HHG spectra are attributed to the consequences of quantum interferences between $K$ and $K^{\prime }$ valleys. The cancellations of forbidden harmonics are caused by the destructive interferences between two different valleys due to the dynamical symmetries of the laser-solid systems. Apparent valley-contrasting and helicity-resolved harmonic signals can be observed for the $3k$-order ($k\in \mathbb{N}$) harmonics when the polarization state of the driving laser field slightly deviates from the ideal circular polarization. The valley discriminations for these emerging $3k$-order ($k\in \mathbb{N}$) harmonics originate from the unequal responses of the HHG from two different valleys within the perturbation regime. In addition, the valley asymmetries of the electronic excitations are also observed by using an elliptically polarized laser pulse. Our work clearly illustrates the essential intervalley interplay in the HHG process for pristine graphene, facilitating the understanding of ultrafast electron dynamics in zero-band-gap materials.

We theoretically investigate the nonequilibrium dynamics of homogeneous ultracold Bose gases of microwave-shielded polar molecules following a sudden quench of the scattering length at zero temperature. We calculate in particular the quantum depletion, the anomalous density, the condensate fluctuations, and the pair-correlation function using both the time-dependent Bogoliubov approach and the self-consistent time-dependent Hartree-Fock-Bogoliubov approximation. During their time evolution, these quantities exhibit slow or fast oscillations depending on the strength of the shielding interactions. We find that at long timescales the molecular condensate is characterized by nonequilibrium steady-state momentum distribution functions, with depletion, anomalous density, and correlations that deviate from their corresponding equilibrium values. We demonstrate that the pair correlations expand diffusively at short times while they spread ballistically at long times.

We show that the physics of the $\mathrm{SU}(N$) Hubbard model can be realistically simulated with the recently developed orbital Hatsugai-Kohmoto model. In this approach, the momentum mixing absent from the band Hatsugai-Kohmoto model is included by grouping $n$-Hubbard atoms into a cluster. We take advantage of the rapid convergence of this scheme ($1/n^2$) and show that for $n\approx O\left(10\right)$, quantitative agreement with the determinantal quantum Monte Carlo method arises for the double occupancy as well as qualitative agreement for the filling and compressibility across the Mott transition. Additional features of this work are that we can obtain low-temperature physics, which could be qualitatively different from its high-temperature counterpart, and dynamical quantities without resorting to analytical continuation, thereby establishing the orbital Hatsugai-Kohmoto model as a useful alternative perspective for studying strong correlations in $\mathrm{SU}(N$) systems.

Moiré-related physics in twisted bilayer two-dimensional (2D) materials has attracted widespread interest in condensed-matter physics. Simulation of moiré related physics in cold atom platforms is expected to outperform 2D materials thanks to its advantage of higher tunablility. Here, we demonstrate that the cold atom platform enables an alternative mechanism of moiré lattice formation, induced by interlayer interaction with intrinsic “dynamical” character, in contrast with conventional moiré lattice induced by “static” ways such as single-particle interlayer tunneling. Specifically, we consider a twisted bilayer Bose-Hubbard model with vanishing interlayer tunneling, and the bilayer is solely coupled through interlayer interactions that originate from the contact interaction of atoms. We find that this system hosts a plethora of intriguing phases unique to this dynamical lattice, including a variety of Mott insulator (MI) and superfluid (SF) phases either preserving or breaking moiré lattice symmetry, phases with one layer in SF and the other in MI, “interlocked” MI, and self-localized phases at commensurate twist angles, which exhibits the characteristics of Bose glass and quasi-many-body localization in the absence of (quasi)disorder or quasicrystalline lattices. Our prediction can be readily observed in current experimental setups of twisted bilayer optical lattices, opening up alternative avenues for exploring the rich physics of interaction induced moiré systems in cold atoms.

Suppose you receive a sequence of qubits where each qubit is guaranteed to be in one of two pure states, but you do not know what those states are. Your task is to determine the states. This can be viewed as a kind of quantum state learning, or quantum state estimation. The problem is that, without more information, all that can be determined is the density matrix of the sequence and, in general, density matrices can be decomposed into pure states in many different ways. To solve the problem, additional information, either classical or quantum, is required. We show that if an additional copy of each qubit is supplied (that is, one receives pairs of qubits, both in the same state, rather than single qubits) the task can be accomplished. This is possible because the mixed two-qubit state has a unique decomposition into pure product states. For illustration purposes, we numerically simulate the symmetric, informationally complete measurement of a sequence of qubit pairs and show that the unknown states and their respective probabilities of occurrence can be inferred from the data with high accuracy. Finally, we propose an experiment that employs a product measurement and can be realized with existing technology, and we demonstrate how the data tell us the states and their probabilities. We find that it is enough to detect a few thousand qubit pairs.

We examine a system in which an impurity qubit is immersed in a quasi-two-dimensional dipolar Bose-Einstein condensate whose collective excitations act as a dephasing reservoir for the qubit. The relative dipole-dipole interaction strength is estimated by the probe qubit dephasing. The ultimate precision of this estimation is quantified by the quantum Fisher information (QFI), which can be obtained by means of measuring quantum coherence of the probe qubit. Our findings indicate that, in the interval where roton excitations appear, the QFI oscillates periodically with the evolution time $t$, and the amplitude of these oscillations increases alongside the extension of $t$. Moreover, we analytically determine that the envelope curve formed by the local maximum points satisfies the functional relationship $At+B{t}^{1/2}+C$ during long-term encoding scenarios, where $A, B$, and $C$ are positive numbers. It is revealed that the highly non-Markovian effects caused by the roton softening of the excitation spectrum allow long evolution time to serve as a resource for enhancing sensing precision. We also study the effects of the reservoir's temperature on the dynamics of the QFI. It is found that lower temperatures have virtually no effect, while higher temperatures can accelerate the growth rate of the QFI with evolution time, reflecting that thermal noise can be used to enhance the quantum advantage in quantum sensing. Our work provides a new pathway for enhancing the sensing precision of dephasing qubits.

We present a theoretical study of resonant elastic photon scattering by highly charged ions in the presence of external electric and magnetic fields. Special emphasis is placed on head-on collisions of relativistic ion beams and counterpropagating laser photons, as can be observed in ion storage ring experiments. If the collision zone for such a scenario is exposed to a moderate field of a dipole magnet, a fast-moving ion will be subjected to strong electric and magnetic fields in its rest frame due to the Lorentz transformation. To investigate the effect of these fields we performed detailed calculations for the elastic photon scattering by He-like Ca ions moving with the Lorentz factor ${\gamma }_L=2395$. Such a scenario is of particular interest for the Gamma Factory project which is supported by the CERN Physics Beyond Colliders framework. Based on the results of our calculations, we argue that even moderate magnetic fields significantly modify the rate of detected photons as well as their emission pattern and polarization. This sensitivity to external fields opens interesting avenues for diverse applications for the Gamma Factory project, such as resonance condition tuning, beam cooling, and polarization control.

Direct molecular simulation and the state-to-state method, as the prevailing theoretical approaches for studying thermally nonequilibrium molecular collisions, strongly rely on available high-precision potential energy surfaces and extensive trajectory calculations, and their application to polyatomic molecular systems remains a challenge. In this paper, the state-resolved deep potential molecular dynamics (SR-DPMD) method is proposed, which performs potential energy surface construction and molecular dynamics simulation based on the deep potential molecular dynamics scheme and then achieves energy state resolution during the simulation through normal mode analysis. Applying this method to the simulation of thermal nonequilibrium dynamics of the methane-nitrogen system and comparing it with the simulation of state-resolved ReaxFF, combining the energy state analysis of five-atom molecules is realized. The results demonstrate that vibration-rotation coupling and vibration-vibration coupling can directly affect the vibrational energy relaxation behavior of molecules. It is evident that the accuracy of the ReaxFF is inadequate to facilitate the energy state resolution of the molecule; however, it is capable of yielding qualitative outcomes concerning the energy relaxation of the molecule during the simulation. Overall, the SR-DPMD method provides a powerful tool for understanding the energy state evolution of polyatomic molecules under nonequilibrium conditions and is expected to provide valuable insights into energy relaxation, chemical reactions, and their coupling processes. The reaction force field is also dedicated to providing new perspectives for the study of thermal nonequilibrium dynamics.

The $g$ factors for $J=1$, $F=3/2$, $|M_F|=3/2$ hyperfine levels of the electronic ground state ${}^3\mathrm{\Delta }_1$ of the ${}^{232}\mathrm{ThF}^{+}$ cation were calculated as functions of the external electric field. These calculations were performed by diagonalizing the molecular Hamiltonian in the presence of the external electric field. The necessary matrix elements of the Hamiltonian were obtained by combining existing experimental data with ab initio calculations within the relativistic coupled-cluster theory. The calculated $g$-factor difference, $\mathrm{\Delta }g=2.3\times {10}^{-4}$, for the $\mathrm{\Omega }$ doublets is in good agreement with the experimental value $\left|\mathrm{\Delta }g\right|=3\left(3\right)\times {10}^{-4}$ [K. B. Ng et al., Phys. Rev. A 105, 022823 (2022)]. These calculations were used to analyze systematic effects and to develop methods for their suppression in the experiment aimed at searching for the electron electric dipole moment.