The collective charge of $N$ two-level atoms interacting in an open system is investigated. In contrast to a no atomic dissipation quantum battery, the battery remains at a steady state after reaching the moment of full charge. Considering the interactions between atoms, we find that the energy storage of quantum batteries will be significantly enhanced with the increase of atomic repulsion, and the attraction between atoms will exacerbate the dissipation of batteries in the environment. We extend this conclusion to two-level batteries in the drive field and three-level atom quantum batteries. In addition, we also investigate the dissipative charging process of multiatom quantum batteries and find that the number of atoms during the charging process can to some extent affect the energy conversion efficiency during the charging process. Under extreme conditions, the inverse temperature $\beta$ can disrupt the energy storage of the battery.

Error-correction codes are central for fault-tolerant information processing. Here we develop a rigorous framework to describe various coding models based on quantum resource theory of superchannels. We find, by treating codings as superchannels, a hierarchy of coding models can be established, including the entanglement assisted or unassisted settings, and their local versions. We show that these coding models can be used to classify error-correction codes and accommodate different computation and communication settings depending on the data type, side channels, and pre-/postprocessing. We believe the coding hierarchy could also inspire new coding models and error-correction methods.

We analyze a general bipartite-like representation of arbitrary pure states of N indistinguishable partcles, valid for both bosons and fermions, based on $M$- and $(N-M)$-particle states. It leads to exact $(M,N-M)$ Schmidt-like expansions of the state for any $M<N$ and is directly related to the isospectral reduced $M$- and $(N-M)$-body density matrices ${\rho }^{\left(M\right)}$ and ${\rho }^{(N-M)}$. The formalism also allows for reduced yet still exact Schmidt-like decompositions associated with blocks of these densities, in systems having a fixed fraction of the particles in some single-particle subspace. Monotonicity of the ensuing $M$-body entanglement under a certain set of quantum operations is also discussed. Illustrative examples in fermionic and bosonic systems with pairing correlations are provided, which show that in the presence of dominant eigenvalues in ${\rho }^{\left(M\right)}$, approximations based on a few terms of the pertinent Schmidt expansion can provide a reliable description of the state. The associated one- and two-body entanglement spectrum and entropies are also analyzed.

The accurate and robust estimation of quantum process properties is crucial for quantum information processing and many-body physics. Combining classical shadow tomography and randomized benchmarking, Helsen et al. introduced a method to estimate the linear properties of quantum processes. In this work, we focus on the estimation protocols of nonlinear process properties that are robust to state preparation and measurement errors. We introduce two protocols, both utilizing random gate sequences but employing different postprocessing methods, which make them suitable for measuring different nonlinear properties. The first protocol offers a robust and sound method to estimate the out-of-time-ordered correlation, as demonstrated numerically in an Ising model. The second protocol estimates unitarity, effectively characterizing the incoherence of quantum channels. We expect the two protocols to be useful tools for exploring quantum many-body physics and characterizing quantum processes.

Current noisy intermediate-scale quantum (NISQ) trapped-ion devices are subject to errors which can significantly impact the accuracy of calculations if left unchecked. A form of error mitigation called zero noise extrapolation (ZNE) can decrease an algorithm's sensitivity to these errors without increasing the number of required qubits. Here we explore different methods for integrating this error mitigation technique into the Variational Quantum Eigensolver (VQE) algorithm for calculating the ground state of the ${\text{HeH}}^{+}$ molecule at $0.8\text{Å}$ in the presence of experimental noise. Using the Quantum Scientific Computing Open User Testbed (QSCOUT) trapped-ion device, we test three methods of scaling noise for extrapolation: time stretching the two-qubit gates, scaling the sideband detuning parameter, and inserting two-qubit gate identity operations into the ansatz circuit. We find that time stretching and sideband detuning scaling fail to scale the noise on our particular hardware in a way that can be extrapolated to zero noise. Scaling our noise with global gate identity insertions and extrapolating after variational optimization, we achieve error suppression of $96.8\%$, resulting in an energy estimate within $-0.004\pm 0.04$ hartree of the ground state energy. This is an improvement, but still outside the chemical accuracy threshold of 0.0016 hartree. Our results show that the efficacy of this error mitigation technique depends on choosing the correct implementation for a given device architecture.

We present a systematic study of quantum sensing of ultralow temperature in biwire ultracold polar molecules of a quasi-one-dimensional (1D) trap by exploring the dynamics of two physically different qubit models. The two models consist of a trapped impurity atom that act as a temperature quantum sensor interacting with polar molecules reservoir, where dipole moments are aligned head-to-tail across the wires. Our model takes advantage of the adjustable interwire distance to accurately control the precision ultralow temperatures measurement. We show that the system undergoes a transition from Markovian to non-Markovian dynamics, which can be controlled by changing the interwire separation, the dipole-–dipole interaction (DDI), and the temperature. We characterize the thermometric performance using the quantum signal-to-noise ratio for both models and demonstrate that such a quantity exhibits a higher peak at ultralow temperature. We therefore emphasize that ultracold polar molecules are crucial for revolutionizing temperature sensing.

Periodic driving has emerged as a powerful tool to control, engineer, and characterize many-body quantum systems. However, the required pulse sequences are often complex, long, or require the ability to control the individual degrees of freedom. In this work, we study how a simple Carr-Purcell–Meiboom-Gill (CPMG)-like pulse sequence can be leveraged to enhance the coherence of a large ensemble of spin qubits and serve as an important characterization tool. We implement the periodic drive on an ensemble of dense nitrogen-vacancy (NV) centers in diamond and examine the effect of pulse rotation offset as a control parameter on the dynamics. We use a single diamond sample prepared with several spots of varying NV density, which, in turn, varies the NV-NV dipolar interaction strength. Counterintuitively, we find that rotation offsets deviating from the ideal $\pi$ pulse in the CPMG sequence (often classified as pulse errors) play a critical role in preserving coherence along an axis set by the $\pi$ pulses even at nominally zero rotation offset. The cause of the coherence preservation is an emergent effective field that scales linearly with the magnitude of the rotation offset for small offsets. In addition to extending coherence, we compare the rotation offset dependence of coherence to numerical simulations to measure the disorder and dipolar contributions to the Hamiltonian to quantitatively extract the densities of the constituent spin species within the diamond.

A unified treatment of atomic excitation and ionization in ion-atom collisions is proposed. It is demonstrated that the state-resolved excitation cross sections multiplied by $n^3$, where $n$ is the principal quantum number of the excited state, and the corresponding partial singly differential ionization cross section form two parts of a single continuous function. This allows one to obtain the excitation cross section for any state including high-lying Rydberg states and the energy-differential ionization cross section at, and arbitrarily close to, the threshold. The proposed method can be used in any theoretical approaches to excitation and ionization and experimental measurements.

We analyze the projected sensitivity of a laboratory-scale ytterbium atom interferometer to scalar, vector, and pseudoscalar dark matter signals. A frequency ratio measurement between two transitions in ${}^{171}\mathrm{Yb}$ enables a search for variations of the fine-structure constant that could surpass existing limits by a factor of 100 in the mass range ${10}^{-22}$–${10}^{-16}$ eV. Differential accelerometry between ytterbium isotopes yields projected sensitivities to scalar and vector dark matter couplings that are stronger than the limits set by the MICROSCOPE equivalence principle test, and an analogous measurement in the MAGIS-100 long-baseline interferometer would be more sensitive than previous bounds by factors of 10 or more. A search for anomalous spin torque in MAGIS-100 is projected to reach similar sensitivity to atomic magnetometry experiments. We discuss strategies for mitigating the main systematic effects in each measurement. These results indicate that improved dark matter searches with ytterbium atom interferometry are technically feasible.

A feasibility study is done for the possibility of a universal set of quantum gate implementation based on phononic state via fourth-order Duffing nonlinearity in an optomechanical system. The optomechanical system consists of $N$ doubly clamped coupled nanobeam arrays driven by local static and radio frequency electrical potentials, coupled to a single-mode high-finesse optical cavity. The results show that the ideal cnot gate can be implemented only under nonresonance dynamics when the dissipation processes are negligible.

We report on saturated absorption spectroscopy measurements of the $\left(4s^2\right){}^{1}S_0\to \left(4s4p\right){}^{1}P_1$ transition for the four most abundant even-mass isotopes in calcium. By referencing the laser locked to an ultralow expansion cavity and carefully investigating systematic errors, isotope shifts are determined with a precision below $100\mathrm{k}\mathrm{Hz}$, improving previously reported values by a factor of about 3. A King plot analysis, employing literature values of the 729-$\mathrm{n}\mathrm{m}$ transition in ${\mathrm{Ca}}^{+}$ ions, shows excellent linearity. The field and mass shift parameters are determined from King plots with other transitions.

Fully describing light propagation in a rotating, anisotropic medium with thermal nonlinearity requires modeling the interplay between nonlinear refraction, birefringence, and the nonlinear group index. Incorporating these factors into a generalized coupled nonlinear Schrödinger equation and fitting them to recent experimental results reveals two key relationships: the photon drag effect can have a nonlinear component that is dependent on the motion of the medium, and the temporal dynamics of the moving birefringent nonlinear medium create distorted figure-eight-like transverse trajectories at the output. The beam trajectory can be accurately modeled with a full understanding of the propagation effects. Efficiently modeling these effects and accurately predicting the beam's output position has implications for optimizing applications in velocimetry and beam steering. Understanding the roles of competitive nonlinearities gives insight into the creation or suppression of nonlinear phenomena like self-action effects.

Phenomena involving interactions among magnons, phonons, and photons in cavity magnomechanical systems have attracted considerable attention recently, owing to their potential applications in the microwave frequency range. One such important effect is the response of a probe field to such a tripartite interaction between photon-magnon-phonon. In this paper we study the Goos-Hänchen shift (GHS) of a reflected probe field in a cavity magnomechanical system. We consider a yttrium iron garnet (YIG) sphere positioned within a microwave cavity. A microwave control field directly drives the magnon mode in the YIG sphere, whereas the cavity is driven via a weak probe field. Our results show that the GHS can be coherently controlled through magnon-phonon coupling via the control field. For instance, the GHS can be tuned from positive to negative by tuning the magnon-phonon coupling. Similarly, the effective cavity detuning is another important controlling parameter for the GHS. Furthermore, we observe that the enhancement of the GHS occurs when magnon-phonon coupling is weak at resonance and when the magnon-photon coupling is approximately equal to the loss of microwave photons. Our findings may have potential significance in applications related to microwave switching and sensing.

We demonstrate the feasibility of implementing a photon source with sub-Poissonian emission statistics through temporal multiplexing of a continuous wave heralded photon source in the optical communications wavelength range. We use the time arrival information of a heralding photon to actively modify the delay of the heralded photon in an all-fiber assembly, in order to synchronize the output with respect to an external clock. Within this synchronized operating regime we show that the addition of a single temporal correcting stage can improve the figure of merit for single-photon emission of a heralded photon source. We obtain a brightness improvement factor of approximately 1.8 and an enhancement of the signal-to-noise ratio, quantified by the coincidence-to-accidental counts ratio. These results clear the way for integrated optics nonclassical photon sources in the optical communication band.

The geometric quantum discord of a two-qudit state has been studied in many papers; however, its exact analytical value in the explicit form is known only for a general two-qubit state, a general qubit-qudit state, and some special families of two-qudit states. Based on the general Bloch vectors formalism [E. R. Loubenets et al., J. Phys. A: Math. Theor. 54, 195301 (2021)], we find the explicit exact analytical value of the geometric quantum discord for an arbitrary two-qudit state of any dimension via the parameters of its correlation matrix and the Bloch vectors of its reduced states. This general analytical result includes all the known exact results on the geometric quantum discord only as particular cases and proves rigorously that the lower bound on the geometric discord presented in [S. Rana et al., Phys. Rev. A 85, 024102 (2012)] constitutes its exact value for each two-qudit state. Moreover, our general result allows us to find for an arbitrary two-qudit state, pure or mixed, the upper and lower bounds on its geometric quantum discord, expressed via the Hilbert space characteristics of this state.

State preparation is a fundamental routine in quantum computation, for which many algorithms have been proposed. Among them, perhaps the simplest one is the Grover-Rudolph algorithm. In this paper we analyze the performance of this algorithm when the state to prepare is sparse. We show that the gate complexity is linear in the number of nonzero amplitudes in the state and quadratic in the number of qubits. We then introduce a simple modification of the algorithm, which makes the dependence on the number of qubits also linear. This is competitive with the best known algorithms for sparse state preparation.

As one kind of ubiquitous collision system, ${\mathrm{O}}^{6+}+\mathrm{He}$ deserves attentive study due to its theoretical significance in fundamental physics and applied value in fields like astrophysics or plasma physics. Specifically, in the case of the electron capture process, while a considerable number of measurements and calculations have focused on single electron capture, research is still inadequate on the double electron capture which contributes nearly 10% to the overall electron capture. In this work, a two-active-electron semiclassical asymptotic-state close-coupling method is used to calculate the total and $l-\mathrm{resolved}$ state-selective double electron capture cross sections of ${\mathrm{O}}^{6+}+\mathrm{He}$ collisions in the energy range 0.5–100 keV/u, accompanied by experimental measurements in the energy range 2.63–37.5 keV/u with an uncertainty of 16%, in good consistency. These theoretical and experimental data can fill gaps in the database of double electron capture in ${\mathrm{O}}^{6+}+\mathrm{He}$ collisions and provide insights for improving theoretical models in further research.

We have measured transition frequencies, isotope shifts, and hyperfine-structure splittings in the $3d^2{(}^{3}F)4s{}^4{F}_J\to 3d^2{(}^{3}F)4p{}^4{G}_{J+1}^o$ transitions in stable ${\mathrm{Ti}}^{+}$ ions for $J=\frac{3}{2},\frac{5}{2},\frac{7}{2}$ using collinear laser spectroscopy. Ions were generated by laser ablation in a buffer-gas atmosphere and extracted into vacuum through a nozzle and a pair of radio-frequency funnels. The results obtained are of interest as reference values for on-line measurements of short-lived titanium isotopes and for astrophysical searches for temporal or spatial variations of the fine-structure constant $\alpha$ using quasar absorption spectra.

The motion of atoms through a magnetic field (due to a change in reference frame) will result in an additional electric field felt by the electrons in that atom. The motional Stark effect is a well-established effect that has been approximately included in calculations of spectra of magnetized plasmas, usually through diagonalizing the Hamiltonian. The motional Stark effect for continuum states is poorly defined due to an overlap integral that results in a Dirac delta function. This paper presents a workaround by evaluating the motional Stark effect in the Green's function within the scattering formalism. We report on some results pertaining to bound-free spectra for white dwarf and neutron star magnetic field strengths. In most cases, resonances in the continuum are shifted and broadened. This behavior has the effect of raising the Rosseland mean opacity in white dwarfs and neutron star atmospheres.