Semiconductor quantum dots provide a promising platform for spin qubit manipulation and quantum logic gate implementation, which are essential for scalable quantum computing architectures. In this work we utilize a variational quantum compiling algorithm to design efficient three-qubit gates using a time-independent Hamiltonian composed of only physical interaction terms. The resulting gates, including the Toffoli and Fredkin gates, demonstrate high fidelity and robustness against both coherent and incoherent noise sources, including charge and nuclear spin noise. This method is applicable to a wide range of physical systems, such as superconducting qubits and trapped ions, paving the way for more resilient and universal quantum computing architectures.

An electrospray ion source has been coupled to a cryogenic electrostatic ion-beam storage ring to enable experimental studies of the fundamental properties of biomolecular ions and their reactions in the gas phase on longer timescales than with previous instruments. Using this equipment, we have measured the vibrational radiative cooling rate of the deprotonated anion of the chromophore of the cyan fluorescent protein, a color-shifted mutant of the iconic green fluorescent protein. Time-resolved dissociation rates of collisionally activated ions are first measured to benchmark a model of the dissociation rate coefficient. Storage time-dependent laser-induced dissociation rates are then measured to probe the evolution of the internal energy distribution of the stored ion ensemble. We find that significant heating of the electrosprayed ions occurs upon their extraction from the ion source, and that the radiative cooling rate is consistent with the prediction of a simple harmonic cascade model of vibrational relaxation.

Calculating the out-of-equilibrium dynamics of many-body quantum systems theoretically is a challenging problem. Essentially exact results can be obtained for the out-of-equilibrium correlations in the Bose-Hubbard model in one dimension, but higher dimensions require approximate methods. One such method is the two-particle irreducible strong coupling (2PISC) approach [M. R. C. Fitzpatrick and M. P. Kennett, Nucl. Phys. B 930, 1 (2018)]. Calculations of the single-particle correlations using this method yield values of the velocity for correlation spreading that match well with exact methods in one dimension and experiments in one and two dimensions. However, the 2PISC method is less accurate for determining the amplitude of correlations, especially in the regime where interactions are not very strong. Viewing the calculation of the single-particle correlations as an image correction problem, we train a neural network (NN) to take input from the 2PISC approach to reproduce the output of exact diagonalization calculations. We show that the predictions of the NN improve on 2PISC results for parameters outside the training region. Our approach is not specific to the Bose-Hubbard model and may find application to the out-of-equilibrium dynamics of other quantum many-body systems.

We study theoretically the critical velocity $U_c$ for quantum vortex generation by a thin plate-shaped obstacle moving through a uniform two-dimensional Bose-Einstein condensate. Our results based on the Gross-Pitaevskii theory reveal that the critical velocity monotonically decreases with increasing the plate size $L$. In the limit of large $L$, the critical velocity is asymptotic to $L^{-1/2}$ predicted by the potential flow theory for an incompressible ideal fluid with a phenomenological length correction. As $L$ decreases, however, the incompressible analysis breaks down quantitatively. By performing a perturbative analysis to incorporate compressibility into the potential flow theory, we successfully reproduced the numerical results analytically over a wide parameter range.

We investigate the intrinsic anomalous linear and nonlinear Hall effect in a square optical lattice under the shaking. We find that the on-resonant shaking can induce a valley independent term which leads to the valley Hall effect. While the off-resonant shaking induces a valley-dependent term and the system shows an anomalous Hall effect. Furthermore, the nonlinear valley Hall effect also appears in this system, and the nonlinear valley Hall conductivities can be controlled by varying the shaking frequency and amplitude. These results will be useful for controlling the valley degree of freedom with ultracold atoms in an optical lattice.

We introduce a type of lens that focuses a plane wave into a spherical one, where light comes from all directions. Our method also suggests the design of ideal optical tweezers or, in the reverse direction, photodetection of nearly all of the light emitted from an omnidirectional source. Our design trades off simple isotropic nonmagnetic materials for requiring a high refractive index. Despite many challenges, we believe that our proposed lens can evolve, with optimization and some help from conventional lenses, to fabricable lenses that will help in boosting collection efficiency of photons in ion-photon quantum experiments.

We extend the theory of the radiation pressure to include quadratic fluctuations in the position of a moving mirror. This enables the introduction of a generalized radiation pressure operator that captures higher-order effects in the mirror-field coupling. For mechanical resonators with frequencies comparable to the fundamental cavity frequency, the resulting corrections to the optomechanical Hamiltonian are quadratic in the standard radiation pressure coupling. These corrections are expected to play a significant role in the strong-coupling regime of optomechanics, electromechanics, and superconducting circuit analogs.

We study how to include the inner horizon in the analog of rotating black holes using photon fluids. We find that a vortex beam carrying an improved phase can simulate the rotating Bañado-Teitelboim-Zanelli (BTZ) black holes experimentally. In the experiment, we develop a new photon fluid model in a graphene-methanol thermal optical solution, and measure the variation of photon fluid velocity with the radial position using a Fourier plane light-spot localization method, while also determining the variation of phonon velocity with the same radial position from the optical vortex intensity distribution. The result provides an extension for the application of optical vortex and a potential possibility for the future experimental exploration about the properties of BTZ black holes and even the anti–de Sitter space.

Photonic lattice modulations, such as lattice distortions achieved by stress-strain engineering, have been crucial for the development of various fields of photonics, in particular, topological photonics. Here we modulate the Hermitian and non-Hermitian photonic graphene lattices by utilizing a Lorentz-like transformation applied to the lattice sites. The modulated lattice may fall into two categories, according to the symmetry axis of the lattice. If the axis is aligned in the diagonal direction through the unit cells, the lattice belongs to case II; otherwise, it belongs to case I. For the case-I transformed lattice, the Dirac cones always disappear from the band structure, whereas for the case-II transformed lattice, the Dirac cones only disappear if the transformation angle $\theta$ is larger than that of the regular lattice, $\theta =\pi /2$. The Lorentz-like transformation always helps to restore the parity-time ($\mathcal{PT}$) symmetry in the non-Hermitian case-I photonic graphene lattices. In the case II of transformed non-Hermitian lattices, the $\mathcal{PT}$ symmetry can be restored as well, but only for $\theta >\pi /2$. When $\theta <\pi /2$, one obtains exceptional lines in the band structure of the lattice. These results demonstrate that the Lorentz-like transformation can serve as an effective tool to modulate photonic lattices and thus may inspire novel ideas in the manipulation of photonic topological insulators.

In this paper, we propose a single-photon routing scheme using a hybrid system, where a two-level giant atom is coupled to a pair of one-dimensional coupled-resonator waveguides. Using the discrete-coordinate scattering approach, exact expressions of the four scattering coefficients are obtained, and the single-photon routing properties are studied. We find that the single-photon routing properties are closely related to the size of the giant atom, the coupling strength between the giant atom and waveguides, and the phase difference between two coupled channels of the atom-upper (lower) waveguide. Without considering the effect of phases of the atom-waveguide coupling coefficients, the probability for a single-photon routing from one waveguide to the other does not exceed $50\%$. However, by properly selecting coupling points between the giant atom and two waveguides, and the phase difference between two atom-upper (lower) waveguide coupling coefficients, a single photon can be transferred from the input port to an arbitrarily selected output port deterministically, i.e., with $100\%$ probability. It is also found that chiral and nonreciprocal single-photon scattering can be realized in our model by properly adjusting the phase difference between two atom-upper (lower) waveguide coupled channels. Our paper offers a promising route towards achieving tunable single-photon routing and constructing optical scalable quantum networks.

We propose a scheme to generate and manipulate nonreciprocal photon blockade effect in an asymmetrical Fabry-Pérot cavity, which consists of a single two-level atom and a second-order nonlinear medium. By utilizing the intrinsic spatial asymmetry of cavity and applying a parametric amplification pumping laser to the nonlinear medium, we can realize direction-dependent single-photon and two-photon blockade effects. For nonreciprocal single-photon blockade, our proposal is robust across a wide range of parameters, such as the cavity or atomic detuning, coupling strength, and atomic decay. Within similar parameter ranges, nonreciprocal two-photon blockade can be achieved and modulated by finely adjusting the parametric amplification pumping. Our project offers a feasible access to generating high-quality and tunable nonreciprocal single- or two-photon sources and paves a new avenue for investigating the nonreciprocity of photon quantum statistical properties.

A quantum measurement generates genuine quantum randomness if and only if it breaks coherence and disturbs the measured state (and a following incompatible measurement). Here, we establish a quantitative relation between the generated randomness and its disturbance effect and provide a source-independent randomness verification protocol. Our protocol employs a few assumptions: (I) independence between the source and the measurement devices and (II) the Lüders' rule for measurement devices. Without involving heavy mathematical machinery, the generated quantum randomness can be directly estimated with the disturbance effect. In addition to the previously mentioned basic assumptions about measurements, we can improve our estimation by integrating additional measurement information for further optimization. Our protocol shows a high efficiency and yields a higher randomness generation rate than the existing one based on the uncertainty relation [G. Vallone et al., Phys. Rev. A 90, 052327 (2014)].

We provide an expression for the decoherence rate in spatial superpositions due to scattering or collision with air molecules which is independent of the wavelength of the air molecules. This result reproduces the short- and long-wavelength limits known in the literature. We compare the decoherence rate with several existing interpolations in the literature and evaluate the decoherence rate and experimental parameters when creating macroscopic quantum spatial superpositions (i.e., in micron-size spheres). The interpolation regime is relevant in, e.g., matter-wave interferometry, where one might switch between the wavelength limits during the experimental protocol. Finally, we consider the decoherence rate's time dependence while creating and closing the spatial superposition in an interferometer setup.

Calculations of the two-loop electron self-energy for the $n=1$ and $n=2$ states of hydrogen-like ions are reported, performed to all orders in the nuclear binding strength parameter $Z\alpha$ (where $Z$ is the nuclear charge number and $\alpha$ is the fine structure constant). The presented approach features an accelerated convergence of the partial-wave expansion and allows calculations to be accomplished for nuclear charges lower than previously possible and with a higher numerical accuracy.

This work is a companion paper to X.-Y. Gao et al., Phys. Rev. Lett. 134, 153402 (2025), where we discuss the nonequilibrium two-body loss dynamics of a single-component ultracold Fermi gas and its possible thermalization. This paper provides detailed information on the derivation and analysis of the inelastic quantum Boltzmann equation (IQBE) used to describe the system. We demonstrate that the Mellin transform is a powerful tool for solving and approximating the IQBE for free-space systems. In this case, the particle-number dynamics are beyond the description of the widely used phenomenological two-body equation. For harmonically trapped systems, we propose a fast-flowing approximation to simplify the numerical evaluation of the IQBE. We verify the approximation in an analogous quasi-one-dimensional system and apply it to three-dimensional calculations, obtaining satisfactory agreement with recent experimental results. Furthermore, we compare the nonequilibrium results with those obtained using a thermal ansatz in both situations, providing a systematic understanding of the antievaporation phenomena observed in such systems.

We investigate the influence of the distribution of atom velocities in a hot rubidium sample on the correlation between field-intensity fluctuations of two independently generated four-wave mixing signals and between the transmission signals. The nonlinear process is driven by a single continuous-wave (cw) laser in a pure two-level system due to the forward geometry with circular and parallel polarization of the input fields. The intensity cross correlations of the four-wave mixing signals and the transmission signals present an oscillatory behavior with a clear dependence on the power of the incident fields, which indicates a connection with Rabi oscillations. A two-level theoretical model using stochastic differential equations to account for the mechanism of conversion of phase noise into amplitude noise shows good agreement with our experimental results. Moreover, we show how the response of the system is affected by the different atomic velocity groups.

We present and theoretically demonstrate a method for generating helicity-selected near-circularly polarized attosecond pulses in mixed He-Ne gases using bichromatic counter-rotating circularly polarized (BCCP) fields. High-order harmonics driven by BCCP fields exhibit circular polarization for individual orders in the frequency domain, but adjacent orders have opposite helicities. By utilizing the He-Ne mixture, we select only one helical component of the harmonics, resulting in the generation of highly elliptically polarized attosecond pulses in the time domain. Our analyses based on the quantum-orbit theory and the strong-field approximation further clarify that the polarization of attosecond pulses is governed by the interference mechanism of high-order harmonics emitted by He and Ne. This combination of BCCP fields and an atomic mixture which requires no alignment in experiments significantly simplifies the generation of elliptically polarized harmonics dominated by one helical component, thereby paving the way for an efficient and robust method to generate bright attosecond pulses with large ellipticity.

We present a method to shape a neutron beam and project any specified target image using a single universal patterned mask that is transversely displaced. The method relies on “ghost projection,” which is a reversed form of classical ghost imaging. A set of submask regions that combine to construct the required beam shape is computed; illumination of each region with the determined exposure time projects the shaped beam. We demonstrate this method experimentally, using the Dingo neutron imaging beamline at the OPAL nuclear research reactor (Australia). The ability to shape a neutron beam “on demand” allows selective dose delivery away from sensitive areas of samples, such as in cultural heritage artifacts. It also benefits irradiation techniques, e.g., in testing the resilience of electronic components for space and defense technologies or neutron therapies.

Exceptional points (EPs) are singularities in non-Hermitian systems where the transmission spectrum exhibits significant variation at the phase transition point. Here, we propose a practical method for investigating the optomechanically induced transparency spectrum in a non-Hermitian cavity optomechanical system. By exploiting two kinds of exceptional surfaces (ESs) derived from the design of the waveguide structure, we study the transmission spectra and fast-slow light phenomena at various EPs on these ESs, and we identify ES-protected transmission spectra that are robust to parameter fluctuations. Consequently, the system exhibits a complete reversal of both transmission and fast-slow light behavior at EPs compared with those at non-EPs when the phase transition occurs. Unlike previous studies that focus solely on an isolated EP, our approach enables the exploration of system characteristics with different EPs, providing greater flexibility for experimental design.