We put forward complementary relations of entanglement, coherence, steering inequality violation, and Bell nonlocality for arbitrary three-qubit states. We show that two families of genuinely entangled three-qubit pure states with a single parameter exist, and they exhibit maximum coherence and steering inequality violation for a fixed amount of negativity, respectively. It is found that the negativity is exactly equal to the geometric mean of bipartite concurrences for the three-qubit pure states, although the negativity is always less than or equal to the latter for three-qubit mixed states. Moreover, the complementary relation between negativity and first-order coherence for tripartite entanglement states is established. Furthermore, we investigate the close relation between the negativity and the maximum steering inequality violation. In addition, the complementary relation between negativity and the maximum Bell-inequality violation for arbitrary three-qubit states is obtained. The results provide reliable evidence of fundamental connections among entanglement, coherence, steering inequality violation, and Bell nonlocality.

The nuclear polarizability effects in the hyperfine splitting of light atomic systems are not well known. The only system for which they were previously calculated is the hydrogen atom, where these effects were shown to contribute about 5% of the total nuclear correction. One generally expects the polarizability effects to become more pronounced for composite nuclei. In the present paper we determine the nuclear polarizability correction to the hyperfine splitting in ${\mathrm{He}}^{+}$ by comparing the effective Zemach radius deduced from experimental hyperfine splitting with the Zemach radius obtained from electron scattering. We obtain a surprising result that the nuclear polarizability of the helion yields just 3% of the total nuclear correction, which is smaller than for the proton.

We study the role of dark and bright autoionizing states (AISs) in photoionization and high-order harmonic generation (HHG) using a one-dimensional helium model. This model allows numerical integration of the time-dependent Schrödinger equation beyond the single-electron approximation, completely taking into account electronic correlation. We find the level structure of the system and the spatial distribution of the electronic density for several states, including AIS. Studying the HHG efficiency as a function of the detuning from the resonances with AISs, we find the HHG enhancement lines. The shapes of these lines are different from the corresponding Fano lines in photoelectronic spectra, in agreement with experimental studies on HHG in helium. Moreover, we simulate HHG under the conditions when the fundamental frequency is close to the even-order multiphoton resonance with the dark AIS. We find enhanced generation of the neighboring odd harmonics. The details of the enhancement lines for these harmonics can be understood by taking into account the temporal delay between the nonresonant and resonant XUV emissions; this delay is defined by the AIS lifetime. Finally, our simulations show that resonances with dark and bright AISs enhance HHG to a similar extent.

We propose a general quantum circuit based on the swap test for measuring the quantity $\langle {\psi }_1\left|A\right|{\psi }_2\rangle$ of an arbitrary operator $A$ with respect to two quantum states $|{\psi }_{1,2}\rangle$. This quantity is frequently encountered in many fields of physics, and we dub it the generalized expectation as a two-state generalization of the conventional expectation. We apply the circuit, in the field of non-Hermitian physics, to the measurement of generalized expectations with respect to left and right eigenstates of a given non-Hermitian Hamiltonian. To efficiently prepare the left and right eigenstates as the input to the general circuit, we also develop a quantum circuit via effectively rotating the Hamiltonian pair $(H,-H^{†})$ in the complex plane. As applications, we demonstrate the validity of these circuits in the prototypical Su-Schrieffer-Heeger model with nonreciprocal hopping by measuring the Bloch and non-Bloch spin textures and the corresponding winding numbers under periodic and open boundary conditions (PBCs and OBCs), respectively. The numerical simulation shows that non-Hermitian spin textures building up these winding numbers can be well captured with high fidelity, and the distinct topological phase transitions between PBCs and OBCs are clearly characterized. We may expect that other non-Hermitian topological invariants composed of non-Hermitian spin textures, such as non-Hermitian Chern numbers, and even significant generalized expectations in other branches of physics would also be measured by our general circuit, providing a different perspective to study novel properties in non-Hermitian as well as other physics realized in qubit systems.

We study the transport of many partially distinguishable and possibly interacting particles under the action of repeated projective measurements on a target space and investigate how the particles' interference affects the mean first-detection time. We contrast the detection of exactly $n$ versus at least $n$ particles, explain divergences in the mean first-detection time through spectral properties of the generating evolution operator, and illustrate our findings by an example.

We analyze a scheme that uses quantum nondemolition measurements to induce squeezing of a two-mode Bose-Einstein condensate in a double-well trap. In a previous paper [E. O. Ilo-Okeke, S. Sunami, C. J. Foot, and T. Byrnes, Phys. Rev. A 104, 053324 (2021)], we introduced a model to solve exactly the wave function for all atom-light interaction times. Here, we perform approximations for the short interaction time regime, which is relevant for producing squeezing. Our approach uses a Holstein-Primakoff approximation for the atoms while we treat the light variables exactly. It allows us to show that the measurement induces correlations within the condensate, which manifest in the state of the condensate as a superposition of even-parity states. In the long interaction time regime, our methods allow us to identify the mechanism for loss of squeezing correlation. We derive simple expressions for the variances of atomic spin variables conditioned on the measurement outcome. We find that the results agree with the exact solution in the short interaction time regime. Additionally, we show that the expressions are the sum of the variances of the atoms and the measurement. Beyond the short interaction time regime, our scheme agrees qualitatively with the exact solution for the spin variable that couples to light.

Tunneling ionization is characterized by a negative time delay, observed asymptotically as a specific shift of the photoelectron momentum distribution, which is caused by the interference of the sub-barrier recolliding and direct ionization paths. In contrast, a Gedankenexperiment following the peak of the wave function shows a positive tunneling time delay at the tunnel exit, considering only the direct ionization path. In this paper we investigate the effects of sub-barrier recollisions on the time delay pattern at the tunnel exit. We conclude that the interference of the direct and recolliding trajectories decreases the tunneling time delay at the exit by the value equal to the asymptotic time delay, maintaining, however, its sizable positive value. Finally, we discuss the recent experiment [Yu et al., Light Sci. Appl. 11, 215 (2022)] addressing the tunneling time in a modified two-color attoclock setup. The analysis of the experimental findings with our theoretical model indicates the physical necessity to introduce an additional time characteristic for tunneling ionization—the time delay describing the initiation of the tunneling wave packet.

Single-component ultracold atomic Fermi gases are usually described using noninteracting many-fermion models. However, recent experiments reached a regime where $p$-wave interactions among identical fermionic atoms are important. In this paper, we employ variational and fixed-node diffusion Monte Carlo simulations to investigate the ground-state properties of single-component Fermi gases with short-range repulsive interactions. We determine the zero-temperature equation of state, and elucidate the roles played by the $p$-wave scattering volume and the $p$-wave effective range. A comparison against recently derived second-order perturbative results shows good agreement in a broad range of interaction strength. We also compute the quasiparticle effective mass, and we confirm the perturbative prediction of a linear contribution in the $p$-wave scattering volume, while we find significant deviations from the beyond-mean-field perturbative result, already for moderate interaction strengths. Finally, we determine ground-state energies for two-component unpolarized Fermi gases with both interspecies and intraspecies hard-sphere interactions, finding remarkable agreement with a recently derived fourth-order expansion that includes $p$-wave contributions.

We discuss the anomalous behavior of the Faraday (transmission) and polar Kerr (reflection) rotation angles of the propagating light, in finite periodic $\mathcal{P}\mathcal{T}$-symmetric structures, consisting of $N$ cells. The unit-cell potential is two complex $\delta$ potentials placed on both boundaries of the ordinary dielectric slab. It is shown that, for a given set of parameters describing the system, a phase transitionlike anomalous behavior of Faraday rotation (FR) and Kerr rotation (KR) angles in a parity-time-symmetric system can take place. In the anomalous phase the value of one of the Faraday and Kerr rotation angles can become negative, and both angles suffer from spectral singularities and give a strong enhancement near the singularities. We also show that the real part of the complex angle of KR, ${\theta }_1^R$, is always equal to the ${\theta }_1^T$ of FR, no matter what phase the system is in due to the symmetry constraints. The imaginary part of KR angles ${\theta }_2^{R^{r/l}}$ is related to the ${\theta }_2^T$ of FR by parity-time symmetry. Calculations based on the approach of the generalized nonperturbative characteristic determinant, which is valid for a layered system with randomly distributed delta potentials, show that the Faraday and Kerr rotation spectrum in such structures has several resonant peaks. Some of them coincide with transmission peaks, providing simultaneous large Faraday and Kerr rotations enhanced by one or two orders of magnitude. We provide a recipe for funding a one-to-one relation in between KR and FR.

We show that optomechanical quantum systems can undergo dissipative phase transitions within the limit of a small nonlinear interaction and strong external drive. In such a defined thermodynamical limit, the nonlinear interaction stabilizes optomechanical dynamics in strong- and ultrastrong-coupling regimes. As a consequence, optomechanical systems possess a rich phase diagram consisting of periodic orbits and discontinuous and continuous dissipative phase transitions with and without bifurcation. We also find a critical point where continuous and discontinuous dissipative phase transition lines meet. Our analysis demonstrates that optomechanical systems are valuable for understanding the rich physics of dissipative phase transitions and ultrastrong-coupling regimes.

In this paper we show how to generate multiple single-photon wave packets of arbitrary temporal shape from an optical cavity coupled with $N$ three-level atoms driven by a driving field in the non-Markovian regime. We derive an exact analytical expression of the optimal driving field to generate such wave packets, which depends on two detunings of the cavity and driving field with respect to the three-level atoms. The cavity we use consists of two mirrors facing each other, where one is perfect and the other includes dissipation (a one-sided cavity), which couples with the corresponding non-Markovian input-output fields. If the first single-photon wave packet generated by the Markovian system is the same as the non-Markovian case, the Markovian system cannot generate the same multiple single-photon wave packets as the non-Markovian system when the spectral widths of the other environments take values different from the spectral width of the first environment, while setting the equal spectral widths for the different environments can generate this. The generated multiple different single-photon wave packets are not independent of each other, which satisfies certain relations with non-Markovian spectral parameters. We analyze the transition from Markovian to non-Markovian regimes and compare the differences between them, where the cavity interacts simultaneously with the multiple non-Markovian environments. Finally, we extend the above results to a general non-Markovian quantum network involving many cavities coupled with driven three-level atoms.

Quantum mechanically, a driving process is expected to be reversible in the quasistatic limit, also known as the adiabatic theorem. This statement stands in opposition to classical mechanics, where a mix of regular and chaotic dynamics implies irreversibility. A paradigm for demonstrating the signatures of chaos in quantum irreversibility is a sweep process whose objective is to transfer condensed bosons from a source orbital. We show that such a protocol is dominated by an interplay of adiabatic-shuttling and chaos-assisted depletion processes. The latter is implied by interaction terms that spoil the Bogoliubov integrability of the Hamiltonian. As the sweep rate is lowered, a crossover to a regime that is dominated by quantum fluctuations is encountered, featuring a breakdown of quantum-to-classical correspondence. The major aspects of this picture are not captured by the common two-orbital approximation, which implies failure of the familiar many-body Landau-Zener paradigm.

The analysis of a continuous measurement record $z\left(t\right)$ poses a fundamental challenge in quantum measurement theory. Different approaches were used in the past as records can, e.g., exhibit predominantly Gaussian noise, telegraph noise, or clicks at random times. The last case may appear as photon clicks in an optical spin-noise measurement at very low probe laser power. Here we show that such random-time quantum measurements can, similarly to the first two cases, be analyzed in terms of higher-order temporal correlations of the detector output $z\left(t\right)$ and be related to the Liouvillian of the measured quantum system. Our analysis in terms of up to fourth-order spectra (quantum polyspectra) shows that this type of spectra reveals the same valuable information as previously studied higher-order spectra in the case of the usual continuous quantum measurements. Surprisingly, broadband system dynamics is revealed even for deliberately low average measurement rates. Many applications are envisioned in high-resolution spectroscopy, single-photon microscopy, circuit quantum electrodynamics, quantum sensing, and quantum measurements, in general.

The Liouville theorem states that the phase-space volume of an ensemble in a closed system remains constant. While gases of material particles can efficiently be cooled by sympathetic or laser cooling techniques, allowing for large phase-space compression upon suitable coupling to the environment, for light both the absence of an internal structure, as well as the nonconservation of photons upon contact with matter imposes fundamental limits for three-dimensional light-harvesting systems, such as fluorescence-based light concentrators. An advantageous physical situation can in principle be expected for dye-solution-filled microcavities with a mirror spacing in the wavelength range, where low-dimensional photon gases with nonvanishing and tunable chemical potential have been experimentally realized. Motivated by the goal to observe phase-space compression of sunlight by cooling the captured radiation to room temperature, in this work we theoretically show that in a lossless, harmonically confined system the phase-space volume scales as ${\left(\mathrm{\Delta }x\mathrm{\Delta }p/T\right)}^d=\mathrm{constant}$, where $\mathrm{\Delta }x$ and $\mathrm{\Delta }p$ denote the position and momentum spread and $d$ the dimensionality of the system ($d=1$ or 2). Experimentally, we realize a corresponding sunlight-pumped dye microcavity and demonstrate thermalization of scattered sunlight to a two-dimensional room temperature photon gas with nonvanishing chemical potential. Prospects of phase-space buildup of light by cooling, as can be feasible in systems with a two- or three-dimensional band gap, range from quantum state preparation in tailored potentials up to technical applications for more efficient collection of diffuse sunlight.

We demonstrate a simple and robust high-resolution ghost spectroscopy approach for x-ray and extreme ultraviolet transient absorption spectroscopy at free-electron laser sources. To retrieve the sample response, our approach requires only an online spectrometer before the sample and a downstream bucket detector. We validate the method by measuring the absorption spectrum of silicon, silicon carbide, and silicon nitride membranes in the vicinity of the silicon $L_{2,3}$ edge and by comparing the results with standard techniques for absorption measurements. Moreover, we show that ghost spectroscopy allows the high-resolution reconstruction of the sample spectral response to optical pumps using a coarse energy scan with self-amplified spontaneous emission radiation.

Modeling the behavior of superconducting electronic circuits containing Josephson junctions is crucial for the design of superconducting information processors and devices. In this paper, we introduce DEC-QED, a computational approach for modeling the electrodynamics of superconducting electronic circuits containing Josephson junctions in arbitrary three-dimensional electromagnetic environments. DEC-QED captures the nonlinear response and induced currents in BCS superconductors and accurately captures phenomena such as the Meissner effect, flux quantization, and Josephson effects. Using a spatial coarse-graining formulation based on discrete exterior calculus (DEC), DEC-QED can accurately simulate transient and long-time dynamics in superconductors. The expression of the entire electrodynamic problem in terms of the gauge-invariant flux field and charges makes the resulting classical field theory suitable for second quantization.

We study the quantum-mechanical motion of massive particles in a system of two coupled waveguide potentials, where the population transfer between the waveguides effectively acts as a clock and allows particle velocities to be determined. Application of this scheme to evanescent phenomena at a reflective step potential reveals an energy-velocity relationship for classically forbidden motion. Regions of gain and loss, as described by imaginary potentials, are shown to speed up the motion of particles. We argue that phase and density gradients in quantum-mechanical wave functions play complementary roles in indicating the speed of particles.

Quantum random-number generation (QRNG) is one of the most widely applied branches in quantum cryptography. Among all QRNG schemes, semi-device-independent (semi-DI) QRNG is quite promising, achieving high randomness generation rates with few assumptions on the devices. For the central task of a QRNG study—security analysis—numerical approaches become popular for its generality to various semi-DI QRNG schemes. Here we formulate a numerical framework for the finite-size security of general semi-DI QRNGs, which gives a secure lower bound of the finite-size randomness generation rate against general attacks. We consider a simple example of an optical semi-DI QRNG as an application of our framework.