A theoretical scheme based on the nonadiabatic geometric quantum computation (NGQC) is proposed to realize quantum cloning in the Rydberg atom system. In contrast to previous schemes, the present one utilizes the NGQC to construct the clone machine and thus is more robust against control errors. Meanwhile, to implement the desired cloning framework in the quantum clone machine, the scheme reported by Zhu and Ye [M.-Z. Zhu and L. Ye, Phys. Rev. A 91, 042319 (2015)] based on cavity QED requires a series of single(two)-qubit operations. For the present NGQC-based scheme, through modulating the rotation angle of geometric operations, we can greatly simplify the process of realizing the cloning framework. In addition, through adjusting the relevant parameters, the scheme can perform symmetrical (asymmetrical) universal cloning, optimal symmetrical (asymmetrical) phase-covariant quantum cloning, and optimal symmetrical (asymmetrical) real-state quantum cloning. The present attempt to optimize quantum cloning using geometric quantum control in Rydberg atoms provides a path to robust and simplified quantum cloning, which is meaningful for experiments and has implications for quantum cloning in other quantum systems as well.

Time-frequency entangled photons constitute an important resource for a plethora of applications across the diverse quantum technology landscape. Thus, efficient and tunable setups for the generation of entangled photons are requisite for modern quantum technologies. In this work, we propose a generic cavity QED setup designed for on-demand generation of time-frequency entangled photon pairs, with each photon propagating in a separate waveguide. We outline a potential incarnation of this setup in the microwave superconducting circuit QED architecture. We derive and numerically solve the set of equations of motion governing the evolution of the quantum state of the system, allowing us to examine the photon emission dynamics. Using the Schmidt decomposition of the joint spectral amplitude of the emitted photon pair, we compute the entanglement entropy analyzing its dependence on the system parameters. We outline the potential extension of the proposed scheme for the generation of multiphoton time-frequency entangled states.

We explore the dynamical transport of an impurity between different embedding majority species, which are spatially separated in a double well. The transfer and storage of the impurity is triggered by dynamically changing the interaction strengths between the impurity and the two majority species. We find a simple but efficient protocol consisting of linear ramps of majority-impurity interactions at designated times to pin or unpin the impurity. Our study of this highly imbalanced few-body triple mixture is conducted with the multilayer multiconfiguration time-dependent Hartree method for atomic mixtures, which accounts for all interaction-induced correlations. We analyze the dynamics in terms of single-particle densities and entanglement growth and provide an effective potential description involving mean fields of the interacting components. The majority components remain self-trapped in their individual wells at all times, which is a crucial element for the effectiveness of our protocol. During storage times each component performs low-amplitude dipole oscillations in a single well. Unexpectedly, the interspecies correlations possess a stabilizing impact on the transport and storage properties of the impurity particle.

Fully excited two-level atoms separated by less than the transition wavelength cooperatively emit light in a short burst, a phenomenon called superradiance by R. Dicke in 1954 [Phys. Rev. 93, 99 (1954)]. The burst is characterized by a maximum intensity scaling with the square of the number of atoms $N$ and a temporal width reduced by $N$ compared to the single atom spontaneous decay time. Both effects are usually attributed to a synchronization of the electric dipole moments of the atoms occurring during the process of light emission. Contrary to this explanation, it was recently shown by use of a quantum path description that the peak intensity results from the quantum correlations among the atoms when occupying symmetric Dicke states. Here we investigate from this perspective the temporal evolution of the ensemble, starting in the small sample limit, i.e., when the atoms have mutual separations much smaller than the transition wavelength $\lambda$ and pass down the ladder of symmetric Dicke states. In addition, we explore the temporal evolution for the case of distant noninteracting atoms with mutual separations much larger than $\lambda$. We show that in this case a similar superradiant burst of the emitted radiation is observed if the quantum correlations of the atoms are generated by conditional photon measurements retaining the atomic ensemble within or close to the symmetric subspace.

We investigate the dynamics of a noninteracting spin system, undergoing coherent Rabi oscillations, in the presence of stochastic resetting. We show that resetting generally induces long-range quantum and classical correlations both in the emergent dissipative dynamics and in the nonequilibrium stationary state. Moreover, for the case of conditional reset protocols—where the system is reinitialized to a state dependent on the outcome of a preceding measurement—we show that in the thermodynamic limit, the spin system can feature collective behavior which results in a phenomenology reminiscent of that occurring in nonequilibrium phase transitions. The discussed reset protocols can be implemented on quantum simulators and quantum devices that permit fast measurement and readout of macroscopic observables, such as the magnetization. Our approach does not require the control of coherent interactions and may therefore highlight a route towards a simple and robust creation of quantum correlations and collective nonequilibrium states, with potential applications in quantum enhanced metrology and sensing.

We investigate the set of quantum states that can be shown to be $k$-incoherent based only on their eigenvalues (equivalently, we explore which Hermitian matrices can be shown to have small factor widths based only on their eigenvalues). In analogy with the absolute separability problem in quantum resource theory, we call these states “absolutely $k$-incoherent,” and we derive several necessary and sufficient conditions for membership in this set. We obtain many of our results by making use of recent results concerning hyperbolicity cones associated with elementary symmetric polynomials.

In the light of a multiple scattering (MS) description of molecular photodiffraction and photoabsorption processes, we present an investigation of the interplay between initial state coherence and intramolecular scattering, leading to a reinterpretation of the molecular interference in diatomic molecules and in particular of the Cohen-Fano (CF) interference term in photoabsorption. Indeed, the delocalization of the initial state electron over different atoms at positions ${\mathbf{R}}_n$ introduces in the language of MS theory as many virtual emitters as there are atoms in the molecule, giving rise to new MS paths as compared to the case of a single emitter. Their emission amplitudes interfere via the usual phase factor $e^{i\mathbf{k}·{\mathbf{R}}_n}$ and in the case of two emitter photoemission describe how the usual picture of the microscopic Young's experiment is modified by the presence of intramolecular scattering. Photoabsorption follows from photoemission by integrating over the emission directions of the photoelectron and characterizes the CF oscillations as the remnants on the energy scale of the photoemission interference patterns introduced by the new paths joining the two centers, exactly like the extended x-ray absorption fine structure signals are the remnants of the closed paths that begin and end at the same atom. In the same context of initial state coherence we also show that the orientationally averaged scattering of electrons off small molecules can give access to CF type of oscillations, although in a more complicated way, due to the lack of site selectivity in comparison with the photoemission process and the absence of a dipole selection rule. It is shown that this type of modulation has the same physical origin as that found in photoabsorption.

We discuss the quantum Hall response of SU(3) fermions in two-dimensional lattices, when artificial magnetic flux and color-orbit coupling are present. We analyze the Hall conductance tensor in the charge-charge, color-charge, charge-color, and color-color sectors. When charge and color are conserved, we directly relate the Hall conductances to corresponding Chern numbers describing topological color insulators. We establish the bulk-edge correspondence for Hall conductances in toroidal (without edges) and cylindrical (with edges) geometries. When color is not conserved or when edge states are not robust to disorder or SU(3)-symmetric interactions, we show that the color Hall conductances are not quantized, but the corresponding Chern numbers, which are a bulk property, can still be used to label the topological insulating phases. Depending on the robustness of edge states to disorder and interactions, we identify the topological phases to be strong, intermediate, or weak. We envision applications to $\mathrm{SU}\left(N\right)$ ultracold fermions such as ${}^{173}\mathrm{Yb}$ and ${}^{87}\mathrm{Sr}$.

Airy beams are known for displaying shape invariance and self-acceleration along the transverse direction while they propagate forwards. Although these properties could be associated with the beam coherence, it has been revealed that they also manifest in the case of partially coherent Airy-type beams. Here, these properties are further investigated by introducing and analyzing a class of partially coherent Airy beams under both infinite and finite energy conditions. The key element within the present approach is the so-called cross-spectral density, which enables a direct connection with the quantum density matrix, making the analysis exportable to the quantum realm to study the dynamics of Airy wave packets acted by both incoherence and decoherence. As it is shown, in the case of infinite energy beams both properties are preserved even under the circumstance of total incoherence provided the underlying structure of the beam remains equal to that of an Airy beam. In the case of finite energy beams, a situation closer to a realistic scenario as experimental beams cannot have an infinite extension, it is shown that a propagation range along which both properties are preserved can be warranted. This is controlled by a critical distance, which depends on the spread range determined by the parameters ruling the extension of random field spatial fluctuations. Such a distance is determined by defining a position-dependent parameter that quantifies the degree of overlapping between the propagated beam and the input one displaced by an amount equivalent to the propagation distance.

In this paper, we consider the orthogonal product set (OPS) with strong quantum nonlocality in multipartite quantum systems. Based on the decomposition of plane geometry, we present a sufficient condition for the triviality of orthogonality-preserving positive operator-valued measures on fixed subsystem and partially answer an open question given by Yuan et al. [Phys. Rev. A 102, 042228 (2020)]. The connection between the nonlocality and the plane structure of OPSs is established. We successfully construct a strongly nonlocal OPS in ${\mathcal{C}}^{d_A}\otimes {\mathcal{C}}^{d_B}\otimes {\mathcal{C}}^{d_C}(d_A,d_B,d_C\ge 4)$, which contains fewer quantum states, and generalize the structures of known OPSs to any possible three and four-partite systems. In addition, we propose several entanglement-assisted protocols for perfectly local discrimination of the sets. It is shown that the protocols without teleportation use less entanglement resources that on average and these sets can always be discriminated locally with multiple copies of two-qubit maximally entangled states. These results also exhibit nontrivial signification of maximally entangled states in the local discrimination of quantum states.

We investigate robustness of probabilistic storage and retrieval device optimized for phase gates to noise. We use noisy input composed of convex combination of unitary channel with either depolarizing or dephasing channel. We find out that the resistance to dephasing noise is higher than to depolarization. Interestingly, for the depolarization the retrieval reduces the degree of noise. We also examine the possible realizations showing that their performance is different when the noise is present.

In a recent experiment, a dissipative Aharonov-Bohm (AB) chain was implemented in the momentum space of a Bose-Einstein condensate. Formed by a series of dissipative AB rings threaded by synthetic magnetic flux, the chain exhibits the non-Hermitian skin effect, necessitating the non-Bloch band theory to account for its topology. In this work, we systematically characterize topological features of the dissipative AB chain, particularly beyond the experimentally realized parameter regime. Further, we show that atom-injection spectroscopy is capable of revealing not only topological edge states, as has been demonstrated in the experiment, but also the general band structure of the system. We then discuss alternative dynamic detection schemes for the topological edge states. Given the generality of the model and the detection schemes, our work is helpful for future studies of topological models with non-Hermitian skin effects across a variety of quantum simulators.

Conventionally the mobility edge (ME) separating extended states from localized ones is a central concept in understanding Anderson localization transition. The critical state, being delocalized and nonergodic, is a third type of fundamental state that is different from both the extended and localized states. Here we study the localization phenomena in a one-dimensional periodically kicked quasiperiodic optical Raman lattice by using fractal dimensions. We show a rich phase diagram including the pure extended, critical, and localized phases in the high-frequency regime, the MEs separating the critical regions from the extended (localized) regions, and the coexisting phase of extended, critical, and localized regions with increasing the kicked period. We also find the fragility of phase boundaries, which are more susceptible to the dynamical kick, and the phenomenon of the reentrant localization transition. Finally, we demonstrate how the studied model can be realized based on current cold atom experiments and how to detect rich physics by expansion dynamics. Our results provide insight into studying and detecting critical phases, MEs, coexisting quantum phases, and some other physics phenomena in the periodically kicked systems.

There has been a very large body of research on searching a marked vertex on a graph based on quantum walks, and Grover's algorithm can be regarded as a quantum walk-based search algorithm on a special graph. However, the existing quantum walk-based search algorithms suffer severely from the soufflé problem, which mainly means that the success probability of finding a marked vertex could shrink dramatically, even to zero, when the number of search steps is greater than the right one, thus heavily reducing the robustness and practicability of the algorithm. Surprisingly, while the soufflé problem of Grover's algorithm has attracted enough attention, how to address this problem for general quantum walk-based search algorithms is missing in the literature. Here we initiate the study of overcoming the soufflé problem for quantum walk-based search algorithms by presenting a quantum walk-based search framework that achieves robustness without sacrificing the quantum speedup. In this framework, for any adjustable parameter $\epsilon$, the quantum algorithm can find a marked vertex on an $N$-vertex complete bipartite graph with probability at least $1-\epsilon$, whenever the number of search steps $h$ satisfies $h\ge ln\left(\frac{2}{\sqrt{\epsilon }}\right)\sqrt{N}+1$. Note that the algorithm need not know the exact number of marked vertices. Consequently, we obtain quantum search algorithms with stronger robustness and practicability.

Understanding collective phenomena calls for tractable descriptions of correlations in assemblies of strongly interacting constituents. Capturing the essence of their self-consistency is central. The parquet theory admits a maximum level of self-consistency for strictly pairwise many-body correlations. While perturbatively based, the core of parquet and allied models is a set of strongly coupled nonlinear integral equations for all-order scattering; tightly constrained by crossing symmetry, they are nevertheless heuristic. Within a formalism due to Kraichnan, we present a Hamiltonian analysis of fermionic parquet's structure. The shape of its constitutive equations follows naturally from the resulting canonical description. We discuss the affinity between the derived conserving scattering amplitude and that of standard parquet. Whereas the Hamiltonian-derived model amplitude is microscopically conserving, it cannot preserve manifest crossing symmetry. The parquet amplitude and its refinements preserve crossing symmetry, yet cannot safeguard conservation at any stage. Which amplitude should be used depends on physics rather than on theoretically ideal completeness.

In an entanglement swapping scenario, if two sources distributing entangled states between three parties are independent, local correlations lead to a different kind of inequality than the standard Bell inequalities, known as network local models. A highly demanding task is to find out a way to involve many players nontrivially in a quantum network since measurements, in general, disturb the system. To this end, we consider here an alternative way of sharing network nonlocality when two observers initially share a maximally entangled, a nonmaximally entangled and a noisy entangled state. We report that by employing unsharp measurements performed by one of the observers, at most six pairs can sequentially demonstrate the violation of bilocal inequality while a maximum of two pairs of observers can exhibit bi-nonlocality when both the observers perform unsharp measurements. We also find the critical noise involved in unsharp measurements in each round to illustrate the bi-nonlocality for a fixed shared entangled state as a resource. We also connect the entanglement content of the shared state, quantified via von-Neumann entropy for pure states and entanglement of formation for Werner states with the maximum number of rounds showing violation of bilocal inequality. By considering elegant joint measurement at the node such that the entanglement content in the elements of the joint measurement by the third party gets reduced, we observe that the maximum number reduces to two sequential sharing of bi-nonlocality even for the maximally entangled state when the settings at each side are taken to be three and fixed.

Transitionless quantum driving is a useful approach to mimic the adiabatic evolution of a quantum system so that the system can rapidly evolve from its initial state to the target state without transitions between instantaneous eigenstates of the reference Hamiltonian. To quantify the energetic cost in the transitionless quantum driving process, the instantaneous cost is defined as the Frobenius norm of the driving Hamiltonian and the integral of instantaneous cost is used to describe the total cost in the entire evolution. In this paper, we find that the minimal integral of instantaneous cost has a geometric property being equal to the length of the evolution path on the Riemannian manifold spanned by the control parameters with a positive definite metric, but independent of the evolution details such as the changing rate of the parameters. Based on this property, we further show that the optimal transitionless quantum driving with the minimum total cost corresponds to the geodesic path on the Riemannian manifold, which provides a method for optimizing transitionless quantum driving.

We explore the potential of D-Wave's quantum annealers for computing some of the basic components required for quantum simulations of standard model physics. By implementing a basic multigrid (including “zooming”) and specializing Feynman-clock algorithms, D-Wave's Advantage is used to study harmonic and anharmonic oscillators relevant for lattice scalar field theories and effective field theories, the time evolution of a single plaquette of SU(3) Yang-Mills lattice gauge field theory, and the dynamics of flavor entanglement in four-neutrino systems.